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Home > Archive > Building and Construction > May 2007 > Finishing garage with truss roof system
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Finishing garage with truss roof system
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| Hello!
I recently purchased a house in Upstate, NY with a 2x4 roof truss
system in a detached garage. The interior dimensions of the garage
are roughly 24' x 24', and the trusses are constructed using plates to
connect the 2x4s. There is no bottom center support -- it looks like
two 12' 2x4s are connected at the middle via a plate on each truss.
Finally, the trusses are spaced 24" on center.
The garage has been in place for around 15 years, so it's plenty
sturdy. I've begun finishing the garage, but I just gave some thought
to whether the truss system will be able to handle the additional
weight of insulation and sheetrock that will be used? The attic space
won't be used for anything other than light storage. Any information
or suggestions would be greatly appreciated. Thanks!
--Jim.
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| HerHusband 2007-05-14, 5:25 pm |
| > I recently purchased a house in Upstate, NY with a 2x4 roof truss
> system in a detached garage. The interior dimensions of the garage
> are roughly 24' x 24', and the trusses are constructed using plates to
> connect the 2x4s. There is no bottom center support -- it looks like
> two 12' 2x4s are connected at the middle via a plate on each truss.
> Finally, the trusses are spaced 24" on center.
> I just gave some thought to whether the truss system will be able
> to handle the additional weight of insulation and sheetrock that
> will be used?
There's no way to know for certain without the specs from the company that
made the truss. I had to include the truss specifications with my building
permit, so you might be able to get that info from your local building
department if you do not have a copy of the plans (for a research fee, I'm
sure). The truss may also be stamped with the company name, in which case
they might have records of that truss.
In any case, every roof truss I have seen has always been designed for at
least 10 pounds dead load on the bottom chord of the truss. A 4x8 sheet of
5/8" sheetrock probably weighs less than 80 pounds. That should work out to
about 2.5 pounds per square foot. With insulation I'm guessing you'd still
be under 3 psf (insulation is rather light). That still leaves plenty of
capacity for light fixtures, garage door tracks and openers, etc.
> The attic space won't be used for anything other than light storage.
Personally, I wouldn't store anything on the bottom chord of a truss unless
the truss was specifically designed to carry that load. But that's me.
You would probably be fine putting christmas decorations, spare pvc pipe,
or fishing poles up there. But, don't try storing your collection of old
magazines, books, that old boat motor, cans of paint, or other heavy
objects. It probably wouldn't be a problem 999 times out of 1000, but it
only takes that 1 time for things to fail. 
Anthony
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| Bob Morrison 2007-05-14, 5:25 pm |
| In a previous post HerHusband wrote...
>
>
> There's no way to know for certain without the specs from the company that
> made the truss. I had to include the truss specifications with my building
> permit, so you might be able to get that info from your local building
> department if you do not have a copy of the plans (for a research fee, I'm
> sure). The truss may also be stamped with the company name, in which case
> they might have records of that truss.
>
> In any case, every roof truss I have seen has always been designed for at
> least 10 pounds dead load on the bottom chord of the truss. A 4x8 sheet of
> 5/8" sheetrock probably weighs less than 80 pounds. That should work out to
> about 2.5 pounds per square foot. With insulation I'm guessing you'd still
> be under 3 psf (insulation is rather light). That still leaves plenty of
> capacity for light fixtures, garage door tracks and openers, etc.
>
>
> Personally, I wouldn't store anything on the bottom chord of a truss unless
> the truss was specifically designed to carry that load. But that's me.
>
Anthony has given a most excellent answer!
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com
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| "Jim" <jimfeck@gmail.com> wrote in message
news:1179157685.196559.125140@w5g2000hsg.googlegroups.com...
> Hello!
>
> I recently purchased a house in Upstate, NY with a 2x4 roof truss
> system in a detached garage. The interior dimensions of the garage
> are roughly 24' x 24', and the trusses are constructed using plates to
> connect the 2x4s. There is no bottom center support -- it looks like
> two 12' 2x4s are connected at the middle via a plate on each truss.
> Finally, the trusses are spaced 24" on center.
>
> The garage has been in place for around 15 years, so it's plenty
> sturdy. I've begun finishing the garage, but I just gave some thought
> to whether the truss system will be able to handle the additional
> weight of insulation and sheetrock that will be used? The attic space
> won't be used for anything other than light storage. Any information
> or suggestions would be greatly appreciated. Thanks!
>
> --Jim.
>
The builder failed to showup the day they dropped off the trusses for my
house in building progress. I happened to be at the building site, told the
guy where to drop off the trusses. The paperwork the driver provided
included the layout of each truss type (hip roof) and so forth, and dwgs of
each. On the last page was a disclaimer regarding using the resulting attic
space for storage.
Dave
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| Thanks to all for the replies! I'll try to find out the truss specs
from the bldg. dept. Out of curiosity (and not wanting to get killed)
-- if there *is* a problem with the trusses, will there generally be
some sign before there's a "real" problem. In other words, will I see
a crack in the ceiling before there's a catastrophic failure and the
roof falls down on my head?
Many thanks again,
--Jim.
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| Bob Morrison 2007-05-21, 5:25 pm |
| In a previous post Jim wrote...
> Thanks to all for the replies! I'll try to find out the truss specs
> from the bldg. dept. Out of curiosity (and not wanting to get killed)
> -- if there *is* a problem with the trusses, will there generally be
> some sign before there's a "real" problem. In other words, will I see
> a crack in the ceiling before there's a catastrophic failure and the
> roof falls down on my head?
>
Generally, the collapse mechanism is failure of the press plate into the
wood. This is a catastrophic failure and can occur without warning.
Failure of one truss can cause a "zipper" effect, also known as a
progressive collapse.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com
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| On May 21, 5:59 pm, Bob Morrison <SpamFigh...@junk.com> wrote:
> Generally, the collapse mechanism is failure of the press plate into the
> wood. This is a catastrophic failure and can occur without warning.
> Failure of onetrusscan cause a "zipper" effect, also known as a
> progressive collapse.
Hmm...okay, thanks Bob. I think... Here's another question: Assuming
that I've got nothing stored up there that wasn't up there before
(aside from the sheetrock and insulation), and given the fact that the
structure has been in place for over 15 years, is it fairly safe to
assume that it'll be okay? In other words, is history a good
indicator, or are trusses like stocks: past performance does not
guarantee future performance?
Also, if I wanted to have someone take a look at the situation, who
would that be? A structural engineer?
Many thanks again.
--Jim.
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| Bob Morrison 2007-05-22, 9:25 am |
| In a previous post Jim wrote...
> Hmm...okay, thanks Bob. I think... Here's another question: Assuming
> that I've got nothing stored up there that wasn't up there before
> (aside from the sheetrock and insulation), and given the fact that the
> structure has been in place for over 15 years, is it fairly safe to
> assume that it'll be okay? In other words, is history a good
> indicator, or are trusses like stocks: past performance does not
> guarantee future performance?
Let's say that the fact that the trusses have been in place for 15 years
with sheetrock and insulation in place and they have not failed is a good
thing. However, it may also be that the roof has never been fully loaded
to capacity by snow load or roof live load, both of which cause tension in
the bottom chord.
> Also, if I wanted to have someone take a look at the situation, who
> would that be? A structural engineer?
>
It will be a lot easier if you can find the original design from the truss
manufacturer. Evaluating an existing press plate truss can be time
consuming and expense. I've done it - once. It is not the truss members
that are the issue, but the press plates. These are optimized by the
truss manufacturer's design program.
One option might be to have the trusses completely redesigned with all
connection loads taken up by plywood gussets. This will not be
inexpensive, not will it be easy to implement any changes.
I just now went back and read your original post. It seems the question
has more to do with using the trusses for attic storage than supporting
sheetrock and insulation. Most modern roof trusses that I have seen are
designed for a superimposed load of about 10 psf on the bottom chord.
This is enough to take care of sheetrock, insulation, lights, etc. but not
much else. So, bottom line. Don't use them for storage of any kind.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com
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| On May 22, 10:16 am, Bob Morrison <SpamFigh...@junk.com> wrote:
> I just now went back and read your original post. It seems the question
> has more to do with using the trusses for attic storage than supporting
> sheetrock and insulation. Most modern roof trusses that I have seen are
> designed for a superimposed load of about 10 psf on the bottom chord.
> This is enough to take care of sheetrock, insulation, lights, etc. but not
> much else. So, bottom line. Don't use them for storage of any kind.
Yeah, that's definitely part of it -- some storage up there would be
nice, but it's not necessary. My biggest concern is getting
flattened. If I post a photo or two of the press plates, would that
tell you anything?
FWIW, I found out that the truss manufacturer is Stock Building
Supply. The previous owner didn't have any other info, and a call to
them turned up that they don't keep records that long.
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| Bob Morrison 2007-05-22, 9:25 pm |
| In a previous post Jim wrote...
> Yeah, that's definitely part of it -- some storage up there would be
> nice, but it's not necessary. My biggest concern is getting
> flattened. If I post a photo or two of the press plates, would that
> tell you anything?
>
A photo wouldn't tell much. Is there some reason you are concerned about
these trusses if you aren't going to store anything in the attic? Are
they showing signs of distress in some way?
Again, from your original post I assume the trusses were designed for a
pretty heavy snow load in upstate New York. The weight of a layer of
sheetrock (even 5/8") and some insulation is most likely only a small
portion of the truss design load.
For your own piece of mind you could ask an engineer (structural or civil
with structural emphasis) for a brief inspection. If it were me I would
probably want to look at 50% or so of the press plate connections just to
be safe. If they look okay then I think you could proceed safely.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com
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"Bob Morrison" <SpamFighter@junk.com> wrote in message
news:MPG.20bd438731ab1f5b989df8@news.west.earthlink.net...
> In a previous post Jim wrote...
>
> A photo wouldn't tell much. Is there some reason you are concerned about
> these trusses if you aren't going to store anything in the attic? Are
> they showing signs of distress in some way?
>
> Again, from your original post I assume the trusses were designed for a
> pretty heavy snow load in upstate New York. The weight of a layer of
> sheetrock (even 5/8") and some insulation is most likely only a small
> portion of the truss design load.
>
> For your own piece of mind you could ask an engineer (structural or civil
> with structural emphasis) for a brief inspection. If it were me I would
> probably want to look at 50% or so of the press plate connections just to
> be safe. If they look okay then I think you could proceed safely.
>
> --
> Bob Morrison, PE, SE
> R L Morrison Engineering Co
> Structural & Civil Engineering
> Poulsbo WA
> bob at rlmorrisonengr dot com
Guys. Please remember that if the bottom chord was designed for 10 psf and
you store heavy material/books/paper etc that runs around 100 psf, 10 times
the design load you might be in trouble not just failure of the plates but
also the bottom chord. Not to mention deflection.
As Bob says do get an local engineer to do some inspection. For a little
expense a good engineer could analyze the truss for load capacity and have
some ideas for your storage, such as half of the space where additional
structure could be added specific to storage.
Just a thought.
CID...
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