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Skylight Install - Cutting attic joist crossbeams?

Skylight Install - Cutting attic joist crossbeams?


  #1  
Old 08-25-10, 12:11 PM
S
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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:
Imageshack - img5813s.jpg

This is a pic of one of the crossbeams (they are 15' long crossbeams, spanning 11 joists which are 16"OC):
Imageshack - img5814t.jpg

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.
 
  #2  
Old 08-25-10, 01:03 PM
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I certainly wouldn't cut them. You would be playing with the structure.
 
  #3  
Old 08-25-10, 03:23 PM
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There are rafters holding up the roofing. Ceiling joists holding up the finished ceiling below. Rat-runs across the ceiling joists installed to solidify the joists and walk on above in the attic. The rats can be cut as well as the ceiling joists and the rafters. Under 4' wide, you need to double the sides, bearing to bearing, and add header joists. Over 4, dbl sides, and headers. 6 all with hangers: http://www.cciccweb.org/files/Framing.pdf Easier to double existing sides, add headers, add skylight framing. Insulate and v.b. the chase for moisture.

Be safe, Gary
 
  #4  
Old 08-26-10, 08:35 AM
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Thanks for the reply. I had posted in another forum and they basically concur, that those rat runs are not structural in nature and sometimes installed for walking on (and I guess as you say, to solidify the joists, and by solidify, I assume you mean to keep them from shifting and to maybe spread any potential load across all the joists touched by the rat run).

So I will double-up everything properly, maybe as a safety measure and/or peace of mind/overkill, I'll also reinstall the cut portion of the rat runs to span a few of the joists in front of & behind the skylight front/back walls. Then I'll make all my cuts.

Thanks!
 
  #5  
Old 08-29-10, 03:29 PM
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Before you cut anything out, you should have all your new supports in place, including the light shaft framing. or install temporary bracing.
 
 

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