Yesterday I called Unirac, and was told that the only time they had
heard of this issue before was when the trusses were made from glue
lams. They have heard no complaints of truss failures. I'm sure
installers would have let them know.
We are planning to use 5/16" lags, which I doubt would be a
problem. I think our Truss mfg is being overly territorial.
-Drake
At 03:28 PM 4/27/2010, you wrote:
Hi Drake and all,
We have had both engineers and inspectors question the use of a 3/8"
4" lag in a 2x4 top chord and I think rightfully so. When we have a
chance to spec new construction we have the architect replace the
2x4 top chord with a 2x6.
And when we have to go into 2x4's we either shorten our lag to a
5/16" 3.5" or even 3" (if we can get away with it on the uplift
calcs) so we stay in the top half of the wood fibers on the
truss. We have also sistered or blocked 2x4s when there was concern.
But like Bruce said - I cannot imagine there ever being a problem
with a 2x6 with a 4 " lag (only 3.5" of which goes into the wood)
unless you were using 1/2" lags!
The real issue is in installation. Installing a lag so that it
glances the side and splits the rafter or hitting a knot and not
backing off could cause problems. So we are really careful in
installation to make sure we are right on the center of the truss -
we drill tiny probes everytime - that's where the real issue is -
once engineering is happy of course.
Hope that helps!
Jeff Clearwater
Village Power Design
Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648
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