Before starting my first hardwood install I found this forum and it answered a lot of my questions. Thank You.
After looking through the forum, I see shingles are my choice for some floor leveling. My question: Doesn't the grit on the shingles cause noise or break down after a period of time? In one area, I might have to stack 2 to get it level.
Plus is there a maximum area that can be covered?
Thanks for all your advice,
Scott

The cheap fiberglass 3 tab roofing shingles can be used to fur up low spots. I place the mineral side down and staple the shingle in place with a hammer tacker. These singles can be used under 3/4 hardwood flooring and under plywood underlayments as well, to raise up and flatten low areas. I would not exceed three in stacking however, nor would I use them for a thin, nailed down floor, like Bruce Natural Choice. They should not "break down" over time. I mean, they are made to go on a roof and last many years. I have never had them "make noise" either. I suggest you give it a try. Feather out the edges of the shingles with layered up asphalt felt paper if hardwood will be going directly over the shingles. This will smooth the transition to the subflooring. Maximum area covered? With the shingles? No, I don't think so. But let's say you had 500 ft to install and 200 ft of it was an 1/8" low. And that 200 ft was all in the same area, like an addition or something. I'd then look for something easier to use, like door skins. Or, just gently taper the higher area down to the slightly lower area. If the areas are random throughout the job, then yeah, shingles work good for that. Some guys prefer thin plywood but in my experience, it is more difficult to work with, with lots of sanding required.