Existing roof is a 3 tab shingle with 1/2" plywood.
The nails used are 1/2"-3/4". Most of the nails do not come through the plywood. The roof/structure is completely open and can be seen from underneath. It is outside in a yard. Seems 1 1/4" nails are recommended. Roofs been on quite awhile and the nails held ok. Will the 1 1/4" nails rust since they will be below the plywood? Or should the shorter nails be used again? Thanks for any help.
the nails should penetrate the wood
they won't rust you'll just see them popping thru everywhere. The short nails will work if you are worried about appearence, we have to use them quite often on exposed overhangs and the HO doesn't want to see all the penetrations with no problems
The specification for this states that on plywood or OSB roof decks, the nail shall penetrate past the point with the shank exposed. On lumber type decking, then a minimum of 3/4" penetration and a irregular nail shank.
This 3/4" spec is most used 'round here for exposed decorative tongue and groove decking.
1/2" is too small. Don't know that I've ever seen a half inch roofing nail. Use the 3/4" and just 6 nail the shingles.
yeah, I just assumed he was guessing and it actually was a 3/4 or 7/8 nail. We normally use the 7/8 for that type of situation, can't remember ever seeing 1/2" though they do all look short as hell
Were the same in this situation 7/8 nail
1 3/4" without a doubt under normal circumstances.
Even with new work I use 1 3/4".
Only time I'd use anything less would be for exposed ceiling decking where the the nails couldn't protrude past the bottom of the deck.
Try pounding 1 nail through the roof of each size and see which one doesn't go through in an area that is inconspicuous. That's the easiest way to find out your particular needs.
Just looked at a 60 square roof. Dimensional shingles installed with 7/8" coil roofing nails. I was called to fix five leaks (not our installation) and I found nails backing out from the plywood was the cause. I didn't count them but there had to have been at least 100 nails. Roof is about 14 years old and they didn't want to replace it just yet. I gave them a price for a new one and advised them to keep the buckets handy.
So I would recommend they penetrate the plywood. How big is the roof? We added sheathing on a gazebo to allow proper length nails without penetrating the exposed tongue and grove. With exposed plywood some type of soffit system would hide the nails and look better than the plywood.
I have always used 1 1/4 except when im installing cap over a ridge vent I switch to 1 1/2 nails. the owens corning ridge vent is pretty thick compared to a few others we have installed so thats why I switched to 1 1/2
Yup... gotta go through plywood... lumber decks are different as far as grippage.
Thanks to all who responded. Probably will go with the 1 1/4"