Pretty much, any alteration to an engineered truss requires approval of the manufacturer or a competent authority (licensed professional engineer). No holes, notches, cut, etc. without written permission. Engineered beams - LVL and the like - are the same story. They usually come with installation instructions showing allowable holes.
Re: Trusses#153616 10/23/0304:06 AM10/23/0304:06 AM
all excellent answers .it is amazing what forms of truss butchery an inspector sees during framing inspections.one person had to remove the roof and start over.they were not happy campers. sometimes the engineers cannot design a fix as was the case.think before you butcher!
Joists were a different story. One carpenter I talked to, said joist manufacturers had guidelines. It was a simple math thing. Size of hole, number and spacing of holes, width of joist, distance of holes from center or end, span of joist.........etc.
It sounds confusing, but the math is like sizing conductors for pipe fill.
When we rarely had to go through a truss, we told the carpenter the situation, and he either 'boxed' out a section or showed us a better route.
Joists are one story, but I feel one should never, ever, drill a truss!
Unless designed otherwise, the truss frame construction supporting the floor of an attic are not designed to carry much of a load. I do not have my book here, but I will try to read it at work and let you know.
When running wire in an unfinished attic, lets not forget about 320.23, especially since drilling is not an option! Pierre
[This message has been edited by PCBelarge (edited 10-25-2003).]
Pierre,since you brought up 320.23,I am always scrambling to comply with this one. A lot of times the framers will put an attic acess in after I'm long gone. And it always seems to wind up where I presume to be the least likely place,and of course right next to several wire runs that would have been way out of the way otherwise.