Installing a loft floor
 

Sorry chaps, a bit of a long post but I have tried to get all the essential information in (!) Undoubtedly
there will be something I've missed out, even so....

I have to build a floor in a loft. At first this will provide a platform for some roof timber repairs to be
carried out but ultimately it will be used for storage, not living space, so there are no formal BR
requirements but, of course, I’d like it to be robust enough that it doesn’t all wind up in the bedroom below.

At present, there is a lath and plaster ceiling, with rather wimpy-looking ceiling joists, so not the most
stable platform to work on. It’s in pretty good condition (as a ceiling, not a floor) so I’d like to keep it
that way, which means installing joists clear of the ceiling timbers. This will, of course, create a void
for a good depth of insulation.

So question 1: To work above the ceiling, I’m thinking of supporting it with boards on acro jacks,
possibly moving these according to where I’m working as I go and putting some boards on the ceiling
joists to spread the load (mostly me!). Does this sound like a sensible thing to do – ie any better
suggestions?

One side of the space is an internal wall and the other side is a chimney breast with single-brick party
walls in the recesses each side (these look pretty weak). Each end is the outside wall of the house
running up about 60cm from the ceiling to the eaves of the roof. Since the shorter span (about 4m) is
from the internal wall to the chimney breast/party wall, the joists for the new floor will run this way (ie
parallel to the outside walls).

The plan is to use ledger boards (wall plates if you prefer) and joist hangers to mount 50 x 200mm
(-ish) joists at 400mm centres. I know that socketing into the brick is favoured by some but that isn’t
going to happen for many good reasons. To avoid going near the single-brick party wall, I’ll have to
use trimmers across the (approx.) 1.8m recesses each side of the chimney breast, mounting joist
hangers on these, so this is where the greatest loads will be: With 4 or 5 joists on each trimmer, their
mountings will be carrying approaching 1/3 of the floor loading. The short ledger boards that these trimmers will mount on will, of course, run at 90 degrees to the others (ie along the returns of the
chimney breast and along the outside walls).

So question 2: What’s the panel’s view on the best way to mount the ledger boards, particularly those
that carry the greatest loads? I’m thinking of resin studs between each pair of joist positions (in the
past I would have used expanding bolts but this is Victorian brick), but would a single large stud (M16)
be better or worse than a couple of smaller ones (M12) and is there any benefit in supplementing
these, with anything further (eg a pattern of multi-montis)? For the short ledger boards, I’m thinking
four studs in a rectangle around each joist hanger.
Using more mountings spreads the load, but over-perforating the boards would weaken them (though
I suspect it would take a lot for this to be a big issue).

Lastly, to get decent access into the loft space (currently a 2x2’ hatch in a cupboard), I need to create a
new doorway. The only way I can approach this is from the inside of the loft (due to obstructions I
can’t practically re-position until the opening is formed). Normally, cutting a new opening would be
best done using strongboys to support the triangle of brisk above until the lintel is installed but I’d
hesitate to jack against the top of the ceiling and getting them through the hatch wouldn’t be easy.

So question 3: Instead of using strongboys, would a board (4x1 or so) fixed to each brick (multimonti
into the brick centre) above the lintel do an adequate job of stopping everything moving while I get a
lintel in? (A bit non-standard I know, but the best option I can think of in the circumstances!)

Cheers

Installing a loft floor
 

On 17/10/2012 11:49, GMM wrote:
Sorry chaps, a bit of a long post but I have tried to get all the essential information in (!) Undoubtedly
there will be something I've missed out, even so....

I have to build a floor in a loft. At first this will provide a platform for some roof timber repairs to be
carried out but ultimately it will be used for storage, not living space, so there are no formal BR
requirements but, of course, I’d like it to be robust enough that it doesn’t all wind up in the bedroom below.

At present, there is a lath and plaster ceiling, with rather wimpy-looking ceiling joists, so not the most
stable platform to work on. It’s in pretty good condition (as a ceiling, not a floor) so I’d like to keep it
that way, which means installing joists clear of the ceiling timbers. This will, of course, create a void
for a good depth of insulation.

So question 1: To work above the ceiling, I’m thinking of supporting it with boards on acro jacks,
possibly moving these according to where I’m working as I go and putting some boards on the ceiling
joists to spread the load (mostly me!). Does this sound like a sensible thing to do – ie any better
suggestions?

Nothing wrong with it, but you may be able to get around the problem in
other ways, if you can get a few joists in without needing to load the
existing ceiling too much. Once that is done you can get a temporary
floor to work off and do the rest.

One side of the space is an internal wall and the other side is a chimney breast with single-brick party
walls in the recesses each side (these look pretty weak). Each end is the outside wall of the house
running up about 60cm from the ceiling to the eaves of the roof.

So the existing ceiling is not at the top of the wall as such then, but
is suspended a bit below it?

Since the shorter span (about 4m) is
from the internal wall to the chimney breast/party wall, the joists for the new floor will run this way (ie
parallel to the outside walls).

The plan is to use ledger boards (wall plates if you prefer) and joist hangers to mount 50 x 200mm
(-ish) joists at 400mm centres. I know that socketing into the brick is favoured by some but that isn’t
going to happen for many good reasons.

Socketing is rarely done these days it seems... hangers are the norm.

To avoid going near the single-brick party wall, I’ll have to
use trimmers across the (approx.) 1.8m recesses each side of the chimney breast, mounting joist
hangers on these, so this is where the greatest loads will be: With 4 or 5 joists on each trimmer, their
mountings will be carrying approaching 1/3 of the floor loading. The short ledger boards that these trimmers will mount on will, of course, run at 90 degrees to the others (ie along the returns of the
chimney breast and along the outside walls).

You can get strong shoes that rawl bolt to masonry, and are go for 10kN
and more... so one of those at each end of the joist will carry a
significant floor load. I needed to do one like this on my loft at my
previous place.

The bottom left of drawing:

http://internode.co.uk/temp/beam-layout.gif

Shows beam F terminating on one of these shoes. It in effect takes one
end of the entire floor load.

So question 2: What’s the panel’s view on the best way to mount the ledger boards, particularly those
that carry the greatest loads? I’m thinking of resin studs between each pair of joist positions (in the
past I would have used expanding bolts but this is Victorian brick), but would a single large stud (M16)
be better or worse than a couple of smaller ones (M12) and is there any benefit in supplementing
these, with anything further (eg a pattern of multi-montis)? For the short ledger boards, I’m thinking
four studs in a rectangle around each joist hanger.
Using more mountings spreads the load, but over-perforating the boards would weaken them (though
I suspect it would take a lot for this to be a big issue).

I can't see much advantage going for M16 over M12 since they are both
going to be significantly stronger than the timber (especially as the
loading is across the grain).

The type of hanger used also makes a difference. With a suitably rigid
one that will not attempt to "unwind" and flip the wall plate over, most
of the load is simply pushing the wall plate hard against the top of the
masonry - there should be very little lateral load.

Another option would be the masonry hangers that are designed to be
built into a leaf of brickwork. These can be retrofitted by raking out
some mortar and then mortaring back in. They don't require any bolting
as such.

Lastly, to get decent access into the loft space (currently a 2x2’ hatch in a cupboard), I need to create a
new doorway. The only way I can approach this is from the inside of the loft (due to obstructions I
can’t practically re-position until the opening is formed). Normally, cutting a new opening would be
best done using strongboys to support the triangle of brisk above until the lintel is installed but I’d
hesitate to jack against the top of the ceiling and getting them through the hatch wouldn’t be easy.

So question 3: Instead of using strongboys, would a board (4x1 or so) fixed to each brick (multimonti
into the brick centre) above the lintel do an adequate job of stopping everything moving while I get a
lintel in? (A bit non-standard I know, but the best option I can think of in the circumstances!)

That ought to do it. Is this a single leaf or double?


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

In message , John
Rumm writes
On 17/10/2012 11:49, GMM wrote:
Sorry chaps, a bit of a long post but I have tried to get all the
essential information in (!) Undoubtedly
there will be something I've missed out, even so....

Couple of thoughts... someone in here reinforced their existing joists
rather than install new.

The other.. don't allow the new timbers anywhere near the lath and
plaster. We once had a chalet bungalow where the previous owners had
stiffened up the old loft floor to take the new bedrooms load. These
joists spanned the outside walls but were not attached to the old
ceiling ones. Inevitably the new timber moved and pinged nail head
plaster off the downstairs ceiling.

--
Tim Lamb

Installing a loft floor
 

On Wednesday, October 17, 2012 3:28:07 PM UTC+1, John Rumm wrote:
On 17/10/2012 11:49, GMM wrote:

Sorry chaps, a bit of a long post but I have tried to get all the essential information in (!) Undoubtedly

there will be something I've missed out, even so....



I have to build a floor in a loft. At first this will provide a platform for some roof timber repairs to be

carried out but ultimately it will be used for storage, not living space, so there are no formal BR

requirements but, of course, I�d like it to be robust enough that it doesn�t all wind up in the bedroom below.



At present, there is a lath and plaster ceiling, with rather wimpy-looking ceiling joists, so not the most

stable platform to work on. It�s in pretty good condition (as a ceiling, not a floor) so I�d like to keep it

that way, which means installing joists clear of the ceiling timbers. This will, of course, create a void

for a good depth of insulation.



So question 1: To work above the ceiling, I�m thinking of supporting it with boards on acro jacks,

possibly moving these according to where I�m working as I go and putting some boards on the ceiling

joists to spread the load (mostly me!). Does this sound like a sensible thing to do � ie any better

suggestions?



Nothing wrong with it, but you may be able to get around the problem in

other ways, if you can get a few joists in without needing to load the

existing ceiling too much. Once that is done you can get a temporary

floor to work off and do the rest.

Indeed: Once I get the wall plates on, I'll bring phase 1 of the joists in through the (at that point open) roof, fix the roof timbers, then stash the rest of the floor materials before the roof is sealed again. Then I'll work from that 'platform'. What I'd like to do is avoid wrecking the ceiling at an early stage (!)



One side of the space is an internal wall and the other side is a chimney breast with single-brick party

walls in the recesses each side (these look pretty weak). Each end is the outside wall of the house

running up about 60cm from the ceiling to the eaves of the roof.



So the existing ceiling is not at the top of the wall as such then, but

is suspended a bit below it?


That's right: A bit unusual (and I haven't measured it) but about 2' of vertical wall above the ceiling. Just for a change, something that might make a job easier (famous last words!)


Since the shorter span (about 4m) is

from the internal wall to the chimney breast/party wall, the joists for the new floor will run this way (ie

parallel to the outside walls).



The plan is to use ledger boards (wall plates if you prefer) and joist hangers to mount 50 x 200mm

(-ish) joists at 400mm centres. I know that socketing into the brick is favoured by some but that isn�t

going to happen for many good reasons.



Socketing is rarely done these days it seems... hangers are the norm.



To avoid going near the single-brick party wall, I�ll have to

use trimmers across the (approx.) 1.8m recesses each side of the chimney breast, mounting joist

hangers on these, so this is where the greatest loads will be: With 4 or 5 joists on each trimmer, their

mountings will be carrying approaching 1/3 of the floor loading. The short ledger boards that these trimmers will mount on will, of course, run at 90 degrees to the others (ie along the returns of the

chimney breast and along the outside walls).



You can get strong shoes that rawl bolt to masonry, and are go for 10kN

and more... so one of those at each end of the joist will carry a

significant floor load. I needed to do one like this on my loft at my

previous place.



The bottom left of drawing:



http://internode.co.uk/temp/beam-layout.gif



Shows beam F terminating on one of these shoes. It in effect takes one

end of the entire floor load.


Do you have any details of what you used for that please? They could come in handy here...



So question 2: What�s the panel�s view on the best way to mount the ledger boards, particularly those

that carry the greatest loads? I�m thinking of resin studs between each pair of joist positions (in the

past I would have used expanding bolts but this is Victorian brick), but would a single large stud (M16)

be better or worse than a couple of smaller ones (M12) and is there any benefit in supplementing

these, with anything further (eg a pattern of multi-montis)? For the short ledger boards, I�m thinking

four studs in a rectangle around each joist hanger.

Using more mountings spreads the load, but over-perforating the boards would weaken them (though

I suspect it would take a lot for this to be a big issue).



I can't see much advantage going for M16 over M12 since they are both

going to be significantly stronger than the timber (especially as the

loading is across the grain).



The type of hanger used also makes a difference. With a suitably rigid

one that will not attempt to "unwind" and flip the wall plate over, most

of the load is simply pushing the wall plate hard against the top of the

masonry - there should be very little lateral load.

It seems there's definitely a case for a good snug fit on the joists, which would ensure the forces all resolve in the right directions.




Another option would be the masonry hangers that are designed to be

built into a leaf of brickwork. These can be retrofitted by raking out

some mortar and then mortaring back in. They don't require any bolting

as such.

I had thought of these but sort of dismissed them as it's pretty unlikely that the mortar courses are level enough across the space to end up with a level floor. That may not be a very good excuse nor that I didn't fancy spending too much time up there chiselling out mortar (!) but it just looks like they might not be such a robust fix as the timber mounted ones. I could easily be wrong there.




Lastly, to get decent access into the loft space (currently a 2x2� hatch in a cupboard), I need to create a

new doorway. The only way I can approach this is from the inside of the loft (due to obstructions I

can�t practically re-position until the opening is formed). Normally, cutting a new opening would be

best done using strongboys to support the triangle of brisk above until the lintel is installed but I�d

hesitate to jack against the top of the ceiling and getting them through the hatch wouldn�t be easy.



So question 3: Instead of using strongboys, would a board (4x1 or so) fixed to each brick (multimonti

into the brick centre) above the lintel do an adequate job of stopping everything moving while I get a

lintel in? (A bit non-standard I know, but the best option I can think of in the circumstances!)



That ought to do it. Is this a single leaf or double?


Just a single, so not too much to fall down !


Many thanks for your input John.

Cheers

Installing a loft floor
 

On Wednesday, October 17, 2012 4:05:44 PM UTC+1, Tim Lamb wrote:
In message , John

Rumm writes

On 17/10/2012 11:49, GMM wrote:

Sorry chaps, a bit of a long post but I have tried to get all the

essential information in (!) Undoubtedly

there will be something I've missed out, even so....



Couple of thoughts... someone in here reinforced their existing joists

rather than install new.



The other.. don't allow the new timbers anywhere near the lath and

plaster. We once had a chalet bungalow where the previous owners had

stiffened up the old loft floor to take the new bedrooms load. These

joists spanned the outside walls but were not attached to the old

ceiling ones. Inevitably the new timber moved and pinged nail head

plaster off the downstairs ceiling.



--

Tim Lamb

Absolutely - If there was too much danger of damaging the ceiling, I thin it would make more sense to just take the lot down to start with, then put a floor and new ceiling into the space, which was what the builder did next door in the same place. They were dropping the ceiling height however to accommodate a loft conversion.

Installing a loft floor
 

On Wednesday, October 17, 2012 11:49:06 AM UTC+1, GMM wrote:

I have to build a floor in a loft. At first this will provide a platform for some roof timber repairs to be
carried out but ultimately it will be used for storage, not living space, so there are no formal BR
requirements but, of course, I’d like it to be robust enough that it doesn’t all wind up in the bedroom below.

At present, there is a lath and plaster ceiling, with rather wimpy-looking ceiling joists, so not the most
stable platform to work on. It’s in pretty good condition (as a ceiling, not a floor) so I’d like to keep it

2x8 joists is unusually large for loft storage. Almost all old joists are quite able to handle storage. So I wonder if you've fully and correctly evaluated the situation, ie what the current joist dimensions are (all 3).


NT

Installing a loft floor
 

On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown) wrote:
On Wednesday, October 17, 2012 11:49:06 AM UTC+1, GMM wrote:



I have to build a floor in a loft. At first this will provide a platform for some roof timber repairs to be

carried out but ultimately it will be used for storage, not living space, so there are no formal BR

requirements but, of course, I’d like it to be robust enough that it doesn’t all wind up in the bedroom below.



At present, there is a lath and plaster ceiling, with rather wimpy-looking ceiling joists, so not the most

stable platform to work on. It’s in pretty good condition (as a ceiling, not a floor) so I’d like to keep it



2x8 joists is unusually large for loft storage. Almost all old joists are quite able to handle storage. So I wonder if you've fully and correctly evaluated the situation, ie what the current joist dimensions are (all 3).





NT

Just going by the standard joist span tables for moderately loaded floors. Of courser a lighter joist would be cheaper/easier/more desirable. On the other hand, I'd rather not have the whole thing collapse!

Installing a loft floor
 

On 17/10/2012 20:42, GMM wrote:
On Wednesday, October 17, 2012 3:28:07 PM UTC+1, John Rumm wrote:
On 17/10/2012 11:49, GMM wrote:

The bottom left of drawing:
http://internode.co.uk/temp/beam-layout.gif Shows beam F
terminating on one of these shoes. It in effect takes one end of
the entire floor load.

Do you have any details of what you used for that please? They could
come in handy here...

Its was a masonry fix shoe. In fact there is a picture there of it:

http://internode.co.uk/temp/shoe.jpg

I just had a quick look at the design load, and it was 8.47 kN. From
memory the shoe was rated at 12 or 15 kN.

The type of hanger used also makes a difference. With a suitably
rigid one that will not attempt to "unwind" and flip the wall plate
over, most of the load is simply pushing the wall plate hard
against the top of the masonry - there should be very little
lateral load.

It seems there's definitely a case for a good snug fit on the joists,
which would ensure the forces all resolve in the right directions.

Yup. You could by the sounds of it simply bolt a timber to the wall, and
then nail hangers to that.

Another option would be the masonry hangers that are designed to be
built into a leaf of brickwork. These can be retrofitted by raking
out some mortar and then mortaring back in. They don't require any
bolting as such.

I had thought of these but sort of dismissed them as it's pretty
unlikely that the mortar courses are level enough across the space to
end up with a level floor. That may not be a very good excuse nor
that I didn't fancy spending too much time up there chiselling out
mortar (!) but it just looks like they might not be such a robust fix
as the timber mounted ones. I could easily be wrong there.

Its easy enough to add a timber packer under the beam where it goes into
a shoe to tweak they height it sits in the shoe. For that matter you can
even trim the bottom of the a small amount if needs be.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

wrote:

On Wednesday, October 17, 2012 11:49:06 AM UTC+1, GMM wrote:

I have to build a floor in a loft. At first this will provide a platform
for some roof timber repairs to be carried out but ultimately it will be
used for storage, not living space, so there are no formal BR
requirements but, of course, Id like it to be robust enough that it
doesnt all wind up in the bedroom below.

At present, there is a lath and plaster ceiling, with rather
wimpy-looking ceiling joists, so not the most
stable platform to work on. Its in pretty good condition (as a ceiling,
not a floor) so Id like to keep it

2x8 joists is unusually large for loft storage. Almost all old joists are
quite able to handle storage. So I wonder if you've fully and correctly
evaluated the situation, ie what the current joist dimensions are (all 3).


NT

Did the OP ever say exactly what his current joists were?

--
Tim Watts Personal Blog: http://www.dionic.net/tim/

"History will be kind to me for I intend to write it."

Installing a loft floor
 

In message , Tim Watts
writes
wrote:

On Wednesday, October 17, 2012 11:49:06 AM UTC+1, GMM wrote:

I have to build a floor in a loft. At first this will provide a platform
for some roof timber repairs to be carried out but ultimately it will be
used for storage, not living space, so there are no formal BR
requirements but, of course, Id like it to be robust enough that it
doesnt all wind up in the bedroom below.

At present, there is a lath and plaster ceiling, with rather
wimpy-looking ceiling joists, so not the most
stable platform to work on. Its in pretty good condition (as a ceiling,
not a floor) so Id like to keep it

2x8 joists is unusually large for loft storage. Almost all old joists are
quite able to handle storage. So I wonder if you've fully and correctly
evaluated the situation, ie what the current joist dimensions are (all 3).


NT

Did the OP ever say exactly what his current joists were?

Not that I noticed:-)

The ones holding up our lath and plaster ceiling are around 3"x2".
Raised tie/included attic so about 12' span.


--
Tim Lamb

Installing a loft floor
 

On Wednesday, October 17, 2012 9:57:32 PM UTC+1, Tim Watts wrote:
wrote:



On Wednesday, October 17, 2012 11:49:06 AM UTC+1, GMM wrote:



I have to build a floor in a loft. At first this will provide a platform

for some roof timber repairs to be carried out but ultimately it will be

used for storage, not living space, so there are no formal BR

requirements but, of course, I’d like it to be robust enough that it

doesn’t all wind up in the bedroom below.



At present, there is a lath and plaster ceiling, with rather

wimpy-looking ceiling joists, so not the most

stable platform to work on. It’s in pretty good condition (as a ceiling,

not a floor) so I’d like to keep it



2x8 joists is unusually large for loft storage. Almost all old joists are

quite able to handle storage. So I wonder if you've fully and correctly

evaluated the situation, ie what the current joist dimensions are (all 3).





NT



Did the OP ever say exactly what his current joists were?




The simple answer is there aren't any - apart from the skinny (3x2 or so) ceiling joists. Since these are 150 years old, I wouldn't walk on them without care, let alone base any kind of structure on them.

Installing a loft floor
 

On 17/10/2012 22:50, GMM wrote:

Did the OP ever say exactly what his current joists were?




The simple answer is there aren't any - apart from the skinny (3x2 or so) ceiling joists. Since these are 150 years old, I wouldn't walk on them without care, let alone base any kind of structure on them.


You'll be walking on those when you do the work. Will you support them
temporarily?

Installing a loft floor
 

On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown) wrote:

Just going by the standard joist span tables for moderately loaded floors.. Of courser a lighter joist would be cheaper/easier/more desirable. On the other hand, I'd rather not have the whole thing collapse!

This is a very common misunderstanding. BR requirements are based on sound transmission requirements, producing sizes far in excess of those required for safety. If the table says 2x8 you could use 2x4, fill the loft to the roof, and not be at the remotest risk. A 10' 2x4 can deflect at least 6" safely, a full loft on 10' 2x4s provides a fraction of its safe load limit.

Re noise transmission, the gap between the 2 joist layers has more effect than 2x8s. And I don't expect anyone lives in your loft anyway. :)


NT

Installing a loft floor
 

On 18/10/2012 13:11, wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown) wrote:

Just going by the standard joist span tables for moderately loaded
floors. Of courser a lighter joist would be cheaper/easier/more
desirable. On the other hand, I'd rather not have the whole thing
collapse!

This is a very common misunderstanding. BR requirements are based on
sound transmission requirements, producing sizes far in excess of
those required for safety. If the table says 2x8 you could use 2x4,

They are based on acceptable* levels of deflection rather than sound
transmission (while there are building regs on sound transmission, they
don't figure at all in structural calculations of joist sizes at all as
far as I am aware)

(* Where acceptable is usually specified as a function of the joist
length, or an absolute number of mm if over a certain length. The
calculations will also check that the beam is not likely to fail in
shear at the ends, or bending in the middle)

fill the loft to the roof, and not be at the remotest risk. A 10' 2x4
can deflect at least 6" safely, a full loft on 10' 2x4s provides a
fraction of its safe load limit.

As you highlight, the purpose of the deflection limits is not because
that is where a joist will fail catastrophically, but that is where any
more movement would become unacceptable. L&P ceilings can move a fair
amount, but don't expect one that is supported by a floor structure that
deflects 5 inches every time someone walks over it to last long!


Re noise transmission, the gap between the 2 joist layers has more
effect than 2x8s. And I don't expect anyone lives in your loft
anyway. :)

Loft floors (once strengthened) are actually very good for noise
insulation since they typically have two separate sets of joists
carrying the floor and ceiling loads.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On Thursday, October 18, 2012 1:11:45 PM UTC+1, (unknown) wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:

On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown) wrote:



Just going by the standard joist span tables for moderately loaded floors. Of courser a lighter joist would be cheaper/easier/more desirable. On the other hand, I'd rather not have the whole thing collapse!



This is a very common misunderstanding. BR requirements are based on sound transmission requirements, producing sizes far in excess of those required for safety. If the table says 2x8 you could use 2x4, fill the loft to the roof, and not be at the remotest risk. A 10' 2x4 can deflect at least 6" safely, a full loft on 10' 2x4s provides a fraction of its safe load limit.



Re noise transmission, the gap between the 2 joist layers has more effect than 2x8s. And I don't expect anyone lives in your loft anyway. :)





NT

Well, you're right: Nobody does live in my loft ...at least not that I'm dare of...though you never know
who might sneak in there (according to the Daily Mail at least....(!) I'm anticipating that this floor will
ultimately be loaded with all the junk you normally find in lofts - broken toys, old masters and all that.

On the other hand, I'm not sure it would feel too good to walk on an unsupported 14' span of 2 x 4
and if it deflects 6', then I would have to mount them higher than 2 x 8s so they didn't bang on the
top of the ceiling.

I have been working from the BR tables as a) they would seem to give the best outcome and b) I
couldn't find anything else that gave useful information.

I shall take another look and see if I can find any useful info on this. Perhaps 2 x 6s would do the job
reasonably, although there is an attraction in 2 x 8s in that a future (currently completely off the radar)
loft conversion would be possible without having to take it all down and start again.

Of course, there is an argument that smaller timbers in themselves reduce the total dead weight of the
floor a bit but I should think this is a pretty minor effect as is the impact on overall cost.
Probably the most compelling argument (for me) could be the fact that I have to lug them up 3 floors
to get them in, but that only needs to be done once.

Installing a loft floor
 

GMM wrote:
Sorry chaps, a bit of a long post but I have tried to get all the
essential information in (!) Undoubtedly
there will be something I've missed out, even so....

I have to build a floor in a loft. At first this will provide a
platform for some roof timber repairs to be
carried out but ultimately it will be used for storage, not living
space, so there are no formal BR
requirements but, of course, I'd like it to be robust enough that it
doesn't all wind up in the bedroom below.

At present, there is a lath and plaster ceiling, with rather
wimpy-looking ceiling joists, so not the most
stable platform to work on. It's in pretty good condition (as a
ceiling, not a floor) so I'd like to keep it
that way, which means installing joists clear of the ceiling timbers.
This will, of course, create a void
for a good depth of insulation.

So question 1: To work above the ceiling, I'm thinking of supporting
it with boards on acro jacks,
possibly moving these according to where I'm working as I go and
putting some boards on the ceiling
joists to spread the load (mostly me!). Does this sound like a
sensible thing to do - ie any better
suggestions?

One side of the space is an internal wall and the other side is a
chimney breast with single-brick party
walls in the recesses each side (these look pretty weak). Each end
is the outside wall of the house
running up about 60cm from the ceiling to the eaves of the roof.
Since the shorter span (about 4m) is
from the internal wall to the chimney breast/party wall, the joists
for the new floor will run this way (ie
parallel to the outside walls).

The plan is to use ledger boards (wall plates if you prefer) and
joist hangers to mount 50 x 200mm
(-ish) joists at 400mm centres. I know that socketing into the brick
is favoured by some but that isn't
going to happen for many good reasons. To avoid going near the
single-brick party wall, I'll have to
use trimmers across the (approx.) 1.8m recesses each side of the
chimney breast, mounting joist
hangers on these, so this is where the greatest loads will be: With 4
or 5 joists on each trimmer, their
mountings will be carrying approaching 1/3 of the floor loading. The
short ledger boards that these trimmers will mount on will, of
course, run at 90 degrees to the others (ie along the returns of the
chimney breast and along the outside walls).

So question 2: What's the panel's view on the best way to mount the
ledger boards, particularly those
that carry the greatest loads? I'm thinking of resin studs between
each pair of joist positions (in the
past I would have used expanding bolts but this is Victorian brick),
but would a single large stud (M16)
be better or worse than a couple of smaller ones (M12) and is there
any benefit in supplementing
these, with anything further (eg a pattern of multi-montis)? For the
short ledger boards, I'm thinking
four studs in a rectangle around each joist hanger.
Using more mountings spreads the load, but over-perforating the
boards would weaken them (though
I suspect it would take a lot for this to be a big issue).

Lastly, to get decent access into the loft space (currently a 2x2'
hatch in a cupboard), I need to create a
new doorway. The only way I can approach this is from the inside of
the loft (due to obstructions I
can't practically re-position until the opening is formed).
Normally, cutting a new opening would be
best done using strongboys to support the triangle of brisk above
until the lintel is installed but I'd
hesitate to jack against the top of the ceiling and getting them
through the hatch wouldn't be easy.

So question 3: Instead of using strongboys, would a board (4x1 or
so) fixed to each brick (multimonti
into the brick centre) above the lintel do an adequate job of
stopping everything moving while I get a
lintel in? (A bit non-standard I know, but the best option I can
think of in the circumstances!)

Cheers

Put in the void as much insulation as possible. Also you might want to renew
the lighing cables while you are it, and install more in cae of new light
positions in the romms below. And install some 2.5mm cable ready to fit
sockets up there in case. Even some pipe ready to replace a tank, etc. You
don't want to rip it all up a few years down the line.

Installing a loft floor
 

As you highlight, the purpose of the deflection limits is not because

that is where a joist will fail catastrophically, but that is where any

more movement would become unacceptable. L&P ceilings can move a fair

amount, but don't expect one that is supported by a floor structure that

deflects 5 inches every time someone walks over it to last long!



Not to mention the possibility of seasickness every time anyone bounces around up there !




Re noise transmission, the gap between the 2 joist layers has more

effect than 2x8s. And I don't expect anyone lives in your loft

anyway. :)



Loft floors (once strengthened) are actually very good for noise

insulation since they typically have two separate sets of joists

carrying the floor and ceiling loads.


I'm hoping this one will be good for heat insulation too, with a full load of insulation between the ceiling and the new floor.

Installing a loft floor
 

Put in the void as much insulation as possible. Also you might want to renew

the lighing cables while you are it, and install more in cae of new light

positions in the romms below. And install some 2.5mm cable ready to fit

sockets up there in case. Even some pipe ready to replace a tank, etc. You

don't want to rip it all up a few years down the line.

I couldn't agree mo Flooring over old cable would be a significant error and my first job will be to
put in some decent (and redundant in case one blows) lighting to replace the one batten holder there
at present, along with a socket or two, spurred from a handy point close by.
The (for want of a better term) internal gable end wall is adjacent to the stairs and top floor rooms so
the plan will be to put a layer of celotex over this once I have a floor I can stand on to do it.

Installing a loft floor
 

In article , GB wrote:

The simple answer is there aren't any - apart from the skinny (3x2 or so) ceiling joists. Since these are 150 years old, I wouldn't walk on them without care, let alone base any kind of structure on them.

You'll be walking on those when you do the work. Will you support them
temporarily?

He said he was thinking of boards on Acro props. Knowing exactly which bits
are supported from below when working above might be a bit tricky, but at the
least they'll effectively have a much shorter span.

Installing a loft floor
 

On Thursday, October 18, 2012 5:56:35 PM UTC+1, Alan Braggins wrote:
In article , GB wrote:



The simple answer is there aren't any - apart from the skinny (3x2 or so) ceiling joists. Since these are 150 years old, I wouldn't walk on them without care, let alone base any kind of structure on them.



You'll be walking on those when you do the work. Will you support them

temporarily?



He said he was thinking of boards on Acro props. Knowing exactly which bits

are supported from below when working above might be a bit tricky, but at the

least they'll effectively have a much shorter span.

Quite straightforward really: The loft is exactly the same as the room beneath, so props can be put
directly under the points where work is taking place and moved as it progresses. Using boards above
and below will spread the load.
As you say, even off (but close to) a board this will effectively shorten the span of timber so reduce stresses.
Certainly, in my view, preferable to buggering up the ceiling.

Installing a loft floor
 

On Thursday, October 18, 2012 1:49:59 PM UTC+1, John Rumm wrote:
On 18/10/2012 13:11, meow2222 wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown) wrote:

Just going by the standard joist span tables for moderately loaded
floors. Of courser a lighter joist would be cheaper/easier/more
desirable. On the other hand, I'd rather not have the whole thing
collapse!

This is a very common misunderstanding. BR requirements are based on
sound transmission requirements, producing sizes far in excess of
those required for safety. If the table says 2x8 you could use 2x4,

They are based on acceptable* levels of deflection rather than sound

Whether that's true depends on how you define acceptable. Limiting deflection to 3mm over 10' has absolutely nothing to do with safety or what I would call acceptable deflection limits.


fill the loft to the roof, and not be at the remotest risk. A 10' 2x4
can deflect at least 6" safely, a full loft on 10' 2x4s provides a
fraction of its safe load limit.

As you highlight, the purpose of the deflection limits is not because
that is where a joist will fail catastrophically, but that is where any
more movement would become unacceptable.

Well, not in any sense of acceptable that I would buy into. Lots of old houses have ceiling deflection levels numerous times as big as BR allows, and I don't see any problems or complaints resulting.

L&P ceilings can move a fair
amount, but don't expect one that is supported by a floor structure that
deflects 5 inches every time someone walks over it to last long!

Timber that light isn't being discussed, and the OP's new joists won't be supporting a ceiling.


If 3.1mm deflection would upset the op, go with the tables. I personally wouldnt have any problem with half an inch on a heavily loaded section


NT

Installing a loft floor
 

On Thursday, October 18, 2012 2:17:37 PM UTC+1, GMM wrote:
On Thursday, October 18, 2012 1:11:45 PM UTC+1, (unknown) wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown) wrote:

ultimately be loaded with all the junk you normally find in lofts - broken toys, old masters and all that.

On the other hand, I'm not sure it would feel too good to walk on an unsupported 14' span of 2 x 4
and if it deflects 6', then I would have to mount them higher than 2 x 8s so they didn't bang on the
top of the ceiling.

I regularly put my weight on a single 12' unconnected 2x4, and there's no visible deflection. it helps if you bring reality into this.

In a loft floor structure the joists are connected by the boarding, and sometimes noggings, both of which spread loads over multiple joists


I have been working from the BR tables as a) they would seem to give the best outcome and b) I
couldn't find anything else that gave useful information.

I shall take another look and see if I can find any useful info on this. Perhaps 2 x 6s would do the job
reasonably, although there is an attraction in 2 x 8s in that a future (currently completely off the radar)
loft conversion would be possible without having to take it all down and start again.

Timber requirements get ever deeper as the years roll by.


Probably the most compelling argument (for me) could be the fact that I have to lug them up 3 floors
to get them in, but that only needs to be done once.

Lots of victorian houses have 14' 2x4, 2x3 and even 1.5x3 loft joists, which all support a fully loaded loft without problem.


NT

Installing a loft floor
 

On 18/10/2012 23:56, wrote:
On Thursday, October 18, 2012 1:49:59 PM UTC+1, John Rumm wrote:
On 18/10/2012 13:11, meow2222 wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown)
wrote:

Just going by the standard joist span tables for moderately
loaded floors. Of courser a lighter joist would be
cheaper/easier/more desirable. On the other hand, I'd rather
not have the whole thing collapse!

This is a very common misunderstanding. BR requirements are based
on sound transmission requirements, producing sizes far in excess
of those required for safety. If the table says 2x8 you could use
2x4,

They are based on acceptable* levels of deflection rather than
sound

Whether that's true depends on how you define acceptable. Limiting
deflection to 3mm over 10' has absolutely nothing to do with safety
or what I would call acceptable deflection limits.

(the limit is somewhat higher than 3mm in 10')

However, its not just about safety, but also producing an adequate
quality of building, where the floors don't bounce up and down, and all
the joints crack in the plaster because there is too much movement.

There are other requirements that are also taken into account with the
sizes commonly used, such as minimizing twisting of joists (although
strapping will still be required over 2.5m), and providing lateral
restraint of walls where required.

fill the loft to the roof, and not be at the remotest risk. A 10'
2x4 can deflect at least 6" safely, a full loft on 10' 2x4s
provides a fraction of its safe load limit.

As you highlight, the purpose of the deflection limits is not
because that is where a joist will fail catastrophically, but that
is where any more movement would become unacceptable.

Well, not in any sense of acceptable that I would buy into. Lots of
old houses have ceiling deflection levels numerous times as big as BR
allows, and I don't see any problems or complaints resulting.

I have yet to be in a house where the floor deflects 6" while walking
across a room. Personally I would take that as an indication one should
get out fast!

However it is true that what was acceptable in the past would no longer
meet current standards. That is partly a reflection on more stringent
requirements for air tightness of properties, and also changes in
materials. Lime mortar, and soft bricks will accept more movement than
modern materials for example.

L&P ceilings can move a fair amount, but don't expect one that is
supported by a floor structure that deflects 5 inches every time
someone walks over it to last long!

Timber that light isn't being discussed, and the OP's new joists
won't be supporting a ceiling.

I was responding to your comments about the 2x4 which can deflect 6"
safely rather than the OPs storage floor. A 6" deflection may not cause
it to fail, but it would be excessive by any measure, and would not be
suitable even for loft storage.

The OP can use lighter timbers than those that would be required to meet
the standard of a floor if he wants, although if there was a suggestion
that at some point in the future it was upgraded to a habitable room it
would be sensible to build it to the required standards now obviously.

If 3.1mm deflection would upset the op, go with the tables. I
personally wouldnt have any problem with half an inch on a heavily
loaded section

3.1mm would be fine even for a floor (the limit on that length would be
around 8.4mm IIRC).




--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On 19/10/2012 00:07, wrote:
On Thursday, October 18, 2012 2:17:37 PM UTC+1, GMM wrote:
On Thursday, October 18, 2012 1:11:45 PM UTC+1, (unknown) wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown)
wrote:

Probably the most compelling argument (for me) could be the fact
that I have to lug them up 3 floors to get them in, but that only
needs to be done once.

Lots of victorian houses have 14' 2x4, 2x3 and even 1.5x3 loft
joists, which all support a fully loaded loft without problem.

4x2 joisted lofts usually feel reasonably solid underfoot. However it is
surprising just how much they creep over time, even without too much
weight on them.

If you look at:

http://internode.co.uk/loft/images/sag.jpg

That is looking at a new floor joist over a ceiling supported by 4.2m
4x2" joists.

one of the "D" joists as per:

http://internode.co.uk/temp/beam-layout.gif

The spacing under the ends of the new beam was approx 3/4 to 1" at the
wall plates. Mid span the gap under the joist is getting on for 4" - so
the ceiling had sagged around 3" mid span since when it was originally
built in 1956 (photo taken some time 2004). That was with just light
storage use on chipboard loft panels.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On Friday, October 19, 2012 1:26:36 AM UTC+1, John Rumm wrote:
On 18/10/2012 23:56, meow2222 wrote:
On Thursday, October 18, 2012 1:49:59 PM UTC+1, John Rumm wrote:
On 18/10/2012 13:11, meow2222 wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown)
wrote:

Just going by the standard joist span tables for moderately
loaded floors. Of courser a lighter joist would be
cheaper/easier/more desirable. On the other hand, I'd rather
not have the whole thing collapse!

This is a very common misunderstanding. BR requirements are based
on sound transmission requirements, producing sizes far in excess
of those required for safety. If the table says 2x8 you could use
2x4,

They are based on acceptable* levels of deflection rather than
sound

Whether that's true depends on how you define acceptable. Limiting
deflection to 3mm over 10' has absolutely nothing to do with safety
or what I would call acceptable deflection limits.

(the limit is somewhat higher than 3mm in 10')

However, its not just about safety, but also producing an adequate
quality of building, where the floors don't bounce up and down, and all
the joints crack in the plaster because there is too much movement.

No, its not. Millions of old houses have timber a fraction the size of the current requirements and don't suffer any of those problems.


There are other requirements that are also taken into account with the
sizes commonly used, such as minimizing twisting of joists (although
strapping will still be required over 2.5m), and providing lateral
restraint of walls where required.

fill the loft to the roof, and not be at the remotest risk. A 10'
2x4 can deflect at least 6" safely, a full loft on 10' 2x4s
provides a fraction of its safe load limit.

As you highlight, the purpose of the deflection limits is not
because that is where a joist will fail catastrophically, but that
is where any more movement would become unacceptable.

Well, not in any sense of acceptable that I would buy into. Lots of
old houses have ceiling deflection levels numerous times as big as BR
allows, and I don't see any problems or complaints resulting.

I have yet to be in a house where the floor deflects 6" while walking
across a room. Personally I would take that as an indication one should
get out fast!

obviously that's not relevant

However it is true that what was acceptable in the past would no longer
meet current standards. That is partly a reflection on more stringent
requirements for air tightness of properties,

I've never known a Victorian ceiling/loft floor be draughty

and also changes in
materials. Lime mortar, and soft bricks will accept more movement than
modern materials for example.

Slight movement of loft floor does not move the brickwork. Modern PB is much more tolerant of movement than lath & plaster.


L&P ceilings can move a fair amount, but don't expect one that is
supported by a floor structure that deflects 5 inches every time
someone walks over it to last long!

Timber that light isn't being discussed, and the OP's new joists
won't be supporting a ceiling.

I was responding to your comments about the 2x4 which can deflect 6"
safely rather than the OPs storage floor. A 6" deflection may not cause
it to fail, but it would be excessive by any measure, and would not be
suitable even for loft storage.

Obviously a floor structure that deflects 6" in use has never been proposed. My point was that deflection levels encountered in real life floors are a fraction of failure limits

The OP can use lighter timbers than those that would be required to meet
the standard of a floor if he wants, although if there was a suggestion
that at some point in the future it was upgraded to a habitable room it
would be sensible to build it to the required standards now obviously.

Standards change, so its not obvious, its just an option

If 3.1mm deflection would upset the op, go with the tables. I
personally wouldnt have any problem with half an inch on a heavily
loaded section

3.1mm would be fine even for a floor (the limit on that length would be
around 8.4mm IIRC).


NT

Installing a loft floor
 

On Friday, October 19, 2012 1:35:52 AM UTC+1, John Rumm wrote:
On 19/10/2012 00:07, wrote:
On Thursday, October 18, 2012 2:17:37 PM UTC+1, GMM wrote:
On Thursday, October 18, 2012 1:11:45 PM UTC+1, (unknown) wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown)
wrote:

Probably the most compelling argument (for me) could be the fact
that I have to lug them up 3 floors to get them in, but that only
needs to be done once.

Lots of victorian houses have 14' 2x4, 2x3 and even 1.5x3 loft
joists, which all support a fully loaded loft without problem.

4x2 joisted lofts usually feel reasonably solid underfoot. However it is
surprising just how much they creep over time, even without too much
weight on them.
If you look at:
http://internode.co.uk/loft/images/sag.jpg
That is looking at a new floor joist over a ceiling supported by 4.2m
4x2" joists.
one of the "D" joists as per:
http://internode.co.uk/temp/beam-layout.gif
The spacing under the ends of the new beam was approx 3/4 to 1" at the
wall plates. Mid span the gap under the joist is getting on for 4" - so
the ceiling had sagged around 3" mid span since when it was originally
built in 1956 (photo taken some time 2004). That was with just light
storage use on chipboard loft panels.

That's heavily at variance with my own experiences. I don't know why.


NT

Installing a loft floor
 

On 19/10/2012 13:38, wrote:
On Friday, October 19, 2012 1:26:36 AM UTC+1, John Rumm wrote:
On 18/10/2012 23:56, meow2222 wrote:
On Thursday, October 18, 2012 1:49:59 PM UTC+1, John Rumm wrote:
On 18/10/2012 13:11, meow2222 wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown)
wrote:

Just going by the standard joist span tables for
moderately loaded floors. Of courser a lighter joist would
be cheaper/easier/more desirable. On the other hand, I'd
rather not have the whole thing collapse!

This is a very common misunderstanding. BR requirements are
based on sound transmission requirements, producing sizes far
in excess of those required for safety. If the table says 2x8
you could use 2x4,

They are based on acceptable* levels of deflection rather than
sound

Whether that's true depends on how you define acceptable.
Limiting deflection to 3mm over 10' has absolutely nothing to do
with safety or what I would call acceptable deflection limits.

(the limit is somewhat higher than 3mm in 10')

However, its not just about safety, but also producing an adequate
quality of building, where the floors don't bounce up and down, and
all the joints crack in the plaster because there is too much
movement.

No, its not. Millions of old houses have timber a fraction the size
of the current requirements and don't suffer any of those problems.

True, so long as the fraction you have in mind is say 7/8ths...

Many places in the past would have used say 7x2 where these days 8x2
would be deemed adequate.

There are places which use significantly shallower timbers, but then
tend to have more frequent cross members and hence shorter effective spans.

Many of our downstairs floors here are only on 4x2" joists - but these
span dwarf walls often at 4' spacings - so they are quite rigid.

However it is true that what was acceptable in the past would no
longer meet current standards. That is partly a reflection on more
stringent requirements for air tightness of properties,

I've never known a Victorian ceiling/loft floor be draughty

Modern buildings are in general very much less draughty than Victorian
places. There have been many changes in building practices to achieve
this. One example being joist support. It is no longer common to set
joist ends into openings in walls since (among other things) it also
creates a potential air gap. The switch to joist hangers also frees you
from the limitation of needing to use joist sizes that match a brick
height multiple in height.

and also changes in materials. Lime mortar, and soft bricks will
accept more movement than modern materials for example.

Slight movement of loft floor does not move the brickwork.

I did not say it did - it was an example of building material that is
more tolerant of movement. Perhaps horsehair reinforced plaster would
have been a better example.

Modern PB
is much more tolerant of movement than lath & plaster.

Its different - not necessarily always better.

L&P ceilings can move a fair amount, but don't expect one that
is supported by a floor structure that deflects 5 inches every
time someone walks over it to last long!

Timber that light isn't being discussed, and the OP's new joists
won't be supporting a ceiling.

I was responding to your comments about the 2x4 which can deflect
6" safely rather than the OPs storage floor. A 6" deflection may
not cause it to fail, but it would be excessive by any measure, and
would not be suitable even for loft storage.

Obviously a floor structure that deflects 6" in use has never been
proposed. My point was that deflection levels encountered in real
life floors are a fraction of failure limits

No one (including the building regs) is attempting to suggest otherwise.

The OP can use lighter timbers than those that would be required to
meet the standard of a floor if he wants, although if there was a
suggestion that at some point in the future it was upgraded to a
habitable room it would be sensible to build it to the required
standards now obviously.

Standards change, so its not obvious, its just an option

Indeed, but they rarely reduce, so its fairly obvious (to me at least).

Also building regs are not retrospective. So if a floor was designed as
a floor, and was compliant with the standards of the time, you would be
able to use as the basis of your room in the roof, it even if the
standards applying had changed since it was built.

If 3.1mm deflection would upset the op, go with the tables. I
personally wouldnt have any problem with half an inch on a
heavily loaded section

3.1mm would be fine even for a floor (the limit on that length
would be around 8.4mm IIRC).


NT



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On 19/10/2012 13:40, wrote:
On Friday, October 19, 2012 1:35:52 AM UTC+1, John Rumm wrote:
On 19/10/2012 00:07, wrote:
On Thursday, October 18, 2012 2:17:37 PM UTC+1, GMM wrote:
On Thursday, October 18, 2012 1:11:45 PM UTC+1, (unknown) wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown)
wrote:

Probably the most compelling argument (for me) could be the fact
that I have to lug them up 3 floors to get them in, but that only
needs to be done once.

Lots of victorian houses have 14' 2x4, 2x3 and even 1.5x3 loft
joists, which all support a fully loaded loft without problem.

4x2 joisted lofts usually feel reasonably solid underfoot. However it is
surprising just how much they creep over time, even without too much
weight on them.
If you look at:
http://internode.co.uk/loft/images/sag.jpg
That is looking at a new floor joist over a ceiling supported by 4.2m
4x2" joists.
one of the "D" joists as per:
http://internode.co.uk/temp/beam-layout.gif
The spacing under the ends of the new beam was approx 3/4 to 1" at the
wall plates. Mid span the gap under the joist is getting on for 4" - so
the ceiling had sagged around 3" mid span since when it was originally
built in 1956 (photo taken some time 2004). That was with just light
storage use on chipboard loft panels.

That's heavily at variance with my own experiences. I don't know why.

Its possibly a reflection of the fact its actually quite difficult to
observe a sag of a few inches over a 4m+ span, unless you stick a
straight edge against it like I had in effect done there, or have some
way of sighting along the timber.

The sag was not visible in the room below, although I expect that had
you have gone round with a measuring stick you would have seen it.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On Friday, October 19, 2012 3:53:36 PM UTC+1, John Rumm wrote:
On 19/10/2012 13:38, wrote:
On Friday, October 19, 2012 1:26:36 AM UTC+1, John Rumm wrote:
On 18/10/2012 23:56, meow2222 wrote:
On Thursday, October 18, 2012 1:49:59 PM UTC+1, John Rumm wrote:
On 18/10/2012 13:11, meow2222 wrote:
On Wednesday, October 17, 2012 9:07:08 PM UTC+1, GMM wrote:
On Wednesday, October 17, 2012 8:56:57 PM UTC+1, (unknown)
wrote:


However, its not just about safety, but also producing an adequate
quality of building, where the floors don't bounce up and down, and
all the joints crack in the plaster because there is too much
movement.

No, its not. Millions of old houses have timber a fraction the size
of the current requirements and don't suffer any of those problems.

True, so long as the fraction you have in mind is say 7/8ths...
Many places in the past would have used say 7x2 where these days 8x2
would be deemed adequate.
There are places which use significantly shallower timbers, but then
tend to have more frequent cross members and hence shorter effective spans.

I'm talking about 3, 4 & 5" timber where new builds would use double to triple the size


However it is true that what was acceptable in the past would no
longer meet current standards. That is partly a reflection on more
stringent requirements for air tightness of properties,

I've never known a Victorian ceiling/loft floor be draughty

Modern buildings are in general very much less draughty than Victorian
places. There have been many changes in building practices to achieve
this. One example being joist support. It is no longer common to set
joist ends into openings in walls since (among other things) it also
creates a potential air gap. The switch to joist hangers also frees you
from the limitation of needing to use joist sizes that match a brick
height multiple in height.

But one place draughts don't come in is through Victorian ceilings


The OP can use lighter timbers than those that would be required to
meet the standard of a floor if he wants, although if there was a
suggestion that at some point in the future it was upgraded to a
habitable room it would be sensible to build it to the required
standards now obviously.

Standards change, so its not obvious, its just an option

Indeed, but they rarely reduce, so its fairly obvious (to me at least).
Also building regs are not retrospective. So if a floor was designed as
a floor, and was compliant with the standards of the time, you would be
able to use as the basis of your room in the roof, it even if the
standards applying had changed since it was built.

There's no way a BCO will accept a loft conversion in a 1924 house on its original 3" loft floor joists.


NT

Installing a loft floor
 

On 20/10/2012 01:49, wrote:
On Friday, October 19, 2012 3:53:36 PM UTC+1, John Rumm wrote:
On 19/10/2012 13:38, wrote:

However it is true that what was acceptable in the past would no
longer meet current standards. That is partly a reflection on more
stringent requirements for air tightness of properties,

I've never known a Victorian ceiling/loft floor be draughty

I just noticed that you superficially said *loft* floors there, and my
comments that followed were more generally about "floors" in general -
my fault for not reading carefully.

Modern buildings are in general very much less draughty than Victorian
places. There have been many changes in building practices to achieve
this. One example being joist support. It is no longer common to set
joist ends into openings in walls since (among other things) it also
creates a potential air gap. The switch to joist hangers also frees you
from the limitation of needing to use joist sizes that match a brick
height multiple in height.

But one place draughts don't come in is through Victorian ceilings

There is a general drive to cut down air currents through void spaces in
direct contact with heated surfaces. If you have a penetration through a
wall, then air will flow through it. Even if that never discharges
directly into the living space, it lowers the thermal performance of the
building.

The OP can use lighter timbers than those that would be required to
meet the standard of a floor if he wants, although if there was a
suggestion that at some point in the future it was upgraded to a
habitable room it would be sensible to build it to the required
standards now obviously.

Standards change, so its not obvious, its just an option

Indeed, but they rarely reduce, so its fairly obvious (to me at least).
Also building regs are not retrospective. So if a floor was designed as
a floor, and was compliant with the standards of the time, you would be
able to use as the basis of your room in the roof, it even if the
standards applying had changed since it was built.

There's no way a BCO will accept a loft conversion in a 1924 house on its original 3" loft floor joists.

I doubt a loft with 3" joists would not have been deemed acceptable as a
proper floor for a habitable space - even in 1924.

However, my point was, that if you upgrade something now to the current
standards of a floor in a habitable room, then there would be no need to
upgrade it further if one later made the space habitable - even if the
standards for a floor have changed by then.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On Saturday, October 20, 2012 4:42:00 PM UTC+1, John Rumm wrote:
On 20/10/2012 01:49, wrote:
On Friday, October 19, 2012 3:53:36 PM UTC+1, John Rumm wrote:
On 19/10/2012 13:38, wrote:


Also building regs are not retrospective. So if a floor was designed as
a floor, and was compliant with the standards of the time, you would be
able to use as the basis of your room in the roof, it even if the
standards applying had changed since it was built.

There's no way a BCO will accept a loft conversion in a 1924 house on its original 3" loft floor joists.

I doubt a loft with 3" joists would not have been deemed acceptable as a
proper floor for a habitable space - even in 1924.
However, my point was, that if you upgrade something now to the current
standards of a floor in a habitable room, then there would be no need to
upgrade it further if one later made the space habitable - even if the
standards for a floor have changed by then.

3x3 was the smallest standard habitable flooring joist size in Victorian houses. It was much used for short spans, such as across corridors & landings.

IIRC the 1924 BR didn't specify joist sizes, so 3x3 would still be compliant for habitation then. It could be used in loft floors above corridors, where the span was short.

I challenge you to find any BCO that would accept that in a loft conversion today.


NT

Installing a loft floor
 

On 20/10/2012 20:33, wrote:
On Saturday, October 20, 2012 4:42:00 PM UTC+1, John Rumm wrote:
On 20/10/2012 01:49, wrote:
On Friday, October 19, 2012 3:53:36 PM UTC+1, John Rumm wrote:
On 19/10/2012 13:38, wrote:


Also building regs are not retrospective. So if a floor was
designed as a floor, and was compliant with the standards of
the time, you would be able to use as the basis of your room in
the roof, it even if the standards applying had changed since
it was built.

There's no way a BCO will accept a loft conversion in a 1924
house on its original 3" loft floor joists.

I doubt a loft with 3" joists would not have been deemed acceptable
as a proper floor for a habitable space - even in 1924. However,
my point was, that if you upgrade something now to the current
standards of a floor in a habitable room, then there would be no
need to upgrade it further if one later made the space habitable -
even if the standards for a floor have changed by then.

3x3 was the smallest standard habitable flooring joist size in
Victorian houses. It was much used for short spans, such as across
corridors & landings.

And it still might be acceptable now (for short lengths)

IIRC the 1924 BR didn't specify joist sizes, so 3x3 would still be
compliant for habitation then. It could be used in loft floors above
corridors, where the span was short.

A loft floor is not a floor in the accepted sense though - its not
expected to carry significant load.

I challenge you to find any BCO that would accept that in a loft
conversion today.

A BCO would be happy with a loft using 3x2 - its a good deal better than
many a lofts built with modern trusses. However that is a very different
thing from a loft floor which going to be used for a habitable room. If
you are converting the loft, then the same spec as would apply to any
other floor in the building will kick in.

Out of interest I had an experiment with superbeam to see what you can
get away with on a 3x2 (well 72x47mm) and a typical floor load
(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be about
the limit - so you could probably still do a landing with it and comply
with modern building regs. (having said that, its generally simpler to
use one depth all over to save having to buy lots of timber sizes)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On Saturday, October 20, 2012 10:33:20 PM UTC+1, John Rumm wrote:
On 20/10/2012 20:33, wrote:
On Saturday, October 20, 2012 4:42:00 PM UTC+1, John Rumm wrote:
On 20/10/2012 01:49, wrote:
On Friday, October 19, 2012 3:53:36 PM UTC+1, John Rumm wrote:
On 19/10/2012 13:38, wrote:


Also building regs are not retrospective. So if a floor was
designed as a floor, and was compliant with the standards of
the time, you would be able to use as the basis of your room in
the roof, it even if the standards applying had changed since
it was built.

There's no way a BCO will accept a loft conversion in a 1924
house on its original 3" loft floor joists.

I doubt a loft with 3" joists would not have been deemed acceptable
as a proper floor for a habitable space - even in 1924. However,
my point was, that if you upgrade something now to the current
standards of a floor in a habitable room, then there would be no
need to upgrade it further if one later made the space habitable -
even if the standards for a floor have changed by then.

3x3 was the smallest standard habitable flooring joist size in
Victorian houses. It was much used for short spans, such as across
corridors & landings.

And it still might be acceptable now (for short lengths)

IIRC the 1924 BR didn't specify joist sizes, so 3x3 would still be
compliant for habitation then. It could be used in loft floors above
corridors, where the span was short.

A loft floor is not a floor in the accepted sense though - its not
expected to carry significant load.

I challenge you to find any BCO that would accept that in a loft
conversion today.

A BCO would be happy with a loft using 3x2 - its a good deal better than
many a lofts built with modern trusses. However that is a very different
thing from a loft floor which going to be used for a habitable room. If
you are converting the loft, then the same spec as would apply to any
other floor in the building will kick in.
Out of interest I had an experiment with superbeam to see what you can
get away with on a 3x2 (well 72x47mm) and a typical floor load
(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be about
the limit - so you could probably still do a landing with it and comply
with modern building regs. (having said that, its generally simpler to
use one depth all over to save having to buy lots of timber sizes)

For clarity, lets take it a step further. Say the loft got 2x2s in 4' spans in 1924, hopelessly unsuitable for habitable rooms, but still compliant for them in 1924. So it was built in compliance with BR standards for habitation at the time, and you can indeed walk on them, just about. But no BCO in their right mind would accept a conversion to habitable now on 2x2s.


NT

Installing a loft floor
 

On Sat, 20 Oct 2012 22:33:14 +0100 John Rumm wrote :
Out of interest I had an experiment with superbeam to see what you can
get away with on a 3x2 (well 72x47mm) and a typical floor load
(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be about
the limit - so you could probably still do a landing with it and comply
with modern building regs. (having said that, its generally simpler to
use one depth all over to save having to buy lots of timber sizes)

Our old rule of thumb when I was a BCO which matched the tables pretty
well was that for floor joists double the depth in inches and subtract two
to get the permissible span in feet; flat roof joists, subtract one (2"
joists).

As you say, in most cases practicality requires all joists to be the same
depth (you need tops of joists to be level and want them all to bear on
wall at one level) so except for the largest span they are generally
oversized. There's also more in reserve in that for virtually all joists,
deflection governs the size, not bending stress and few floors are loaded
to BR design loads (1.5kN/m2 30lb/ft2).

--
Tony Bryer, Greentram: 'Software to build on',
Melbourne, Australia www.greentram.com

Installing a loft floor
 

On 21/10/2012 08:13, Tim Lamb wrote:
In message , Tony Bryer
writes
On Sat, 20 Oct 2012 22:33:14 +0100 John Rumm wrote :
Out of interest I had an experiment with superbeam to see what you can
get away with on a 3x2 (well 72x47mm) and a typical floor load
(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be about
the limit - so you could probably still do a landing with it and comply
with modern building regs. (having said that, its generally simpler to
use one depth all over to save having to buy lots of timber sizes)

Our old rule of thumb when I was a BCO which matched the tables pretty
well was that for floor joists double the depth in inches and subtract
two
to get the permissible span in feet; flat roof joists, subtract one (2"
joists).

As you say, in most cases practicality requires all joists to be the same
depth (you need tops of joists to be level and want them all to bear on
wall at one level) so except for the largest span they are generally
oversized. There's also more in reserve in that for virtually all joists,
deflection governs the size, not bending stress and few floors are loaded
to BR design loads (1.5kN/m2 30lb/ft2).

Slightly sideways... is it possible that the quality of timber available
to the Victorians was better than that of today?

I use a lot of recycled 4"x2" and generally find that the grain is more
dense and the knots smaller than that supplied new.



A dense grain means a timber gown in more northerly climes, and I don't
think the climate has changed significantly since Victorian times. There
has always been, and still is, a great variation in quality and price
for what is loosely termed "4x2"

Installing a loft floor
 

On Sun, 21 Oct 2012 08:13:13 +0100, Tim Lamb
wrote:

Slightly sideways... is it possible that the quality of timber available
to the Victorians was better than that of today?

I use a lot of recycled 4"x2" and generally find that the grain is more
dense and the knots smaller than that supplied new.

Most timber Victorians used in buildings would have been imported and
Baltic or Scandinavian, slow grown 14 rings to the inch and the snow
load knocks off dead suppressed branches.

We were major importers of wood on the global market as our economy
grew earlier than others.

Since the 1950s more home grown timber has come on line and it has
benefited from machine stress grading where in the past it failed
visual grading. Also I suspect much Canadian lumber is second growth
nowadays.


AJH

Installing a loft floor
 

On 21/10/2012 11:13, wrote:
On Sun, 21 Oct 2012 08:13:13 +0100, Tim Lamb
wrote:

Slightly sideways... is it possible that the quality of timber available
to the Victorians was better than that of today?

I use a lot of recycled 4"x2" and generally find that the grain is more
dense and the knots smaller than that supplied new.

Most timber Victorians used in buildings would have been imported and
Baltic or Scandinavian, slow grown 14 rings to the inch and the snow
load knocks off dead suppressed branches.

Interesting about the snow.


We were major importers of wood on the global market as our economy
grew earlier than others.

Since the 1950s more home grown timber has come on line and it has
benefited from machine stress grading where in the past it failed
visual grading. Also I suspect much Canadian lumber is second growth
nowadays.


AJH


Finnish softwood is as good as it's ever been but too pricey for the
general market

Installing a loft floor
 

On Sunday, October 21, 2012 2:16:39 AM UTC+1, Tony Bryer wrote:
On Sat, 20 Oct 2012 22:33:14 +0100 John Rumm wrote :

Out of interest I had an experiment with superbeam to see what you can

get away with on a 3x2 (well 72x47mm) and a typical floor load

(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be about

the limit - so you could probably still do a landing with it and comply

with modern building regs. (having said that, its generally simpler to

use one depth all over to save having to buy lots of timber sizes)



Our old rule of thumb when I was a BCO which matched the tables pretty

well was that for floor joists double the depth in inches and subtract two

to get the permissible span in feet; flat roof joists, subtract one (2"

joists).



As you say, in most cases practicality requires all joists to be the same

depth (you need tops of joists to be level and want them all to bear on

wall at one level) so except for the largest span they are generally

oversized. There's also more in reserve in that for virtually all joists,

deflection governs the size, not bending stress and few floors are loaded

to BR design loads (1.5kN/m2 30lb/ft2).



--

Tony Bryer, Greentram: 'Software to build on',

Melbourne, Australia www.greentram.com

So for a 14ft span (as here), the 8" joists I originally proposed would be about right?
I wonder if the tables are constructed from that rule of thumb or from a complex calculation that gives the same result?
I guess most of the discussion (now) is about what you might be able to get away with, rather than what should be done, but I'd prefer to over-engineer than under, for the sake of a couple inches.
Of course, I'm equally concerned that they are mounted securely, as Mr R outlined......

Installing a loft floor
 

On 21/10/2012 00:37, wrote:
On Saturday, October 20, 2012 10:33:20 PM UTC+1, John Rumm wrote:
On 20/10/2012 20:33, wrote:
On Saturday, October 20, 2012 4:42:00 PM UTC+1, John Rumm wrote:
On 20/10/2012 01:49, wrote:
On Friday, October 19, 2012 3:53:36 PM UTC+1, John Rumm
wrote:
On 19/10/2012 13:38, wrote:


Also building regs are not retrospective. So if a floor
was designed as a floor, and was compliant with the
standards of the time, you would be able to use as the
basis of your room in the roof, it even if the standards
applying had changed since it was built.

There's no way a BCO will accept a loft conversion in a 1924
house on its original 3" loft floor joists.

I doubt a loft with 3" joists would not have been deemed
acceptable as a proper floor for a habitable space - even in
1924. However, my point was, that if you upgrade something now
to the current standards of a floor in a habitable room, then
there would be no need to upgrade it further if one later made
the space habitable - even if the standards for a floor have
changed by then.

3x3 was the smallest standard habitable flooring joist size in
Victorian houses. It was much used for short spans, such as
across corridors & landings.

And it still might be acceptable now (for short lengths)

IIRC the 1924 BR didn't specify joist sizes, so 3x3 would still
be compliant for habitation then. It could be used in loft floors
above corridors, where the span was short.

A loft floor is not a floor in the accepted sense though - its not
expected to carry significant load.

I challenge you to find any BCO that would accept that in a loft
conversion today.

A BCO would be happy with a loft using 3x2 - its a good deal better
than many a lofts built with modern trusses. However that is a very
different thing from a loft floor which going to be used for a
habitable room. If you are converting the loft, then the same spec
as would apply to any other floor in the building will kick in. Out
of interest I had an experiment with superbeam to see what you can
get away with on a 3x2 (well 72x47mm) and a typical floor load
(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be
about the limit - so you could probably still do a landing with it
and comply with modern building regs. (having said that, its
generally simpler to use one depth all over to save having to buy
lots of timber sizes)

For clarity, lets take it a step further. Say the loft got 2x2s in 4'
spans in 1924, hopelessly unsuitable for habitable rooms, but still
compliant for them in 1924.

I don't think 2x2 would have been used for the floor of a habitable room
in 1924 or at any other time.

Its seems to are engaging in a little reductio ad absurdum.

So it was built in compliance with BR
standards for habitation at the time, and you can indeed walk on
them, just about. But no BCO in their right mind would accept a
conversion to habitable now on 2x2s.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Installing a loft floor
 

On 21/10/2012 08:13, Tim Lamb wrote:
In message , Tony Bryer
writes
On Sat, 20 Oct 2012 22:33:14 +0100 John Rumm wrote :
Out of interest I had an experiment with superbeam to see what you can
get away with on a 3x2 (well 72x47mm) and a typical floor load
(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be about
the limit - so you could probably still do a landing with it and comply
with modern building regs. (having said that, its generally simpler to
use one depth all over to save having to buy lots of timber sizes)

Our old rule of thumb when I was a BCO which matched the tables pretty
well was that for floor joists double the depth in inches and subtract
two
to get the permissible span in feet; flat roof joists, subtract one (2"
joists).

As you say, in most cases practicality requires all joists to be the same
depth (you need tops of joists to be level and want them all to bear on
wall at one level) so except for the largest span they are generally
oversized. There's also more in reserve in that for virtually all joists,
deflection governs the size, not bending stress and few floors are loaded
to BR design loads (1.5kN/m2 30lb/ft2).

Slightly sideways... is it possible that the quality of timber available
to the Victorians was better than that of today?

Almost certainly... it may not have been "stress graded" but then it was
not the fast grown, low density, twisted to buggery stuff that often
masquerades as timber these days.

I use a lot of recycled 4"x2" and generally find that the grain is more
dense and the knots smaller than that supplied new.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/