Roof clips
Coopsdaddy
| Posted in General Questions on
Our roof will be 12/12 pitch with 2×6 raifters,would it affect much if we changed to 2×8 to fit a little more insulation,also our roof deck is 7/16 osb taped with a 1.5-2 inch polyiso nailbase on top if that,do you think we need roof clips on the first layer of osb or need to change that to 5/8osb?
Thanks
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Replies
Quinton,
Who sized your rafters? Most rafter span tables start with 2x8s. Using reasonable criteria (with one online span calculator), I came up with a span of 10'10" for 2x6 rafters. That's not much. Your criteria may vary. In any case, if you end up using 2x6s, make sure the span isn't excessive.
There is no down side to choosing deeper rafters other than the increased cost. Deeper rafters are stronger and provide more room for insulation.
The thickness of the required OSB depends on your rafter spacing, which you didn't tell us.
In a cold climate, 1.5 inch polyiso should be considered as having an R-value that is no more than R-7.5. Unless you are filling your rafter bays with open-cell spray foam, I hope you live in Climate Zone 3 or somewhere warmer. If you live in Climate Zone 4 or somewhere colder, you need thicker rigid foam above your roof sheathing. For more information, see How to Build an Insulated Cathedral Ceiling.
I don't know how either of you can size rafters without knowing the span or loading criteria: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_8_par027.htm?bu2=undefined
Michael,
In my response, I noted, "your criteria may vary," and I urged Quinton to double-check everything to make sure that his rafters were properly sized.
So I agree with you -- anyone who is sizing rafters need to know a lot of factors, including wood species, grade, rafter spacing, and snow load -- and Quinton didn't provide us any of those factors. I wasn't sizing the rafters for Quinton -- I was urging him to double-check his sizing method.
The building code also dictates (or offers guidance, depending on your situation) about the use of panel clips. See "with edge support" and "without edge support" in this chart: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_5_par041.htm?bu2=undefined. 7/16" sheathing is allowed for spans up to 24" without clips, provided its span rating is 24/16 and you're not in a high wind area. I would not use 7/16" in most cases but it may be ok under nailbase.
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The house is 24wide by 42long,12/12 pitch,we are in zone 3.I will post a pic of the truss when I get home today.
Thanks
If they're trusses that changes everything, including how you'd insulate.
There story and a half trusses 24 on center,I would like to do 3.5-5.5 inches of oc foam and some cheaper stuff on top I that,than finish off insulation with polyiso on top of unvented roof.
after talking to john manville they don't even offer a fastening diagram or tech advise for a 12/12 pitch.
Im going to meet with the contractor about changing the rafters,maybe even 2x10,
Can something like this be a option,without the nailbase and vented soffit and ridge cap?
Owens Corning R-38 Cathedral Kraft Faced Insulation Batts 23-3/4 in. x 48 in. (8-Bags)
Description
GreenGuard GOLD certified & verified to be formaldehyde free
Offers thermal performance for cathedral ceiling applications
Helps homes stay cooler in the summer and warmer in the winter
ModelK91Internet/Catalog:205469706
The rafters in cathedral ceilings are usually made of 2x10 ft. or 2x12 ft. and Owens Corning EcoTouch high-density insulation products are designed specifically for these rafters. R-30C and R-38C are available in both kraft-faced and unfaced. Owens Corning EcoTouch insulation delivers comfort - helps homes stay cooler in the summer and warmer in the winter. It will help reduce monthly heating and cooling costs for the life of the home and offers exceptional thermal and sound control performance.
Dimensions: 9-1/2 in. x 23-3/4 in. x 48 in., 8 pieces (63.33 sq. ft. / bag)
8 bags/pallet = 64 pieces/506.64 sq. ft.
Application: Cathedral ceiling
Designed to eliminate R-value loss caused by compressing standard R-30 products in 2x10 cathedral ceiling construction
Provides 1 in. of ventilation air space between the insulation and roof deck
Insulation will not slump within the cathedral ceiling cavity