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Old 12-16-2010, 01:32 PM   #1
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Unfinished garage/ ceiling joist under low pitched roof


Hey guys so I am planning on finishing my garage but in order to even start thinking about drywall and what not I need to figure out how to add some 2x8 ceiling joist that will span 20í on either 16 or 24 oc. I beleive the pitch of the roof is 4/12 and the rafters are 2x4ís. As you can see from the photo there isnít much room to have a 2x8 sit on top of the double top plate. Cutting the 2x8ís to match the pitch of the roof will pretty much leave me with very little support sitting on the top plate. Any ideas?
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Old 12-16-2010, 02:15 PM   #2
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Unfinished garage/ ceiling joist under low pitched roof


Look at it this way, the roof rafters sit and are supported on that narrow top plate, so 2x8's pitched to match the roofsheathing will do just fine. I would set the O.C. at 16" though. Drywall in an unheated and possibly humid space will sag and eventually fail at 24-48", plus it will be harder to hang. Also with a 4/12 roof you aren't going to be able to store big heavy objects up above anyway.

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Old 12-16-2010, 02:18 PM   #3
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Unfinished garage/ ceiling joist under low pitched roof


Er, Uh, from the photo I'm wondering if you have any "joists" currently in place. What I am seeing would be the "rafter" to me, running with the pitch of the roof. The "joists" would run parallel to the floor, from top header across to top header. Just placing a joist across this span would not be enough IMO. You would need "chords" to tie everything together and that gets into some engineering or very good SWAG'ing. Another photo would help, but if there are no joists--what keeps the opposite walls from pulling apart? Just wondering, David
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Old 12-16-2010, 03:42 PM   #4
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Unfinished garage/ ceiling joist under low pitched roof


Thanks for the input Grampa Bud. No heavy items up there just a few light xmas boxes. David, I will post more pictures later tonight. There are some doubled 2x4's at 48 oc with some 1x6's forming an X. The 2x4ís have some diagonal braces out of 1x6 board.
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Old 12-16-2010, 09:51 PM   #5
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Unfinished garage/ ceiling joist under low pitched roof


Just drop them with a notch, keeping it under the max. allowed by code, 1-7/8” -Table 1: http://arch.umd.edu/Tech/Structural_..._Guide_A11.pdf

You could taper cut the top a little, enough to get the required number of fasteners to keep the rafter/joist shear connection, replacing the double 2x4 rafter ties: http://www.engineersedge.com/civil_e...onnections.htm

Taper cutting guide lines for joists, pages 32 and 33, Fig.6: http://books.google.com/books?id=iwS...joists&f=false

Gary
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Old 12-17-2010, 02:26 AM   #6
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Unfinished garage/ ceiling joist under low pitched roof


Thanks guys for all the help. Seems like I am on the right track. One last concern that I have is about the boards that form an X (see attached photo). Do I leave them be and just notch the 2x8 enough just to clear them.
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Old 12-17-2010, 02:29 AM   #7
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Unfinished garage/ ceiling joist under low pitched roof


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Old 12-17-2010, 12:52 PM   #8
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Unfinished garage/ ceiling joist under low pitched roof


Those 1x boards were put up there originally to rack the top of the walls square so the roof could be built. Newer construction solved that problem with 1x boards set on a 45 from every corner up or down to the wall top or bottom plate. Still newer construction sheats every outdoor wall corner with a 4x8 sheet of outdoor grade plywood. Unless you are planning to remove or alter your garage roof you should be alright removing those 1x boards.
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Old 12-17-2010, 07:16 PM   #9
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Unfinished garage/ ceiling joist under low pitched roof


As said, remove them as the roof boards perpendicular (on the rafter tops) to the rafters hold the middle area of side walls straight with the new ceiling joists holding the walls from spreading outward. (Unless you live in a high wind area).
GB, I think the picture is on top of the rafter ties, not keeping the walls plumb.......

Gary

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