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RE: Re: Wood Vaulted Gable Roof Truss End wall

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Richard,
You do have to consider the wall for lateral support normal to the wall -
this is true. However, you need to consider the design to see if my
suggestion works. The same need for lateral support is required if the wall
exceeds it's L/r ratio regardless if you balloon frame or stack. Here are
some things that can effect it:
1. In some cases the vaulted ceiling occurs in the living room only and on
the opposite side of the wall is a bedroom or other room with a lower
ceiling. You can brace the wall from the opposite side.
2. If the wall is common to a vault on both sides, then you need to design
the wall to be braced regardless of whether you create a mechanical hinge or
not if the L/r of the wall exceeds code allowable.
3. With the truss being concentric to the wall, the truss can be designed
for the shear that you need to transfer the load from the top chord to the
bottom.

A truss is designed to be a drag truss. The truss manufacturer (assuming you
are using a fabricated plated truss) will apply the lateral load that you
need in the line of shear and either confirm that the truss has the capacity
to transfer the shear from the top chord to the bottom chord via all the
truss members OR might need to "beef up" the truss to accommodate this. It
is also common for a truss manufacturer to recommend a double truss when the
shear capacity of the truss is known but less than 1/2 of what you need.
Specify the drag capacity on your plans and make sure that the truss
manufacturer has taken this into account when you review his truss package.
The connection to the wall is mechanical. I generally use A35 or A35F from
the top plate of the wall to the bottom chord of the truss. You need to be
sure you specify that the contractor not try and nail the mechanical
connectors through truss plates and that he insure that he not split the
truss chords. I have not found this to be a problem in most designs.

Generally, I have seen 2x4 plated trusses with 2x4 diagonal web members that
are good for more than 3,000 lbs. - but this needs to be calculated by the
manufacturer based on the capacity of his proprietary press plates.

Dennis

-----Original Message-----
From: Richard Lewis [mailto:rlewis(--nospam--at)techteam.org]
Sent: Tuesday, November 09, 1999 5:52 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Re: Wood Vaulted Gable Roof Truss Endwall


Dennis,

I would like you to clarify your note here.  I understand it to state you
run
a horizontal wall plate and then horizontal/flat bottom trusses.  You would
do this for cathedral type ceilings?  How to you account for the hinge in
the
wall where the top plate is horizontal, yet there is no lateral support for
the wall at the joint?

Also, what make a truss a drag truss?  I have never heard that term before.
Are the web members different from a typical truss?  Do you use a fully
studded end truss?

Rich


seaint(--nospam--at)seaint.org writes:
Ed,
If the wall is parallel to the truss, I routinely request additional trusses
and have them designed as drag trusses. This makes it much easier to build a
conventional plate and transfer shear through a conventional truss down to
the shearwalls below.
It seems to be worth a few extra dollars to manufacture the trusses special
and to insure their capacity in shear rather than try to panel up a pony
wall or balloon frame - even if the vaults are scissors and you need only a
couple of conventional horizontal bottom chord trusses for the sides of the
vaulted room.
I am not sure if this is what you are looking for. Almost every home with a
sloped roof in my area is done with plated trusses. It is simply more
economical and easier for the contractors to set up.
Regards,
Dennis S. Wish, PE


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Richard Lewis, P.E.
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rlewis(--nospam--at)techteam.org

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