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spup345 08-25-2010 02:09 PM

Skylight Install - Cutting attic joist crossbeams?
I'm going to be installing a skylight in the middle of this picture, cutting through the middle joist. That means that I'll have to cut through 2 "crossbeams" (I don't think they are called rat runs because I don't have a truss), here is a pic:

This is a pic of one of the crossbeams (they are 15' long crossbeams, spanning 11 joists which are 16"OC):

They are on the other side of my attic as well, 3 of them, 15' each, spanning the entire length of my house, overlapping on a joist as you saw in the first pic.

My questions:
1. Am I allowed to cut them?
2. If yes, what do I need to do before & after I cut them (i.e. Put additional ones on? Full 15' ones, or just long enough to span a few joists? Move the entire 15' existing ones instead of cutting them?)?

Keep in mind I'll be splaying the skylight front/back so if I need to replace the crossbeams, they will not be in-line with the existing ones, they will be several feet closer to the middle of the attic and/or several feet closer to the edge of the roof to make room for the splayed skylight walls. And yes, I know I need to deal with all those wires that are in the way, fun fun fun.

spup345 08-26-2010 10:41 AM

Got my answer elsewhere. Basically, they are rat runs, not structural in nature (helps folks walk in attic and solidify joists), can just put a couple of additional ones in front & back of the skylight walls spanning 7-8 joists, then I can cut the ones in the picture and double-up everything as needed for the skylight frame. Thanks.

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