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jolob · May 19, 2010, 06:10 AM

I need to replace a roof, and have been getting different answers from different roofers. I have a gable roof with a 6/12 pitch, one layer of shingles. Trusses are 24" on center. Decking appears to be 3/8", and appears to be in decent shape, however there is a lot of deflection when walking it. One roofer tells be I should replace the decking; another tells me to put a second layer of decking; a third tells me to use 30 lb felt, and it should tighten everything up. Any thoughts, or insight would be greatly appreciated. Alos, the house is in southern Michigan, so snow is a factor.

ballengerb1 · May 19, 2010, 06:57 AM

3 opinions from 3 roofers, no surprise here. The last guy is not the sharpest knife in the draw so drop him. Felt is not going to "tighten up" anything but it would make it more water proof. Defelection, 6/12 and Michigan tell me its time for a new deck. 3/8" with 24 "oc is not a good combo. 3/8" is acceptable for 12" oc with certain grades of ply. You must check with your building department but I think you will find your current roof does not meet current code.

jolob · May 19, 2010, 05:37 PM

Originally Posted by jolob

I need to replace a roof, and have been getting different answers from different roofers. I have a gable roof with a 6/12 pitch, one layer of shingles. Trusses are 24" on center. Decking appears to be 3/8", and appears to be in decent shape, however there is a lot of deflection when walking it. One roofer tells be I should replace the decking; another tells me to put a second layer of decking; a third tells me to use 30 lb felt, and it should tighten everything up. Any thoughts, or insight would be greatly appreciated. Alos, the house is in southern Michigan, so snow is a factor.

Thanks for the advice.

creahands · May 20, 2010, 04:41 AM

3/4 inch ply on 24'' center rafters/trusses. The deck should be replaced. If u add 1/2'' ply on top of 3/8'' ply, the 1/2 will deflect over time. Long before life of shingles expires.

Chuck

KBC · May 20, 2010, 04:04 PM

I have to disagree with you on this one creahands.

Installation of new 7/16" OSB on top of the 3/8" ply,nailed evenly and properly will be more than enough support, I have done this many times over the 20+ years I roofed.

I would ask the OP this though, are there clips between the plywood?H-clips were commonly used to help deflection between the ply layers.If the new OSB is installed,not even to the course of plywood,but cut to remove the overlapping joints, (If first course of 3/8" is full 4'X8',the the first course of OSB cut down to 3'X8')

This would be more than adequate for a home even with major snow loads,,remember,it has stood this long with the 3/8" only, adding another 7/16" would be a huge improvement, and much less labor to just install,not remove all and replace with new.

Just my humble opinion.

creahands · May 21, 2010, 01:13 AM

Hi KBC

If it was the old 5 ply I would agree with u, but the big box stores carry 4 ply and some 3 ply. This is like installing the equivalent 3/8 plywood.This will deflect.

The 3/8 can be left on but I would install 3/4 over it. The only concern I have is the chance of condensation in the void between the 2 sheets.

I agree with u about having the seams either 1/4 lapped or 1/2 lapped. I would lap the seams both ways. Vertical and horizontal.

Chuck

KBC · May 21, 2010, 02:38 AM

Yeah,the seams both ways, I was tired when I answered:)

'Old 5 ply'?? Is today's OSB not made like it was before?

The gap between the courses I have eliminated(all but),with the use of screws,I can nail the perimeter but the bodies,between the joists where the deflection happens) I would use screws, it really wasn't all that difficult as with flat roofs,screws were commonplace.

Anyway, we both are on the page of installing something over the existing,not just paper(which has to be installed anyway)Ours is just on the thickness and products.

Time for the op to decide:)