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Re: RESIDENTIAL: Rafters Not Meeting At Ridge Plate -- Staggered Spacing

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Two thoughts on improper venting of attic space.

1.    Strength reduction of the roof framing.  The 1991 NDS states that
prolonged exposure to temperatures above 150°F may result in permanent loss
of strength.  I have seen something more recent that indicates this loss of
strength may start at 125°F.  How long is prolonged?  Well,....

2.    The warranty on the shingles is probably void.  The excess heat from
the improperly vented attic will "cook" the shingles from beneath, leading
to edge curl and embrittlement.

As for the "rippling effect."  Could it be the sheathing is deflecting
between the rafters?  I've seen this on tract homes with 7/16 OSB over
trusses at 24" o.c.  The sheathing is adequate for load, but sags over time.

Conrad Guymon, P.E.

----- Original Message -----
From: "Bill Polhemus" <bill(--nospam--at)polhemus.cc>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, October 19, 2001 8:07 AM
Subject: RESIDENTIAL: Rafters Not Meeting At Ridge Plate -- Staggered
Spacing


> I am doing a forensic investigation for a "tract home" built by a
well-known
> homebuilder in the Houston area. One of the more surprising things I found
> was that the rafters do not meet (are not collinear) at the ridge plate
but
> rather are staggered along the length of the plate. The spacing isn't even
> regular, but random.
>
> According to UBC '97 2320.12.3 "Rafters shall be framed directly opposite
> each other at the ridge." Obviously we see a code violation here, but I'm
> interested in the implications of this. My assumption is that even though
> the ridge plate might be able to withstand the lateral thrust of the
rafter,
> the roof is considerably less stiff as a lateral load resisting element,
> which could have some problems.
>
> Can someone make any other observations about potential problems?
>
> Also, secondarily the contractor apparently "forgot" to install a ridge
vent
> in the roof. There are only two turbine vents in the entire roof (this for
a
> house with approx. 1,500 sq. ft. of footprint area). Since I'm seeing a
> "rippling effect" in some of the roof decking, I'm assuming that there's
> "bad stuff" happening with excess heat in the attic space.
>
> What are the implications of improper venting of the attic space? Any
> thoughts on this?
>
>
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