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RE: factory-made roof trusses

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Roger brings up some great points. One point I wanted to comment on. The
fabricators out here use #2 grade lumber. However, I just did an inspection
on a job where I specified #2 grade DF for roof rafters. The quality of the
lumber was awful. Full knots in each edge, some voids were knots used to be.
I'm now sticking with #1 grade or better. BTW, each piece I inspected was
graded and stamped. I could not believe that any member would be allowed to
have a 1-1/2" diameter know in either edge.
Guess I need to specify on my plans to disregard the direction of the crown
and pay attention to which side the knot appears.
Dennis Wish PE

-----Original Message-----
From:	Roger Turk [mailto:73527.1356(--nospam--at)]
Sent:	Saturday, August 01, 1998 11:04 AM
To:	seaint(--nospam--at)
Subject:	factory-made roof trusses


Get a copy of MasterSpec Section 06192 (Metal-Plate-Connected Wood Trusses)
from your architect-client.  MasterSpec is licensed, otherwise I would offer
to send you a copy.

Since most pre-fab truss fabricators use computer analysis provided by the
plate manufacturer, which kicks out *anything* that is permitted by the
I would specify that only No. 2 or better grade is to be used.  (I have seen
No. 3 called for on their calcs and I have seen No. 3 in lumber yards --- No
way would I ever permit No. 3 to be used on any of my jobs, except as

Make sure that you clearly specify the loads that are to be applied to the
top chord and the loads that are to be applied to the bottom chord.  I
investigated one failure where non-structural wood box beams at 6' centers
were connected adjacent to every fourth truss, causing the web member to
chord connections to fail.  (The trusses also lacked lateral bracing of
compression web members --- see next paragraph.)

Designs that I have seen typically will not spell out lateral bracing of web
members in compression.  I specify that *all* bracing that is required as a
condition of design is to be clearly detailed on the fabricator's plans.

Be aware that truss fabricators are neither licensed, trained nor franchised
by the metal plate manufacturers.  The metal plate manufacturers merely sell
the fabricators the metal plates and the engineering.  Therefore, the
of work produced by different fabricators can vary tremendously.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

. > I have a project for which I need to specify pre-fabricated wood roof
. > trusses (gang-nailed, pronged side-plate, or whatever is the current
. > least-cost roof- framing method). This is something I haven't had to do
. > before and I have no data or names of manufacturers. Any recommendations
. > on sources or fabricators, and design data?
. >
. > Nels Roselund
. > Structural Engineer
. >