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Default Installing a loft floor

On 21/10/2012 13:09, GMM wrote:
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).


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......


If you can rule out that the space will ever be converted to habitable,
then you can undersize a tad from the tabulated values. As Tony
mentioned above, its normally the deflection limits that dictate the
size rather than the shear or bending limits. (i.e the floor would be
likely to damage decorative finishes, feel to bouncy, and upset
inhabitants of rooms below, long before the timber is in danger of
actually failing)

For your application (i.e. with the new beams some distance above the
existing ceiling, and not ceiling to be mounted on the underside of the
new joists), deflection beyond normal limits is a non issue. So it
reduces to a problem of what is adequate in terms of bending and shear
loading on the timber (assuming you don't mind it feeling a little more
bouncy than "normal" given that you know it is still structurally sound).

Perhaps a play Tony's excellent bit of software might be in order
(assuming there is still a demo version available for download?)



--
Cheers,

John.

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

On Sunday, October 21, 2012 4:25:44 PM UTC+1, John Rumm wrote:
On 21/10/2012 13:09, GMM wrote:

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).




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......




If you can rule out that the space will ever be converted to habitable,

then you can undersize a tad from the tabulated values. As Tony

mentioned above, its normally the deflection limits that dictate the

size rather than the shear or bending limits. (i.e the floor would be

likely to damage decorative finishes, feel to bouncy, and upset

inhabitants of rooms below, long before the timber is in danger of

actually failing)



For your application (i.e. with the new beams some distance above the

existing ceiling, and not ceiling to be mounted on the underside of the

new joists), deflection beyond normal limits is a non issue. So it

reduces to a problem of what is adequate in terms of bending and shear

loading on the timber (assuming you don't mind it feeling a little more

bouncy than "normal" given that you know it is still structurally sound).



Perhaps a play Tony's excellent bit of software might be in order

(assuming there is still a demo version available for download?)







--

Cheers,



John.



/================================================== ===============\

| Internode Ltd - http://www.internode.co.uk |

|-----------------------------------------------------------------|

| John Rumm - john(at)internode(dot)co(dot)uk |

\================================================= ================/


Yes John - it may potentially be that 2 x 6 joists (which are significantly cheaper per metre) could do an
adequate job in this application, if they are available (my local timber yard couldn't supply that length
for the living room when I was costing it: There, the lower spec was due to the wall running along the
middle, effectively halving the span).

TBH, I didn't spot Tony's software - I thought he just mentioned the rule of thumb(!). If I did go below
spec (say 4m of 2 x 6), it would be great to have some idea of how wobbly such a floor would be. The
joist tables just give maximum length for size, as far as I can see.

I'd still feel a little uncomfortable that it would deny the option of making the space habitable in the
future though, even though the rest of the house is big enough that it shouldn't be an issue.
Although I get the point that BR specs change over time, they surely can't ask for joist that are much
deeper than they require now, so I would have thought the current specs won't change much.

(Apologies if my posts are hard to read. Someone told me a while ago they weren't wrapping, whilst in
a recent thread someone else told me they had a lot of empty lines!)
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Default Installing a loft floor

On 21/10/2012 17:47, GMM wrote:
On Sunday, October 21, 2012 4:25:44 PM UTC+1, John Rumm wrote:
On 21/10/2012 13:09, GMM wrote:


If you can rule out that the space will ever be converted to habitable,
then you can undersize a tad from the tabulated values. As Tony

mentioned above, its normally the deflection limits that dictate the
size rather than the shear or bending limits. (i.e the floor would be
likely to damage decorative finishes, feel to bouncy, and upset
inhabitants of rooms below, long before the timber is in danger of
actually failing)

For your application (i.e. with the new beams some distance above the
existing ceiling, and not ceiling to be mounted on the underside of the
new joists), deflection beyond normal limits is a non issue. So it
reduces to a problem of what is adequate in terms of bending and shear
loading on the timber (assuming you don't mind it feeling a little more
bouncy than "normal" given that you know it is still structurally sound).



Perhaps a play Tony's excellent bit of software might be in order
(assuming there is still a demo version available for download?)


Yes John - it may potentially be that 2 x 6 joists (which are significantly cheaper per metre) could do an
adequate job in this application, if they are available (my local timber yard couldn't supply that length
for the living room when I was costing it: There, the lower spec was due to the wall running along the
middle, effectively halving the span).


A timber merchant ought to be able to get 6x2 in 5.3m lengths at least.

TBH, I didn't spot Tony's software - I thought he just mentioned the rule of thumb(!). If I did go below
spec (say 4m of 2 x 6), it would be great to have some idea of how wobbly such a floor would be. The
joist tables just give maximum length for size, as far as I can see.


I just checked, there is still a demo available. It has printing
knobbled - but that won't be a handicap for your needs.

http://www.superbeam.co.uk/sbwdemo.htm

(the usual caveats about it letting you design unsafe structures faster
apply, if you don't stick in sensible values!)

It will show you the calculated deflection for whatever load you apply,
and also tell you when you are exceeding the safe working limits on the
timber.

If you model your longest timber that should let you get a feel for the
changes. The loadings to apply for a normal floor appear further up the
thread (if you know what you are storing etc you may be able to use
lower figures)

I'd still feel a little uncomfortable that it would deny the option of making the space habitable in the
future though, even though the rest of the house is big enough that it shouldn't be an issue.


Might be worth working out what you could "get away with" and then
comparing the cost difference to doing it to full spec.

Although I get the point that BR specs change over time, they surely can't ask for joist that are much
deeper than they require now, so I would have thought the current specs won't change much.


I would not expect them to change in substance at all really. They may
grow to include more on composite joists (i.e. man made beams with
struts top and bottom and some sheet material webbing)

(Apologies if my posts are hard to read. Someone told me a while ago they weren't wrapping, whilst in
a recent thread someone else told me they had a lot of empty lines!)


Its a combination of not wrapping and all the lines being double spaced.
The former is easy to fix in a reply with a quick CTRL + R in
thunderbird. That latter takes slightly more editing!



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
  #44   Report Post  
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Posts: 9,560
Default Installing a loft floor

On Sunday, October 21, 2012 4:07:53 PM UTC+1, John Rumm wrote:
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.


That's exactly the point. All Victorian loft floor joists were compliant for habitable use at time of building, but no BCO is going to accept them in a conversion today.


NT

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.

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GMM GMM is offline
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Default Installing a loft floor

On Sunday, October 21, 2012 7:33:24 PM UTC+1, John Rumm wrote:
On 21/10/2012 17:47, GMM wrote:

On Sunday, October 21, 2012 4:25:44 PM UTC+1, John Rumm wrote:


On 21/10/2012 13:09, GMM wrote:




If you can rule out that the space will ever be converted to habitable,


then you can undersize a tad from the tabulated values. As Tony




mentioned above, its normally the deflection limits that dictate the


size rather than the shear or bending limits. (i.e the floor would be


likely to damage decorative finishes, feel to bouncy, and upset


inhabitants of rooms below, long before the timber is in danger of


actually failing)




For your application (i.e. with the new beams some distance above the


existing ceiling, and not ceiling to be mounted on the underside of the


new joists), deflection beyond normal limits is a non issue. So it


reduces to a problem of what is adequate in terms of bending and shear


loading on the timber (assuming you don't mind it feeling a little more


bouncy than "normal" given that you know it is still structurally sound).








Perhaps a play Tony's excellent bit of software might be in order


(assuming there is still a demo version available for download?)




Yes John - it may potentially be that 2 x 6 joists (which are significantly cheaper per metre) could do an


adequate job in this application, if they are available (my local timber yard couldn't supply that length


for the living room when I was costing it: There, the lower spec was due to the wall running along the


middle, effectively halving the span).




A timber merchant ought to be able to get 6x2 in 5.3m lengths at least.



TBH, I didn't spot Tony's software - I thought he just mentioned the rule of thumb(!). If I did go below


spec (say 4m of 2 x 6), it would be great to have some idea of how wobbly such a floor would be. The


joist tables just give maximum length for size, as far as I can see.




I just checked, there is still a demo available. It has printing

knobbled - but that won't be a handicap for your needs.



http://www.superbeam.co.uk/sbwdemo.htm



(the usual caveats about it letting you design unsafe structures faster

apply, if you don't stick in sensible values!)



It will show you the calculated deflection for whatever load you apply,

and also tell you when you are exceeding the safe working limits on the

timber.



If you model your longest timber that should let you get a feel for the

changes. The loadings to apply for a normal floor appear further up the

thread (if you know what you are storing etc you may be able to use

lower figures)



I'd still feel a little uncomfortable that it would deny the option of making the space habitable in the


future though, even though the rest of the house is big enough that it shouldn't be an issue.




Might be worth working out what you could "get away with" and then

comparing the cost difference to doing it to full spec.



Although I get the point that BR specs change over time, they surely can't ask for joist that are much


deeper than they require now, so I would have thought the current specs won't change much.




I would not expect them to change in substance at all really. They may

grow to include more on composite joists (i.e. man made beams with

struts top and bottom and some sheet material webbing)



(Apologies if my posts are hard to read. Someone told me a while ago they weren't wrapping, whilst in


a recent thread someone else told me they had a lot of empty lines!)




Its a combination of not wrapping and all the lines being double spaced.

The former is easy to fix in a reply with a quick CTRL + R in

thunderbird. That latter takes slightly more editing!







--

Cheers,



John.



/================================================== ===============\

| Internode Ltd - http://www.internode.co.uk |

|-----------------------------------------------------------------|

| John Rumm - john(at)internode(dot)co(dot)uk |

\================================================= ================/


Thanks for the link - Now I have to find a Windows PC I can spark up and run the software - should be interesting.

I suspect a narrower joist could be significantly cheaper for these timbers, although it might not make a substantial impact on the job cost overall.
I've rather taken a 'do it properly and do it once' approach to this house, rather than being cost-driven.

I did toy at one stage with the prospects for making up composite joists in situ, given the access issues, but decided that would just add another variable (and potential disaster) to the equation (!)

Must have another go at Thunderbird for this group. I had it working, then it wouldn't post for some reason.


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Posts: 25,191
Default Installing a loft floor

On 21/10/2012 21:42, wrote:
On Sunday, October 21, 2012 4:07:53 PM UTC+1, John Rumm wrote:
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.


That's exactly the point. All Victorian loft floor joists were
compliant for habitable use at time of building, but no BCO is going
to accept them in a conversion today.


I don't quite follow the line of thought. A loft floor in 1924 was *not*
designed for habitable use then, so its no surprise it would not be
considered adequate now.

Your point seems to be that the definition of "habitable" did not exist
in 1924. However to cut through the confusion, look at what would have
been installed in 1924 for a normal 1st floor set of joists, since that
will have been designed for what we would today call habitable. If the
loft had similar spans but thinner joists, (which which is a safe bet)
then its not habitable - then or now.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd -
http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
  #47   Report Post  
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Posts: 25,191
Default Installing a loft floor

On 22/10/2012 10:19, GMM wrote:

Thanks for the link - Now I have to find a Windows PC I can spark up
and run the software - should be interesting.


Probably not as "industry standard" or trustworthy, but there are a
number of smart phone apps about that will do calcs at least on a single
beam. Might be worth trying one of those if you have platform for that.

I suspect a narrower joist could be significantly cheaper for these
timbers, although it might not make a substantial impact on the job
cost overall. I've rather taken a 'do it properly and do it once'
approach to this house, rather than being cost-driven.


It depends a bit on the layout and how many joist hangers you need etc.
Those will be the same price regardless.

I did toy at one stage with the prospects for making up composite
joists in situ, given the access issues, but decided that would just
add another variable (and potential disaster) to the equation (!)

Must have another go at Thunderbird for this group. I had it
working, then it wouldn't post for some reason.


It ought to be fairly painless for newsgroups if you are using your ISPs
newsserver. If using a third party one, you may need to turn on the
"request authentication" option in the account settings.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Posts: 9,560
Default Installing a loft floor

On Monday, October 22, 2012 2:38:42 PM UTC+1, John Rumm wrote:
On 21/10/2012 21:42, wrote:
On Sunday, October 21, 2012 4:07:53 PM UTC+1, John Rumm wrote:
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.


That's exactly the point. All Victorian loft floor joists were
compliant for habitable use at time of building, but no BCO is going
to accept them in a conversion today.


I don't quite follow the line of thought. A loft floor in 1924 was *not*
designed for habitable use then, so its no surprise it would not be
considered adequate now.
Your point seems to be that the definition of "habitable" did not exist
in 1924. However to cut through the confusion, look at what would have
been installed in 1924 for a normal 1st floor set of joists, since that
will have been designed for what we would today call habitable. If the
loft had similar spans but thinner joists, (which which is a safe bet)
then its not habitable - then or now.


I don't think you've followed what I'm saying at all.


NT
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Default Installing a loft floor

On 22/10/2012 14:43, John Rumm wrote:
On 22/10/2012 10:19, GMM wrote:

Thanks for the link - Now I have to find a Windows PC I can spark up
and run the software - should be interesting.


Probably not as "industry standard" or trustworthy, but there are a
number of smart phone apps about that will do calcs at least on a single
beam. Might be worth trying one of those if you have platform for that.

I suspect a narrower joist could be significantly cheaper for these
timbers, although it might not make a substantial impact on the job
cost overall. I've rather taken a 'do it properly and do it once'
approach to this house, rather than being cost-driven.


It depends a bit on the layout and how many joist hangers you need etc.
Those will be the same price regardless.

I did toy at one stage with the prospects for making up composite
joists in situ, given the access issues, but decided that would just
add another variable (and potential disaster) to the equation (!)

Must have another go at Thunderbird for this group. I had it
working, then it wouldn't post for some reason.


It ought to be fairly painless for newsgroups if you are using your ISPs
newsserver. If using a third party one, you may need to turn on the
"request authentication" option in the account settings.


I should take a browse through the phone apps (without wishing to turn
the thread into another debate about which phone is best!)
Your comments about ISP newservers made me realise that I set
Thunderbird up for home, then might have failed to post over a different
WiFi connection, so if this posts, problem solved (ish)
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On 22/10/2012 20:28, wrote:
On Monday, October 22, 2012 2:38:42 PM UTC+1, John Rumm wrote:
On 21/10/2012 21:42,
wrote:
On Sunday, October 21, 2012 4:07:53 PM UTC+1, John Rumm wrote:
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.


That's exactly the point. All Victorian loft floor joists were
compliant for habitable use at time of building, but no BCO is going
to accept them in a conversion today.


I don't quite follow the line of thought. A loft floor in 1924 was *not*
designed for habitable use then, so its no surprise it would not be
considered adequate now.
Your point seems to be that the definition of "habitable" did not exist
in 1924. However to cut through the confusion, look at what would have
been installed in 1924 for a normal 1st floor set of joists, since that
will have been designed for what we would today call habitable. If the
loft had similar spans but thinner joists, (which which is a safe bet)
then its not habitable - then or now.


I don't think you've followed what I'm saying at all.


So what is your point then? I thought we had covered:

1) Standards have edged up?
Agreed. But not hugely.

2) Skimpy joists in a loft were acceptable as a habitable room floor in
the past?
Nope, don't buy it for a moment. They were acceptable as a loft floor
and that is all - but there was no anticipation that was going to be
used as a bedroom of office etc. They were also to a much lower standard
than was deemed necessary for all the other "proper" floors in the same
building.

3) Joists will survive loadings far beyond those specified in the
building regs?
Yup agreed. The specs are primarily intended to limit deflection, and
excessive deflection occurs long before structural failure.

4) You can still use skimpy timbers if they are short enough?
Yup agreed, nothing much has changed there.

5) Joist sizes are specced on sound transmission?
I don't believe that really comes into it. Specs on sound transmission
have got much stronger in recent times, but joist sizes themselves have
not increased as a result. Joist support techniques have changed -
reducing wall penetrations, ensuring adequate insulating material is
included in floor construction to reduce noise. Eliminating gaps and air
paths are all partly related to reducing noise transmission as well as
improving thermal performance. Fire protection rules have also
tightened, and that has had a knock on on ceiling coverings (i.e. 1/2"
PB and skim, not 9mm etc, intumescent covers over ceiling penetrations).

Have I missed any?


--
Cheers,

John.

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On 22/10/2012 21:48, GMM wrote:
On 22/10/2012 14:43, John Rumm wrote:
On 22/10/2012 10:19, GMM wrote:

Thanks for the link - Now I have to find a Windows PC I can spark up
and run the software - should be interesting.


Probably not as "industry standard" or trustworthy, but there are a
number of smart phone apps about that will do calcs at least on a single
beam. Might be worth trying one of those if you have platform for that.

I suspect a narrower joist could be significantly cheaper for these
timbers, although it might not make a substantial impact on the job
cost overall. I've rather taken a 'do it properly and do it once'
approach to this house, rather than being cost-driven.


It depends a bit on the layout and how many joist hangers you need etc.
Those will be the same price regardless.

I did toy at one stage with the prospects for making up composite
joists in situ, given the access issues, but decided that would just
add another variable (and potential disaster) to the equation (!)

Must have another go at Thunderbird for this group. I had it
working, then it wouldn't post for some reason.


It ought to be fairly painless for newsgroups if you are using your ISPs
newsserver. If using a third party one, you may need to turn on the
"request authentication" option in the account settings.


I should take a browse through the phone apps (without wishing to turn
the thread into another debate about which phone is best!)


Hence why I did not mention a platform. I have seen them for mine, so I
presume they exist for the others... I wonder if Tony is planning on an
Android or iOS port of superbeam proper?

Your comments about ISP newservers made me realise that I set
Thunderbird up for home, then might have failed to post over a different
WiFi connection, so if this posts, problem solved (ish)


Normally if the newsserver accepts authentication then it will allow
posts from any network. If it does not, then it will usually only accept
them from its "own" network address block.

BTW the quoting looks much better - no double spaced lines anymore ;-)


--
Cheers,

John.

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\================================================= ================/
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On Tue, 23 Oct 2012 01:43:39 +0100 John Rumm wrote :
Hence why I did not mention a platform. I have seen them for mine, so I
presume they exist for the others... I wonder if Tony is planning on an
Android or iOS port of superbeam proper?


No current plans. Would it be an interesting project? Probably. Would it
make any money, given what people are used to paying for mobile apps?
Probably not. If I was looking for an alternative platform, then the most
likely route would be a web-based app, accessible via any browser.

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

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I should take a browse through the phone apps (without wishing to turn
the thread into another debate about which phone is best!)


Hence why I did not mention a platform. I have seen them for mine, so I
presume they exist for the others... I wonder if Tony is planning on an
Android or iOS port of superbeam proper?

Your comments about ISP newservers made me realise that I set
Thunderbird up for home, then might have failed to post over a different
WiFi connection, so if this posts, problem solved (ish)


Normally if the newsserver accepts authentication then it will allow
posts from any network. If it does not, then it will usually only accept
them from its "own" network address block.

BTW the quoting looks much better - no double spaced lines anymore ;-)


Excellent! Problem solved then (now to work on the typos....)
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On 23/10/2012 01:43, John Rumm wrote:


Probably not as "industry standard" or trustworthy, but there

are a number of smart phone apps about that will do calcs at least on a
single beam.
Might be worth trying one of those if you have platform for that.


It's interesting that there seem to be more apps available than
web-based calculators. Unfortunately most of these seem to be in
American and I'm not sure how C16 compares with their specs but, putting
a trial dimension of 4m in, using Redwood or Southern Pine (which seem
to come out the same and probably equate broadly) gives a deflection of
69mm for a 6x2 for a light floor loading, which seems an awful lot. For
some reason, the one I was using seems not to accept 2" beams after the
first use so I can't go back and check but the deflection for 8x2 was
about 20-something mm so about a 2" difference.
So to keep the floor clear of the ceiling, either size would have to be
mounted at the same height (roughly), which is interesting. So it might
well be best to go for the bigger size and do it 'properly' after all.
I suspect this is a worst case as adding boards and struts would stiffen
the whole thing. On the other hand, there is bound to be a bit of
gradual sag over time, as you saw, even in an unloaded joist, which
might offset this.
I suppose an alternative (to use narrower timbers) would be to change
the joist pattern but the only way I can see to do this would be to put
something very substantial across the middle of the 6m dimension (or
split it into 3) and run the joists at right angles to this. This would
make most joists around 3m, where 6x2 would probably be fine. I'm not
sure this would be wise though as it would increase the loading on the
walls to a great extent where this beam was mounted and would generate
problems with actually getting everything into place.
Thinking back to my last place, it's certainly true that we had a loft
which I floored using chipboard panels onto 4x2 ceiling joists with no
problems. I think the differences there were a) the spans were much
smaller and b) I didn't give it any thought at all!


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On 24/10/2012 09:55, GMM wrote:
On 23/10/2012 01:43, John Rumm wrote:


Probably not as "industry standard" or trustworthy, but there

are a number of smart phone apps about that will do calcs at least on a
single beam.
Might be worth trying one of those if you have platform for that.


It's interesting that there seem to be more apps available than
web-based calculators. Unfortunately most of these seem to be in
American and I'm not sure how C16 compares with their specs but, putting
a trial dimension of 4m in, using Redwood or Southern Pine (which seem
to come out the same and probably equate broadly) gives a deflection of
69mm for a 6x2 for a light floor loading, which seems an awful lot. For
some reason, the one I was using seems not to accept 2" beams after the
first use so I can't go back and check but the deflection for 8x2 was
about 20-something mm so about a 2" difference.


Give me the specs of a beam if you like and I will see what numbers I get...

So to keep the floor clear of the ceiling, either size would have to be
mounted at the same height (roughly), which is interesting. So it might
well be best to go for the bigger size and do it 'properly' after all.
I suspect this is a worst case as adding boards and struts would stiffen
the whole thing. On the other hand, there is bound to be a bit of
gradual sag over time, as you saw, even in an unloaded joist, which
might offset this.


When you add floor boards, you can use load sharing in the calcs - since
you tie a number of them together in effect, the statistical variation
is likely to reduce, so you can assume stiffness's no so close to worst
case.

I suppose an alternative (to use narrower timbers) would be to change
the joist pattern but the only way I can see to do this would be to put
something very substantial across the middle of the 6m dimension (or
split it into 3) and run the joists at right angles to this. This would
make most joists around 3m, where 6x2 would probably be fine. I'm not
sure this would be wise though as it would increase the loading on the
walls to a great extent where this beam was mounted and would generate
problems with actually getting everything into place.
Thinking back to my last place, it's certainly true that we had a loft
which I floored using chipboard panels onto 4x2 ceiling joists with no
problems. I think the differences there were a) the spans were much
smaller and b) I didn't give it any thought at all!


Well indeed. Also a loft just used for storage will not be loaded to
anything close to what one needs to allow for a room.


--
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John.

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On Thu, 18 Oct 2012 16:07:49 -0700 (PDT), 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:


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.


In my Victorian house I put a 4 foot fluorescent light up in my study (an ex-bedroom) and
was puzzled by why the second screw wouldn't reach through the L&P ceiling to the joist.
On standing back from light I realised the reason was that the ceiling had sagged and my
fluorescent was bridging an inverted hump. It's now fixed with longer screws and with the
centre touching the ceiling the ends are a good inch below the ceiling - so a deflection
of about 1"/2'.

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

I have to build a floor in a loft.
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 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?


I'd put at a beam at right angles to the joists in the middle of the ceiling, supported by acro-props. This will halve the effective length of the joists, and make them plenty man enough for the job.

You'll then need boards on top of the joists to stand on.

Lastly, to get decent access into the loft space I need to create a
new doorway. The only way I can approach this is from the inside
of the loft. 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?


Sounds like a reasonable plan. I'd probably just use a rawl-plug
and No 10/ No 12 screw. It doesn't have to take much weight, and it
doesn't have to take it for long.
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On 24/10/2012 16:55, John Rumm wrote:
On 24/10/2012 09:55, GMM wrote:
On 23/10/2012 01:43, John Rumm wrote:


Probably not as "industry standard" or trustworthy, but there

are a number of smart phone apps about that will do calcs at least on a
single beam.
Might be worth trying one of those if you have platform for that.


It's interesting that there seem to be more apps available than
web-based calculators. Unfortunately most of these seem to be in
American and I'm not sure how C16 compares with their specs but, putting
a trial dimension of 4m in, using Redwood or Southern Pine (which seem
to come out the same and probably equate broadly) gives a deflection of
69mm for a 6x2 for a light floor loading, which seems an awful lot. For
some reason, the one I was using seems not to accept 2" beams after the
first use so I can't go back and check but the deflection for 8x2 was
about 20-something mm so about a 2" difference.


Give me the specs of a beam if you like and I will see what numbers I
get...


Thanks John, that would be very useful. All lengths are 4m (a little
variation but no more than 100mm) and the TRADA tables say a 47 x 195
joist is good for that at 400 centres but of course give no further
information. (A number of apps etc simply give the same data in their
calculators - you put in the size and it tells you the max span.)

Clearly very small ones would be inadequate at this length, but it would
be interesting to know what the performance of 7" (ie 47 x 170) and 6"
(47 x 145) would be at 4m for C16 timber. From what the tables
indicate, the advantage of C24 is pretty minimal, so hardly worth the
trouble of sourcing etc except in very marginal situations).

I'll most likely cover with chipboard (8x2 t/g sheets), which comes in
18 or 22mm. I'm assuming that there's little difference here for 400mm
joist centres (and would go for 18 as it's lighter) and the more
important factor is to screw it down to every joist but I could easily
be corrected on this (!)

It's also pretty clear that a span of 4m will benefit from strutting at
mid span, so that's on the agenda too.

Friday night - must be time for a cold one (!)

Cheers!

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On 26/10/2012 23:45, John Rumm wrote:
On 26/10/2012 19:11, GMM wrote:
On 24/10/2012 16:55, John Rumm wrote:
On 24/10/2012 09:55, GMM wrote:
On 23/10/2012 01:43, John Rumm wrote:


Probably not as "industry standard" or trustworthy, but there
are a number of smart phone apps about that will do calcs at least on a
single beam.
Might be worth trying one of those if you have platform for that.


It's interesting that there seem to be more apps available than
web-based calculators. Unfortunately most of these seem to be in
American and I'm not sure how C16 compares with their specs but,
putting
a trial dimension of 4m in, using Redwood or Southern Pine (which seem
to come out the same and probably equate broadly) gives a deflection of
69mm for a 6x2 for a light floor loading, which seems an awful lot.
For
some reason, the one I was using seems not to accept 2" beams after the
first use so I can't go back and check but the deflection for 8x2 was
about 20-something mm so about a 2" difference.

Give me the specs of a beam if you like and I will see what numbers I
get...


Thanks John, that would be very useful. All lengths are 4m (a little
variation but no more than 100mm) and the TRADA tables say a 47 x 195
joist is good for that at 400 centres but of course give no further
information. (A number of apps etc simply give the same data in their
calculators - you put in the size and it tells you the max span.)


Well if I model that with a uniformly distributed load of 0.8kN/m (long
term load), and treat them as a load sharing system, you get a
deflection of just under 11mm. Go down to 175mm and the deflection goes
up to just under 15mm. However its worth noting that it is also flagged
as failing in maximum permitted bending stress at that point. 150mm and
deflection is nearly 23mm. 100mm and deflection is approaching 80mm!

That is a full floor load though - unless storing a large magazine or
record collection its unlikely you would reach that.

Clearly very small ones would be inadequate at this length, but it would
be interesting to know what the performance of 7" (ie 47 x 170) and 6"
(47 x 145) would be at 4m for C16 timber. From what the tables
indicate, the advantage of C24 is pretty minimal, so hardly worth the
trouble of sourcing etc except in very marginal situations).


C24 at 175 for example would be a "pass" on 175mm (deflection 7.61mm)
and on 150mm (11.98). (125mm and you are back to failing in bending stress)

Note also you can push it firther with short term loads - so you don't
necessarily need to make adjustments to factor in someone clod hoppering
around up there shifting the boxes.

I'll most likely cover with chipboard (8x2 t/g sheets), which comes in
18 or 22mm. I'm assuming that there's little difference here for 400mm
joist centres (and would go for 18 as it's lighter) and the more
important factor is to screw it down to every joist but I could easily
be corrected on this (!)


It interlocks, so only really needs enough screwing in this application
to stop it sliding about.

It's also pretty clear that a span of 4m will benefit from strutting at
mid span, so that's on the agenda too.


It will make it bounce less. How much that matters for storage space is
debatable.

Friday night - must be time for a cold one (!)


Sounds like a good plan ;-)

Thanks for doing that John, it's very interesting: It looks like 150 at
C24 is pretty much comparable to 195 at C16 in terms of deflection: I
didn't think the difference between the two would be anywhere near as
much, from the other information I've seen.
Of course, the C24 may be more expensive even in the smaller size (I'll
have to get a quote) but if it's not too much more, the extra 2" might
be a useful space saving: It would certainly reduce the step up onto
this floor from the new access door, which might make it more user friendly.

(It took me a while to get back - I've been away for a few days and it
seems Firefox can't connect to the server from other networks)

All the best
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On 30/10/2012 12:45, GMM wrote:
On 26/10/2012 23:45, John Rumm wrote:
On 26/10/2012 19:11, GMM wrote:
On 24/10/2012 16:55, John Rumm wrote:
On 24/10/2012 09:55, GMM wrote:
On 23/10/2012 01:43, John Rumm wrote:


Probably not as "industry standard" or trustworthy, but there
are a number of smart phone apps about that will do calcs at least
on a
single beam.
Might be worth trying one of those if you have platform for that.


It's interesting that there seem to be more apps available than
web-based calculators. Unfortunately most of these seem to be in
American and I'm not sure how C16 compares with their specs but,
putting
a trial dimension of 4m in, using Redwood or Southern Pine (which seem
to come out the same and probably equate broadly) gives a
deflection of
69mm for a 6x2 for a light floor loading, which seems an awful lot.
For
some reason, the one I was using seems not to accept 2" beams after
the
first use so I can't go back and check but the deflection for 8x2 was
about 20-something mm so about a 2" difference.

Give me the specs of a beam if you like and I will see what numbers I
get...


Thanks John, that would be very useful. All lengths are 4m (a little
variation but no more than 100mm) and the TRADA tables say a 47 x 195
joist is good for that at 400 centres but of course give no further
information. (A number of apps etc simply give the same data in their
calculators - you put in the size and it tells you the max span.)


Well if I model that with a uniformly distributed load of 0.8kN/m (long
term load), and treat them as a load sharing system, you get a
deflection of just under 11mm. Go down to 175mm and the deflection goes
up to just under 15mm. However its worth noting that it is also flagged
as failing in maximum permitted bending stress at that point. 150mm and
deflection is nearly 23mm. 100mm and deflection is approaching 80mm!

That is a full floor load though - unless storing a large magazine or
record collection its unlikely you would reach that.

Clearly very small ones would be inadequate at this length, but it would
be interesting to know what the performance of 7" (ie 47 x 170) and 6"
(47 x 145) would be at 4m for C16 timber. From what the tables
indicate, the advantage of C24 is pretty minimal, so hardly worth the
trouble of sourcing etc except in very marginal situations).


C24 at 175 for example would be a "pass" on 175mm (deflection 7.61mm)
and on 150mm (11.98). (125mm and you are back to failing in bending
stress)

Note also you can push it firther with short term loads - so you don't
necessarily need to make adjustments to factor in someone clod hoppering
around up there shifting the boxes.

I'll most likely cover with chipboard (8x2 t/g sheets), which comes in
18 or 22mm. I'm assuming that there's little difference here for 400mm
joist centres (and would go for 18 as it's lighter) and the more
important factor is to screw it down to every joist but I could easily
be corrected on this (!)


It interlocks, so only really needs enough screwing in this application
to stop it sliding about.

It's also pretty clear that a span of 4m will benefit from strutting at
mid span, so that's on the agenda too.


It will make it bounce less. How much that matters for storage space is
debatable.

Friday night - must be time for a cold one (!)


Sounds like a good plan ;-)

Thanks for doing that John, it's very interesting: It looks like 150 at
C24 is pretty much comparable to 195 at C16 in terms of deflection: I
didn't think the difference between the two would be anywhere near as
much, from the other information I've seen.
Of course, the C24 may be more expensive even in the smaller size (I'll
have to get a quote) but if it's not too much more, the extra 2" might
be a useful space saving: It would certainly reduce the step up onto
this floor from the new access door, which might make it more user
friendly.


I remember when I did my loft conversion that there was some C24
specified (most was C16). It took the timber merchant about an extra
week to order that in for me. Hence it may not be as readily stocked.

(It took me a while to get back - I've been away for a few days and it
seems Firefox can't connect to the server from other networks)


Thunderbird perhaps?

If your mail server supports authentication then you may be able to use
it by turning on the "Always request authentication when connecting to
this server" checkbox in the news server server settings dialogue.


--
Cheers,

John.

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