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roof thrust problem jbusboom 08-22-2006
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Posted by on August 22, 2006, 5:15 pm
I am building a 20 foot wide barn with a gambrel roof. The trusses are
specially engineered so that no chords are needed (almost like a
scissor truss). This allows me to use the top of the barn as a loft.
But, I want to raise the height of the walls on which the trusses are
supported by 18 to 24 inches so that I have extra head room on the loft
level of the barn. Normally, the floor joists would stop the wall
spreading caused by the thrust of the roof, but since I am raising the
wall height, that is not the case anymore. Will I have a problem if I
don't add any more supports elsewhere (I am not about to use flying
buttresses on my barn). One potential solution I have is to use some
cross bracing from the top of the wall down inward to the floor joists
at an angle every so often along the wall, like:

/
/
/
|\
| \
|----\---------
|

That way I get the extra head room, and the braces won't be in the way.
Any thoughts?


Posted by Glenn on August 22, 2006, 6:25 pm
Personally I would do it just like your little illustration. I
would nail the brace onto the rafter itself and down to the
joist.. Only 20' wide is not much more than a small shed and the
loads have to be small. I'm sure someone will come up with a more
complicated way though.

>I am building a 20 foot wide barn with a gambrel roof.
> The trusses are specially engineered so that no chords
> are needed (almost like a scissor truss). This allows me
> to use the top of the barn as a loft. But, I want to
> raise the height of the walls on which the trusses are
> supported by 18 to 24 inches so that I have extra head
> room on the loft level of the barn. Normally, the floor
> joists would stop the wall spreading caused by the thrust
> of the roof, but since I am raising the wall height, that
> is not the case anymore. Will I have a problem if I
> don't add any more supports elsewhere (I am not about to
> use flying buttresses on my barn). One potential
> solution I have is to use some cross bracing from the top
> of the wall down inward to the floor joists at an angle
> every so often along the wall, like:
>
> /
> /
> /
> |\
> | \
> |----\---------
> |
>
> That way I get the extra head room, and the braces won't
> be in the way. Any thoughts?


Posted by bitternut on August 22, 2006, 7:09 pm
We had a large two story barn that was constructed exactly as your
illustration. It was built about 1900 and is still standing very nicely. We
used to load up the second story with a lot of stuff that seemed to do no
harm.
> Personally I would do it just like your little illustration. I would nail
> the brace onto the rafter itself and down to the joist.. Only 20' wide is
> not much more than a small shed and the loads have to be small. I'm sure
> someone will come up with a more complicated way though.
>
>>I am building a 20 foot wide barn with a gambrel roof.
>> The trusses are specially engineered so that no chords
>> are needed (almost like a scissor truss). This allows me
>> to use the top of the barn as a loft. But, I want to
>> raise the height of the walls on which the trusses are
>> supported by 18 to 24 inches so that I have extra head
>> room on the loft level of the barn. Normally, the floor
>> joists would stop the wall spreading caused by the thrust
>> of the roof, but since I am raising the wall height, that
>> is not the case anymore. Will I have a problem if I
>> don't add any more supports elsewhere (I am not about to
>> use flying buttresses on my barn). One potential
>> solution I have is to use some cross bracing from the top
>> of the wall down inward to the floor joists at an angle
>> every so often along the wall, like:
>>
>> /
>> /
>> /
>> |\
>> | \
>> |----\---------
>> |
>>
>> That way I get the extra head room, and the braces won't
>> be in the way. Any thoughts?
>



Posted by on August 23, 2006, 9:04 am
I am encouraged that a barn build this way over a hundred years ago is
still standing. Do you remember how often along the wall that the
braces were placed? Was it from every rafter (or truss) or more
separated. I would think doing it from every rafter would be a bit
overkill.


bitternut wrote:
> We had a large two story barn that was constructed exactly as your
> illustration. It was built about 1900 and is still standing very nicely. We
> used to load up the second story with a lot of stuff that seemed to do no
> harm.
> > Personally I would do it just like your little illustration. I would nail
> > the brace onto the rafter itself and down to the joist.. Only 20' wide is
> > not much more than a small shed and the loads have to be small. I'm sure
> > someone will come up with a more complicated way though.
> >
> >>I am building a 20 foot wide barn with a gambrel roof.
> >> The trusses are specially engineered so that no chords
> >> are needed (almost like a scissor truss). This allows me
> >> to use the top of the barn as a loft. But, I want to
> >> raise the height of the walls on which the trusses are
> >> supported by 18 to 24 inches so that I have extra head
> >> room on the loft level of the barn. Normally, the floor
> >> joists would stop the wall spreading caused by the thrust
> >> of the roof, but since I am raising the wall height, that
> >> is not the case anymore. Will I have a problem if I
> >> don't add any more supports elsewhere (I am not about to
> >> use flying buttresses on my barn). One potential
> >> solution I have is to use some cross bracing from the top
> >> of the wall down inward to the floor joists at an angle
> >> every so often along the wall, like:
> >>
> >> /
> >> /
> >> /
> >> |\
> >> | \
> >> |----\---------
> >> |
> >>
> >> That way I get the extra head room, and the braces won't
> >> be in the way. Any thoughts?
> >


Posted by Darryl Bailie on August 23, 2006, 11:14 am
When we specify raised tie trusses we specify that they sit on glide shoes.
These let the trusses spread without inducing lateral loads on the top of
the wall.


>I am building a 20 foot wide barn with a gambrel roof. The trusses are
> specially engineered so that no chords are needed (almost like a
> scissor truss). This allows me to use the top of the barn as a loft.
> But, I want to raise the height of the walls on which the trusses are
> supported by 18 to 24 inches so that I have extra head room on the loft
> level of the barn. Normally, the floor joists would stop the wall
> spreading caused by the thrust of the roof, but since I am raising the
> wall height, that is not the case anymore. Will I have a problem if I
> don't add any more supports elsewhere (I am not about to use flying
> buttresses on my barn). One potential solution I have is to use some
> cross bracing from the top of the wall down inward to the floor joists
> at an angle every so often along the wall, like:
>
> /
> /
> /
> |\
> | \
> |----\---------
> |
>
> That way I get the extra head room, and the braces won't be in the way.
> Any thoughts?
>



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