wavy appearance of roof between trusses

I'm not a builder, but can't you get into the attic to check if the 5/8 inch plywood is broke?

I think I would tend to believe the roofers on this one.

Good luck,
Devildog

It isn't 5/8ths, sorry, it is more like 3/8ths plywood. A roofing consultant visited today and felt the roofers could have caused damage, but that it was a hard one to prove if it came to court. All in all, the new roof looks worse than the old.

Any more opinions?

The building code in all locals I am familiar with will not allow plywood less than ½” thick for a roof. When ½” plywood is used it is also generally a code requirement to use metal “H” clips between the sheets of plywood at approximately mid span between the rafters or trusses. The problem with ½” plywood is that it tends to bow a good deal between the trusses and causes the wavy appearance you are most likely seeing. The chances are that you just never noticed it before, and did now only because of the recent work you had done.

If you can get at the underside of the roof from the attic you can install 2x4 blocking to push the plywood up where it is dipping to help straighten it out.

Glenn www.consultationdirect.com

3/8 inch plywood has three plies and two glue layers holding it together. If the wood has been wet, we often see the glue weaken, and any load on the wood then breaks the remaining glue, causing partial delamination and on occasion, complete delamination. It used to be (minimally) acceptable to use 3/8 plywood, and builders who used it to reduce costs also usually used cheap trusses spaced 24 inches apart. With so little support, and with the effect of moisture, the plywood often warps. When someone walks on the roof, the panels deform, and have no internal strength to return to their old level, which is why the roof looks wavy after the roofers finished. The problem is not the roofers, but the fact that your sheathing is below what is acceptable. In such situations, I recommend removing the existing sheathing and resheathing with 5/8 plywood or better. At the same time, you can correct any ventilation problems that exist.

If you're not in the snow-belt, you can probably get away with not resheathing until the next reroofing job. However, I suggest you periodically check on your sheathing from the attic to make sure no further deterioration is happening.

Best of luck
Paul

I'm not a builder, but,

I like Glenn Good's suggestion about the 2x4 blocking. Obviously you don't want to reroof after just having it done. Try the 2x4's in one area and see if it makes it look better. It might take a while, but it's a lot cheaper.

Keep this in mind when you want to get up on your roof. If the posts are correct I don't think I would walk up there. Maybe take a wood plank up with you and lay parallel to the peak. Walking on the planks will keep you from falling through.

Good luck,
Devildog

The problem is caused by the deficient undersized plywood you started out with, but the "roofers" are not completely innocent. Not legally but from an ethical business standpoint.

IMO, they should have noticed the lack of structure, notified you, and given the option for you to agree to a change order to replace the plywood.