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Dave Page
 
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Default Raising Roof Joists for Loft Flooring

I am planning on insulating my loft to the recommended 270mm, and would
also like to lay floorboards above the insulation so I can keep using
the loft for storage. The gap between the ceiling and the top of the
existing joists is 70mm, so there's 200mm to go.

I'm intending on adding two strips of 40 x 100 on top of the existing
joists, screwing them down, and laying the insulation between them and
boards on top. It seems like a fairly simple job.

There's one bit of information I'm missing; what sort of timber would be
appropriate for this job?

Dave
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Lobster
 
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Default Raising Roof Joists for Loft Flooring

Dave Page wrote:
I am planning on insulating my loft to the recommended 270mm, and would
also like to lay floorboards above the insulation so I can keep using
the loft for storage. The gap between the ceiling and the top of the
existing joists is 70mm, so there's 200mm to go.

I'm intending on adding two strips of 40 x 100 on top of the existing
joists, screwing them down, and laying the insulation between them and
boards on top. It seems like a fairly simple job.


When topping up old insulation (Rockwool) it's normal and more effective
to lay the second layer perpendicular to the first. So you'd be better
off fitting the new joists perpendicular to the originals I'd have
thought. However, your original ceiling joists are not very meaty, so
depending on the span, you may have a problem there, if you are going to
pile lots of new joists, floorboards and storage items up there.

There's one bit of information I'm missing; what sort of timber would be
appropriate for this job?


Just bog standard timber joists from the timber yard - haven't a clue
what species it is!

David
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Dave Page
 
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Default Raising Roof Joists for Loft Flooring

Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.


I was intending to replace the existing insulation - it's only about an
inch thick, dead old (over 10 years), and patchily installed. Plus
insulation seems to come (from Wickes at least, who are selling rolls ad
near-half-price until this weekend) in 170mm and 100mm depths.

So you'd be better off fitting the new joists perpendicular to the
originals I'd have thought. However, your original ceiling joists
are not very meaty, so depending on the span, you may have a problem
there, if you are going to pile lots of new joists, floorboards and
storage items up there.


The joists are 14" / 355mm apart, so there are plenty of them (this is
particularly annoying since insulation roll seems to come in 400mm
widths). The thought of laying new joists crosswise is interesting, not
least because it would save me a few screws.

As it was, I'm not planning on putting too much weight up there, and was
considering only raising every other joist to save on timber. On the
other hand, the loft hatch is only 750mm wide, so if I want the boards
to be supported by three joists, I'll need to space the joists at
roughly 350mm anyway

There's one bit of information I'm missing; what sort of timber
would be appropriate for this job?


Just bog standard timber joists from the timber yard - haven't a clue
what species it is!


That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m
lengths, I'll ask someone at the store whether it's suitable for my
purposes if it works out cheaper than a timber merchant.

Dave
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The Natural Philosopher
 
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Default Raising Roof Joists for Loft Flooring

Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more effective
to lay the second layer perpendicular to the first.


I think you mean 'orthogonal'

Perpendicular is walls... ;-)
  #5   Report Post  
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Ian Stirling
 
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Default Raising Roof Joists for Loft Flooring

The Natural Philosopher wrote:
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more effective
to lay the second layer perpendicular to the first.


I think you mean 'orthogonal'

Perpendicular is walls... ;-)


Umm, no.
Perpendicular can also mean simply "a straight line at right angles to
another line".



  #6   Report Post  
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The Natural Philosopher
 
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Default Raising Roof Joists for Loft Flooring

Ian Stirling wrote:
The Natural Philosopher wrote:
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more effective
to lay the second layer perpendicular to the first.

I think you mean 'orthogonal'

Perpendicular is walls... ;-)


Umm, no.
Perpendicular can also mean simply "a straight line at right angles to
another line".


....that is laying horizontal.

Orthogonal is better. Less implications of verticality.,
  #7   Report Post  
Posted to uk.d-i-y
Dave Page
 
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Default Raising Roof Joists for Loft Flooring

The Natural Philosopher wrote:
Lobster wrote:


When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.


I think you mean 'orthogonal'


Perpendicular is walls... ;-)


I understood what Lobster meant, and feel that "perpendicular" was quite
appropriate. After all, laying insulation foam vertically wouldn't make
sense.

Dave
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Posted to uk.d-i-y
Lobster
 
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Default Raising Roof Joists for Loft Flooring

Dave Page wrote:
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.


I was intending to replace the existing insulation - it's only about an
inch thick, dead old (over 10 years), and patchily installed. Plus
insulation seems to come (from Wickes at least, who are selling rolls ad
near-half-price until this weekend) in 170mm and 100mm depths.


I wouldn't bother lifting the old stuff - 'orrible job, and it won't do
any harm being added to by what you're going to lay on top. I've used
the Wickes stuff; it's still intended to be laid perpendicularly (or
orthogonally - FFS!) even if you're starting from scratch (I think their
instruction sheet says so).

There's one bit of information I'm missing; what sort of timber would
be appropriate for this job?


Just bog standard timber joists from the timber yard - haven't a clue
what species it is!


That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m
lengths, I'll ask someone at the store whether it's suitable for my
purposes if it works out cheaper than a timber merchant.


That's just the job, their 'kiln-dried', unfinished stuff is what you
want, with the purple sticker! Look down its length to check it's
straight before you put it on your trolley; especially if they haven't
got much stock in, a lot of it can be banana-shaped. Personally, I find
Wickes cheaper than timber yards as they won't give me decent trade prices.

Still not too happy about your weight issue though, but I could be wrong
- hopefully someone with more knowledge than me will comment?

David
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John Cartmell
 
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Default Raising Roof Joists for Loft Flooring

In article ,
Dave Page wrote:
The Natural Philosopher wrote:
Lobster wrote:


When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.


I think you mean 'orthogonal'


Perpendicular is walls... ;-)


I understood what Lobster meant, and feel that "perpendicular" was quite
appropriate. After all, laying insulation foam vertically wouldn't make
sense.


'Perpendicular' without the sense of vertical makes no sense at all. What
would it be hanging (-pend-) from?

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing

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Lobster
 
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Default Raising Roof Joists for Loft Flooring

Dave Page wrote:
The Natural Philosopher wrote:

Lobster wrote:



When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.



I think you mean 'orthogonal'



Perpendicular is walls... ;-)



I understood what Lobster meant, and feel that "perpendicular" was quite
appropriate.


Ah, but would you have understood if I'd said "orthogonal"? :-)

David


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Posted to uk.d-i-y
Dave Page
 
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Default Raising Roof Joists for Loft Flooring

Lobster wrote:
Dave Page wrote:


I understood what Lobster meant, and feel that "perpendicular" was
quite appropriate.


Ah, but would you have understood if I'd said "orthogonal"? :-)


Probably, yes. Or even "crossways".

Dave
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Bob Mannix
 
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Default Raising Roof Joists for Loft Flooring


"John Cartmell" wrote in message
...
In article ,
Dave Page wrote:
The Natural Philosopher wrote:
Lobster wrote:


When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.


I think you mean 'orthogonal'


Perpendicular is walls... ;-)


I understood what Lobster meant, and feel that "perpendicular" was quite
appropriate. After all, laying insulation foam vertically wouldn't make
sense.


'Perpendicular' without the sense of vertical makes no sense at all. What
would it be hanging (-pend-) from?


Yes it does. It only implies vertical in some of its meanings (architecture,
physical landscape) and not in others (maths and the conjunction of two
lines or planes).

A quote from Round the World in Eighty Days:

"It was supplied with two rows of seats, perpendicular to the direction of
the train on either side of an aisle which conducted to the front and rear
platforms."

Orthogonal could just as easily be vertical or horizontal as well.

Of course one could have used "at right angles to" )


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)


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John Cartmell
 
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Default Raising Roof Joists for Loft Flooring

In article ,
Lobster wrote:
Dave Page wrote:
The Natural Philosopher wrote:


Lobster wrote:


When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.


I think you mean 'orthogonal'


Perpendicular is walls... ;-)


I understood what Lobster meant, and feel that "perpendicular" was quite
appropriate.


Ah, but would you have understood if I'd said "orthogonal"? :-)


As a board game designer - yes! I use it in practically every set of rules
that I produce ...


... but feel obliged to define it every time! ;-)

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing

  #14   Report Post  
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Ian Stirling
 
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Default Raising Roof Joists for Loft Flooring

Dave Page wrote:
The Natural Philosopher wrote:
Lobster wrote:


When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.


I think you mean 'orthogonal'


Perpendicular is walls... ;-)


I understood what Lobster meant, and feel that "perpendicular" was quite
appropriate. After all, laying insulation foam vertically wouldn't make
sense.


It would - but it tends to slide off
I'm wondering ATM if any of the common '270mm' rolls of stuff on the
market can be split into 3 or 4 parts - for insulating the garage.
  #15   Report Post  
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Dave Page
 
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Default Raising Roof Joists for Loft Flooring

Lobster wrote:
Dave Page wrote:


I was intending to replace the existing insulation - it's only
about an inch thick, dead old (over 10 years), and patchily
installed. Plus insulation seems to come (from Wickes at least, who
are selling rolls ad near-half-price until this weekend) in 170mm
and 100mm depths.


I wouldn't bother lifting the old stuff - 'orrible job, and it won't
do any harm being added to by what you're going to lay on top.


Frankly, it's all I can do to stop it blowing away in a draft.

I've used the Wickes stuff; it's still intended to be laid
perpendicularly (or orthogonally - FFS!) even if you're starting from
scratch (I think their instruction sheet says so).


Fair enough. In that case, I'm not sure what the best thing to do is; if
I lay the insulation perpendicular to the existing joists, I'm not going
to be able to get 270mm down over the existing joints (or a little way
either side) unless I lay *more* joisting over the top. Seems the best
thing to do might be to lay down the 100mm rolls *between* the existing
joists, lay another 200mm of joisting perpendicular to that (squishing
down some of the insulation beneath), and rolling the 170mm insulation
between the new joisting.

Still not too happy about your weight issue though, but I could be
wrong - hopefully someone with more knowledge than me will comment?


Well, if there's concern, I'll hold off for a little while until
consensus forms. Can't wait too long though, I want to make the purchase
before the Wickes special offer on insulation ends on Saturday, and I'm
busy all day Friday.

Dave


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Bob Mannix
 
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Default Raising Roof Joists for Loft Flooring


"John Cartmell" wrote in message
...
In article ,
Bob Mannix wrote:

"John Cartmell" wrote in message
...
In article ,
Dave Page wrote:
The Natural Philosopher wrote:
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.

I think you mean 'orthogonal'

Perpendicular is walls... ;-)

I understood what Lobster meant, and feel that "perpendicular" was
quite
appropriate. After all, laying insulation foam vertically wouldn't
make
sense.

'Perpendicular' without the sense of vertical makes no sense at all.
What
would it be hanging (-pend-) from?


Yes it does. It only implies vertical in some of its meanings
(architecture,
physical landscape) and not in others (maths and the conjunction of two
lines or planes).


AFAIK it should only be used in maths & drawing where it's used to
represent a
physical verticality.


Oh no, definitely not - two lines in maths/geometry perpendicular to each
other are usually representing no physical reality at all but are always
described as perpendicular

Where you are describing a physical (3 or more
dimensions) situation 'perpendicular' cannot mean horizontal.


It cannot *mean* horizontal per se, I agree, but could be used to describe
things which form lines at right angles in some arbitrary plane (which might
be horizontal) by considering them merely as geometric concepts. If the
information being conveyed included information on verticality then
perpendicular would clearly mean vertical.


A quote from Round the World in Eighty Days:


"It was supplied with two rows of seats, perpendicular to the direction
of
the train on either side of an aisle which conducted to the front and
rear
platforms."


The translator made an error.


That one's for a rainy day, I fear, not having a French copy to hand )


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)


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John Cartmell
 
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Default Raising Roof Joists for Loft Flooring

In article , Bob Mannix
wrote:

"John Cartmell" wrote in message
...
In article , Bob Mannix
wrote:

"John Cartmell" wrote in message
...
In article , Dave Page
wrote:
The Natural Philosopher wrote:
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.

I think you mean 'orthogonal'

Perpendicular is walls... ;-)

I understood what Lobster meant, and feel that "perpendicular" was
quite appropriate. After all, laying insulation foam vertically
wouldn't make sense.

'Perpendicular' without the sense of vertical makes no sense at all.
What would it be hanging (-pend-) from?


Yes it does. It only implies vertical in some of its meanings
(architecture, physical landscape) and not in others (maths and the
conjunction of two lines or planes).


AFAIK it should only be used in maths & drawing where it's used to
represent a physical verticality.


Oh no, definitely not - two lines in maths/geometry perpendicular to each
other are usually representing no physical reality at all but are always
described as perpendicular


No.
You have to define the horizontal plane first. Of course that may only be
assumed but, if you have assumed a line across the page to be the horizon and
the top of the page as up, then a line at right angles to the first line is
perpendicular to it *because you have defined the first line as the horizon*.
In lazy maths today we generally forget that we have implicitly made that
initial assumption.

Where you are describing a physical (3 or more dimensions) situation
'perpendicular' cannot mean horizontal.


It cannot *mean* horizontal per se, I agree, but could be used to describe
things which form lines at right angles in some arbitrary plane (which
might be horizontal) by considering them merely as geometric concepts. If
the information being conveyed included information on verticality then
perpendicular would clearly mean vertical.


You can indeed make any arbitrary plane the horizontal plane. In the case in
hand you are saying that you have assumed that a vertical plane through the
house is the horizontal plane.

Can we please return to reality before the thought makes me sea-sick! ;-)

A quote from Round the World in Eighty Days:


"It was supplied with two rows of seats, perpendicular to the direction
of the train on either side of an aisle which conducted to the front and
rear platforms."


The translator made an error.


That one's for a rainy day, I fear, not having a French copy to hand )


http://www.fourmilab.ch/etexts/www/tdm80j/tdm80j.html

;-)

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing

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Ian Stirling
 
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Default Raising Roof Joists for Loft Flooring

Bob Mannix wrote:
snip
Oh no, definitely not - two lines in maths/geometry perpendicular to each
other are usually representing no physical reality at all but are always
described as perpendicular


Normally.
  #19   Report Post  
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Dave Page
 
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Default Raising Roof Joists for Loft Flooring

Weatherlawyer wrote:

I am planning on insulating my loft to the recommended 270mm, and
would also like to lay floorboards above the insulation so I can
keep using the loft for storage. The gap between the ceiling and
the top of the existing joists is 70mm, so there's 200mm to go.


First thing get the cheapest offer you can with the insulation. But
for heaven's sake phone around all the other places too first.
Builders merchants not only stock it they deiver.


Wickes deliver too, for a small fee. I'm not sure where all these "other
places" are. I don't know any reputable builder's merchants, and
wouldn't know how to tell if one *were* reputable. Wickes was
recommended to me by the nice man who did my central heating, and did a
very nice job of it too.

Secondly, why are you intent on adding timber? If you must walk
around up there for maintainance in the future all you need is a
walkway built up. If that. You could just lay a plank or two over the
wool.


As mentioned in my original post:

would also like to lay floorboards above the insulation so I can
keep using the loft for storage.


That's why I'm intent on adding timber

Remember there must be a draught in the roof at all times as the
amount of moisture that vents through it is quite amazing.


Yep, I wasn't going to lay the insulation all the way to the eaves, or
to the ceiling.

Third: However much you put up there at first, it will have shrunk to
a lot less after a few months settlement. Talk it over with the
salesmen in the timberyards you get quotes from. They will be far
more knowledgeable than staff at Wickes's or similar. Though I must
admit a few B&Q staffers I have met seemed on the ball.


Bugger, this was the sort of thing I was worried about. Will I need to
stick the timber up in the loft for a few months until it adjusts to the
weather conditions up there before I can cut and fit it?

Dave
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John Cartmell
 
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Default Raising Roof Joists for Loft Flooring

In article ,
Ian Stirling wrote:
Bob Mannix wrote:
snip
Oh no, definitely not - two lines in maths/geometry perpendicular to each
other are usually representing no physical reality at all but are always
described as perpendicular


Normally.


I do hope that was meant mathematically! ;-)

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing



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The Natural Philosopher
 
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Default Raising Roof Joists for Loft Flooring

Dave Page wrote:
Lobster wrote:
Dave Page wrote:


I understood what Lobster meant, and feel that "perpendicular" was
quite appropriate.


Ah, but would you have understood if I'd said "orthogonal"? :-)


Probably, yes. Or even "crossways".

Dave


Crossways is good.

Plain Builders English.
  #22   Report Post  
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The Natural Philosopher
 
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Default Raising Roof Joists for Loft Flooring

Bob Mannix wrote:

Orthogonal could just as easily be vertical or horizontal as well.

Of course one could have used "at right angles to" )

Orthogonal means 'at right angles to'

  #23   Report Post  
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Doctor Drivel
 
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Default Raising Roof Joists for Loft Flooring


"Dave Page" wrote in message
...
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more effective
to lay the second layer perpendicular to the first.


I was intending to replace the existing insulation - it's only about an
inch thick, dead old (over 10 years), and patchily installed. Plus
insulation seems to come (from Wickes at least, who are selling rolls ad
near-half-price until this weekend) in 170mm and 100mm depths.

So you'd be better off fitting the new joists perpendicular to the
originals I'd have thought. However, your original ceiling joists are
not very meaty, so depending on the span, you may have a problem there,
if you are going to pile lots of new joists, floorboards and storage
items up there.


The joists are 14" / 355mm apart, so there are plenty of them (this is
particularly annoying since insulation roll seems to come in 400mm
widths). The thought of laying new joists crosswise is interesting, not
least because it would save me a few screws.

As it was, I'm not planning on putting too much weight up there, and was
considering only raising every other joist to save on timber. On the other
hand, the loft hatch is only 750mm wide, so if I want the boards to be
supported by three joists, I'll need to space the joists at roughly 350mm
anyway


Lay the joists at right angles and use joist hangers where they meet the
walls if any (gable end). Use 6" screws. Unifix supply these quite cheap.
Having the at 90 degrees reduces thermal bridging enormously.

There's one bit of information I'm missing; what sort of timber would be
appropriate for this job?


Just bog standard timber joists from the timber yard - haven't a clue
what species it is!


That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m
lengths, I'll ask someone at the store whether it's suitable for my
purposes if it works out cheaper than a timber merchant.

Dave


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Doctor Drivel
 
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Default Raising Roof Joists for Loft Flooring


"Weatherlawyer" wrote in message
oups.com...

Dave Page wrote:
I am planning on insulating my loft to the recommended 270mm, and would
also like to lay floorboards above the insulation so I can keep using
the loft for storage. The gap between the ceiling and the top of the
existing joists is 70mm, so there's 200mm to go.

I'm intending on adding two strips of 40 x 100 on top of the existing
joists, screwing them down, and laying the insulation between them and
boards on top. It seems like a fairly simple job.

There's one bit of information I'm missing; what sort of timber would be
appropriate for this job?

First thing get the cheapest offer you can with the insulation. But for
heaven's sake phone around all the other places too first. Builders
merchants not only stock it they deiver.

Secondly, why are you intent on adding timber? If you must walk around
up there for maintainance in the future all you need is a walkway built
up. If that. You could just lay a plank or two over the wool.

The rolls of insulate come in bags of three, sometimes you have to cut
them apart. But if you lay them crosswise over the beams you can lay a
full three rolls at a time.

Remember there must be a draught
in the roof at all times as the amount
of moisture that vents through it
is quite amazing.


As he is removing the old insulation, it is best seal up the holes where
cable and pipes penetrate with silicon, then lat a poly vapour barrier on
the plasterboard/joist. Pin it with a staple gun to side of the joists and
tape the joins with big overlaps. Then lay the insulation and lay the new
joists. Then make sure the hatch is sealed and insulated too.


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Posted to uk.d-i-y
 
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Default Raising Roof Joists for Loft Flooring

Doctor Drivel wrote:
"Dave Page" wrote in message
...
Lobster wrote:


I was intending to replace the existing insulation - it's only about an
inch thick, dead old (over 10 years), and patchily installed. Plus
insulation seems to come (from Wickes at least, who are selling rolls ad
near-half-price until this weekend) in 170mm and 100mm depths.


The joists are 14" / 355mm apart, so there are plenty of them (this is
particularly annoying since insulation roll seems to come in 400mm
widths). The thought of laying new joists crosswise is interesting, not
least because it would save me a few screws.

As it was, I'm not planning on putting too much weight up there, and was
considering only raising every other joist to save on timber. On the other
hand, the loft hatch is only 750mm wide, so if I want the boards to be
supported by three joists, I'll need to space the joists at roughly 350mm
anyway


That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m
lengths, I'll ask someone at the store whether it's suitable for my
purposes if it works out cheaper than a timber merchant.

Dave



Lets review the options.

1. Lay new joists on old at 90 degrees
This will leave you with a very weak floor, as well as being a pain to
insulate.

2. Lay new joists at 90 degrees on joist hangers into the walls
This is illegal in a lot of properties under the Party Wall Act, and
might get you into a bundle of trouble.

3. Add new 4x2 joists to the top of the old ones, inline, attaching
with glue and screws.
This is legal, and will bring a dramatic increase in strength to your
floor/ceiling structure, enabling you to stack goods to the roof
without worry of collapse, distortion, etc.
When joining timbers, (since it isnt easy to get a full length one in
there) the structure will be stronger if you glue joint them rather
than just butt them, but eiher will help.
Laying insulation is easy.

4. Add new wood on every other joist
This will cause damage to the ceiling, as the differing loads will try
to mildly corrugate the non-flexible plaster ceiling. Expect cracking
and damage.

Any 2x4 will do, as long as its straight. Spruce aka whitewood is
cheapest.


NT



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Ian White
 
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Default Raising Roof Joists for Loft Flooring


Add new 4x2 joists to the top of the old ones, inline, attaching with
glue and screws. This is legal, and will bring a dramatic increase in
strength to your floor/ceiling structure,


This is a well accepted method when the existing ceiling rafters are
already almost deep enough.

The aim of gluing and screwing the two parts together is to prevent the
composite beam from bending by one part sliding over the other. The glue
is much more important than the screws because the large bond area
distributes the shear forces more evenly. The main contribution of the
screws is to help make a good glue bond, and afterwards they are almost
incidental.

In loft conversions, this is usually supplemented by glueing and
screwing the chipboard floor down, which adds yet more stiffness to the
whole structure.



--
Ian White
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Rob Morley
 
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Default Raising Roof Joists for Loft Flooring

In article
Dave Page wrote:
snip
As it was, I'm not planning on putting too much weight up there, and was
considering only raising every other joist to save on timber.


That means the load on the loft floor would only be supported by half of
the joists, and the boards would be spanning a considerable gap -
neither of these is a good thing.

On the
other hand, the loft hatch is only 750mm wide, so if I want the boards
to be supported by three joists, I'll need to space the joists at
roughly 350mm anyway

The boards go across the joists, not along them.
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Rob Morley
 
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Default Raising Roof Joists for Loft Flooring

In article
Bob Mannix wrote:
snip
Oh no, definitely not - two lines in maths/geometry perpendicular to each
other are usually representing no physical reality at all but are always
described as perpendicular

I'd have thought 'normal' was the more usual term.
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Dave Page
 
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Default Raising Roof Joists for Loft Flooring

Doctor Drivel wrote:

As he is removing the old insulation, it is best seal up the holes where
cable and pipes penetrate with silicon, then lat a poly vapour barrier
on the plasterboard/joist. Pin it with a staple gun to side of the
joists and tape the joins with big overlaps. Then lay the insulation and
lay the new joists. Then make sure the hatch is sealed and insulated too.


Is that just to stop drafts, or for any other reason? The ceiling
appears to be chipboard rather than plasterboard here.

Dave
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Dave Page
 
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Default Raising Roof Joists for Loft Flooring

wrote:

Lets review the options.


1. Lay new joists on old at 90 degrees This will leave you with a
very weak floor, as well as being a pain to insulate.


Hmm, why would this lead to a weak floor? I figured that laying the new
joists at 90 degrees to the old ones would spread load across the old
joists, and laying the new floorboards across the

This method has the advantage that I can space my new joists at 400mm
(the pre-cut width of the insulation roll) rather than having to deal
with the existing 350mm joist spacing, and means that I can do the loft
in fewer "strips" of insulation (three or four as opposed to a dozen).

Other people have commented that insulation roll is "supposed" to be
laid *across* the joists. I have to assume that this precludes flooring
the loft space, and that if I want to floor my loft space, I'll need to
lay the roll *along* the joists.

3. Add new 4x2 joists to the top of the old ones, inline, attaching
with glue and screws.


Yeah, this was my original plan, and looks like being what I'll end up
doing after all, possibly using the poly vapour barrier mentioned by
Doctor Drivel in
ews.net also.

4. Add new wood on every other joist This will cause damage to the
ceiling, as the differing loads will try to mildly corrugate the
non-flexible plaster ceiling. Expect cracking and damage.


OK, I appreciate now that this is a bad idea.

Dave


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Doctor Drivel
 
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Default Raising Roof Joists for Loft Flooring


"Dave Page" wrote in message
...
wrote:

Lets review the options.


1. Lay new joists on old at 90 degrees This will leave you with a very
weak floor, as well as being a pain to insulate.


Hmm, why would this lead to a weak floor? I figured that laying the new
joists at 90 degrees to the old ones would spread load across the old
joists, and laying the new floorboards across the

This method has the advantage that I can space my new joists at 400mm
(the pre-cut width of the insulation roll) rather than having to deal
with the existing 350mm joist spacing, and means that I can do the loft
in fewer "strips" of insulation (three or four as opposed to a dozen).

Other people have commented that insulation roll is "supposed" to be
laid *across* the joists. I have to assume that this precludes flooring
the loft space, and that if I want to floor my loft space, I'll need to
lay the roll *along* the joists.


Lay insulation between the joists and another layer 90 degrees to that.

I have seen a loft floor raised over 1 foot by using short pieces of 4X2.
all the same length. These were on end on the existing joists vertically,
and secured by small angle pieces. On top on the 4x2s long lengths of 4x2s
were laid and 6" screws driven in. These were secured to the gable end wall
by joist hangers, which also takes weight off the ceiling. The odd cross
brace was inserted so the floor did not wobble, and the chipboard laid on
top being well screwed down. The chipboard tightened up the whole floor.
MDF was used around the loft hatch, which also added rigidity to the floor
too. Easy to do if you have a chop saw and an Impact Driver. This gap was
filled with spray-in Warmcell insulation, which also makes the ceiling
air-tight too. Warmcell has the equiv performance of Rockwool that is 25%
thicker.


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Doctor Drivel
 
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Default Raising Roof Joists for Loft Flooring


"Dave Page" wrote in message
...
Doctor Drivel wrote:

As he is removing the old insulation, it is best seal up the holes where
cable and pipes penetrate with silicon, then lat a poly vapour barrier on
the plasterboard/joist. Pin it with a staple gun to side of the joists
and tape the joins with big overlaps. Then lay the insulation and lay
the new joists. Then make sure the hatch
is sealed and insulated too.


Is that just to stop drafts, or for any other reason? The ceiling appears
to be chipboard rather than plasterboard here.


About 42% of heat loss in UK homes is via air-leakages. Preventing water
vapour from entering the cold loft prevents condensation on the timbers,
hence the sealed loft hatch.


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Dave Page
 
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Default Raising Roof Joists for Loft Flooring

Doctor Drivel wrote:

Other people have commented that insulation roll is "supposed" to
be laid *across* the joists. I have to assume that this precludes
flooring the loft space, and that if I want to floor my loft space,
I'll need to lay the roll *along* the joists.


Lay insulation between the joists and another layer 90 degrees to
that.


I can't do that without laying the new joists at 90 degrees to the old
joists, which I'm told upthread would be a bad idea, or covering the joists.

I have seen a loft floor raised over 1 foot by using short pieces of
4X2. all the same length. These were on end on the existing joists
vertically, and secured by small angle pieces.


Hmm, this sounds like a bigger project in terms of time and complexity
than I can budget for at the moment. Nice idea though.

Dave
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Default Raising Roof Joists for Loft Flooring

Dave Page wrote:
wrote:

Lets review the options.


1. Lay new joists on old at 90 degrees This will leave you with a
very weak floor, as well as being a pain to insulate.


Hmm, why would this lead to a weak floor? I figured that laying the new
joists at 90 degrees to the old ones would spread load across the old
joists, and laying the new floorboards across the


you'd have exactly the same wood supporting as you have now, and 3" is
marginal. Spreading a roomful of load out over a room makes little
difference, it only helps with high point loads, not with total load,
deflection or rigidity.


This method has the advantage that I can space my new joists at 400mm
(the pre-cut width of the insulation roll) rather than having to deal
with the existing 350mm joist spacing, and means that I can do the loft
in fewer "strips" of insulation (three or four as opposed to a dozen).


minor in comparison to leaving yourself with a borderline floor support
structure.


Other people have commented that insulation roll is "supposed" to be
laid *across* the joists. I have to assume that this precludes flooring
the loft space,


thats how its done when theres no flooring. With flooring, the goods
themselves will trap air, if packed in cardboard boxes, and so will
insulate some more. You can roll insulation out on any unused floored
areas if you wish.


3. Add new 4x2 joists to the top of the old ones, inline, attaching
with glue and screws.


Yeah, this was my original plan, and looks like being what I'll end up
doing after all, possibly using the poly vapour barrier mentioned by
Doctor Drivel in


yes


NT

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Doctor Drivel
 
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Default Raising Roof Joists for Loft Flooring


"Dave Page" wrote in message
...
Doctor Drivel wrote:

Other people have commented that insulation roll is "supposed" to be
laid *across* the joists. I have to assume that this precludes flooring
the loft space, and that if I want to floor my loft space,
I'll need to lay the roll *along* the joists.


Lay insulation between the joists and another layer 90 degrees to that.


I can't do that without laying the new joists at 90 degrees to the old
joists, which I'm told upthread would be a bad idea,


It is not. It speads the load and vastly reduces cold bridging.

or covering the joists.

I have seen a loft floor raised over 1 foot by using short pieces of 4X2.
all the same length. These were on end on the existing joists vertically,
and secured by small angle pieces.


Hmm, this sounds like a bigger project in terms of time and complexity
than I can budget for at the moment. Nice idea though.


Not expensive to do. Yet the results are well pleasing in many aspects.


Dave


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