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RE: Roof Sheathing at Ridges

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With a 3 sided diaphragm, why would the attachment at 16" or 24" on center
at the free edge be an issue? The fasteners at this location may be weak at
the ridge but with a 3 sided diaphragm it needs to resist zero shear at this
location anyway. There is no shear transfer along this free edge since all
shear is taken back to the low side and the torsion is taken out by the end
walls.

Whether there is a continuous ridge vent creating a discontinuity or a two,
sloped, unconnected, unblocked pieces of sheathing meeting at the ridge, it
is essentially the same condition.

What I am missing here?



-----Original Message-----
From: John Rose [mailto:jrose36(--nospam--at)earthlink.net]
Sent: Tuesday, August 06, 2002 1:19 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Roof Sheathing at Ridges


In testing pitched (sloped) roof diaphragms at APA, we found that the
ridge joint was critical since both sheathing and framing end joint
discontinuities occur at this location.  In tests of common (flat)
unblocked diaphragms, the framing is continuous at the sheathing side
joint.  Yes, the sheathing attachment can be standard, but remember that
at the ridge, the unblocked edge has fasteners spaced 16" or 24" oc,
typically.  The roof framing joint at the ridge is weak in resisting
shear forces perpendicular to the framing. Therefore, additional framing
and sheathing attachment may be required to resist these forces at the
ridge, and transfer them to the other side of the diaphragm.

I recall talking to an engineer in the SF Bay region about "creaking
sounds" heard near the ends of a commercial building with a pitched roof
diaphragm, on windy days.  We agreed that it was likely that the sounds
were from the roof framing connection at the ridge, and sheathing
fasteners working to resist high shear  forces at this location.
Structural upgrading was suggested to reinforce the ridge connection to
resist shear forces at the ends of the diaphragm.
John Rose
APA (retired)
Tacoma, WA


Jim Kestner wrote:

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