Some observant person is likely to seize this opportunity to remind me that I’m forgetting about the factor of safety… that everything built to code includes a factor of safety of approximately 2.5 (i.e. is 2.5 times stronger than necessary to avoid failure). Why then would cutting just one piece of one truss cause a problem?
That factor only applies to complete, whole trusses. It covers things like an extra large knot in a member, or a gang-nail plate not placed exactly in the right spot or perhaps even a small hole drilled through a member for a piece of wiring.
It definitely doesn’t cover the four-foot hunk of bottom chord I had to hack from one of mine. Even though I analyzed the thing and added two new supports, plus lots of structural straps in strategic places, it was with a thumping heart and sweating brow that I guided my sawsall through that bottom chord. Nothing budged, of course, but cutting a truss is always a nerve-wracking experience.
Not all builders and tradesmen share this opinion. I’ve seen many trusses cut, cored and heavily notched. When this occurs, there are usually ripple effects such as cracking drywall, overstressed adjacent members, caved-in ceilings and other collateral damage. Add to this an outrageous engineer’s bill to design the fix and you have a very expensive repair indeed. Not to mention the outright danger associated with a violated truss.
So, next time your vent pipe or remodel requires the cutting of even one truss member, try to think of a way around it. If there is no other way, get an engineer involved before you cut. His outrageous bill will be less than if you call afterward.
Tim K. Garrison, P.E., M.S.C.E., of ConstructionCalc.com™ has authored a book and several short courses, and lectures on topics relevant to builders. Reach Tim at timg@constructioncalc.com.
The views expressed in this article represent the personal views, statements and opinions of the author and do not necessarily represent the views, statements, opinions or policies of the National Association of Home Builders. NAHB does not necessarily endorse any of the views expressed by the author and NAHB is not responsible for any direct or indirect consequences arising out of the views expressed in this article.
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