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Old 09-20-2009, 08:03 PM   #1
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Roof Sheathing Thickness


Is there any reason that I would want to use 3/4" sheathing?
I'm building a the roof (hip) for a small addition (8x11) and am finally ready to sheath. The rafter spacing is 14"OC and unless there's a good reason to use 3/4. I'd rather use 1/2 simply because it's a lot easier to hump up to the roof. Do builders use 3/4 on new houses?
I've been working on this far too long with all the crap weather we got early and sporadically through the summer.
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Old 09-20-2009, 08:05 PM   #2
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Roof Sheathing Thickness


hmmm, dunno code, but i'd be concerned about snow weight.

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Old 09-20-2009, 08:11 PM   #3
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Roof Sheathing Thickness


I use 1/2" on sheds etc only
House is all 3/4"

Pretty sure 1/2" is ok for 14" OC, 3/4" is up to 24"

But I have always felt that 1/2" flexes too much when I walk on it
Not that you walk on a roof all that often
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Old 09-20-2009, 09:30 PM   #4
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Roof Sheathing Thickness


1/2" is standard around here. A lot of guys use 5/8" or 3/4" on the overhangs so the roofing nails don't show underneath.

Check roof loading, 3/4" is heavier than 1/2". It's a pretty small difference, but if it's trusses and they were designed for 1/2".....

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Old 09-20-2009, 09:49 PM   #5
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Roof Sheathing Thickness


1/2" would be fine for what you are doing - IMHO.
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Old 09-20-2009, 11:05 PM   #6
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Roof Sheathing Thickness


No, builders do not use 3/4" on houses unless they have to. In 36 years of framing houses, only one I had to use 3/4" , at the base of Sea-Tac Intn. Airport, and that was for sound, not strength. 3/4" ply will span 36" between supports. Most builder's use 7/16"osb with clips if a heavy roof covering applied or called for on plans. Otherwise, no clips, just be sure to space all edges 1/8" as listed right on the sheathing (label), which goes down so the inspector can read it from inside (it's also the waxed side which is safer).
Read the first numbers listed 32/16, means 32"span on roofs, 16" span on floor. http://books.google.com/books?id=bwt...20span&f=false
Be safe, Gary
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Old 09-23-2009, 11:18 AM   #7
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Roof Sheathing Thickness


Does anyone use t&g planks anymore?
For this small roof, this might be easier because every sheet of plywood would need to be cut to fit the hip roof anyway.
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Old 09-23-2009, 02:06 PM   #8
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Roof Sheathing Thickness


1/2 inch sheathing on 24" centered trusses is commonly used here where snow load is 30 pounds. So I would think it's plenty at your 14" rafter spaces unless you have unusually large snow loads.

I find it easier to nail down whole sheets on the roof letting them run wild past the hip ridge, cut in place to match the hip ridge and finish nailing. You run one whole side, snap a chalk line and cut it off and go to the next side. Save the valleys for last because they have to be cut before nailing and are easier to measure after the rest of the sheathing is in place. Since the valleys tie into the existing old roof chances are they won't fit if you use theoretical measurements so just measure the actual length at top and bottom of the sheet.

The only drawback is that the sawdust can get pretty slippery. Use a fall restraint system and take a nozzle for your air line (if using a nail gun) so you can blow the dust off the roof after each cut.

And make sure no one is below cause the cutoffs likely will slide right off the roof as you cut.
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Old 09-23-2009, 02:13 PM   #9
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Roof Sheathing Thickness


Not for over 20 years..... When you cut the hip angle, the waste piece fits the other side perfectly, just don't install with strength axis going wrong way (watch the arrows on the label side goes down). Try to cut the angles in mid-sheet so the remainder waste will work for a 1/2 sheet angle on the other side of hip. Then most of a full sheet will work with snubbing the corner off.
Be safe, Gary

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