I'm not floor guy though did work for one right out of HS for several years.

I'm installing cabinets in a semi-custom home, and the homeowner has asked me if this is going to be a problem. The upstairs floor where it is to receive 5/8" engineered hardwood, looks like the pacific ocean. The sub floor is very uneven and you can feel the high and low spots in it. it is 3/4" thick 6" diagonal sheathing with 1/2" ply over that. Can the floor be leveled out, or can the hardwood be installed over it as it is, also is glue or staple down installation appropriate. She tells me the contractor does not want to level the floor and is planning on stapling the hardwood to the wavy sub floor.

Just trying to comfort a customer,
Michael

Standard manufacturer specifications for most wood floor installations are that the substrate (subfloor) must be FLAT within 3/16" within an 8' radius. Since the subfloor is wood, I'd recommend sanding down the high places and filling in the low places to bring the floors into specs. Since the whole area is wavy, I'd suspect uneven floor joists. This repair may be out of the installer's abilities to correct but he is responsible to see that it is done. He is NOT responsible to pay for it or do it himself. He responsibility lies with making sure the substrate meets manufacturer's specifications. He may insist you take care of it, if you are the general contractor. It's a pain, no matter how you look at it. If you are the GC, I'd suggest you make sure this is taken care of. After the floor is laid, there's no going back with an easy fix.

Gary you are correct most of the joists are crowned severely. Can a self leveling filler be used or would it crumble only he nails down the floor? Being the GC I doubt the homeowner is in a position to want to pull off the sub floor in order to plan e down the joists, though that would be a nice add to my contract.

Michael

Cement based fillers will most likely crack and crumble if one drives fasteners into them. If the floor is an engineered, it can be glued down with the appropriate adhesive over flooring "patch". Oftentimes, many floor patching compounds need to have their specific primer used first, for good adhesion to wood. The installer will grumble about gluing down instead of nailing. Stapling/nailing is much less expensive and for many installers, faster. Expect the installer to charge extra if he needs to glue the flooring down.

I did a nail down floor about 1.5 yrs ago where the wood subfloor was WAY off. It dropped an inch+ in 4 feet all along one 20 ft. wall. The other side of the room wasn't much better. I ended up adding plywood and tapering up the thicknesses and even then, spent a day sanding down crowns and smoothing the plywood out. It was a pain but worth the effort. The customer needs to bear the cost of these repairs OR sign a liability release holding everyone not responsible. Another thing, failure to flatten the subfloor will void any manufacturer's warranty. I also just went through this with a Bruce floor. The complaint was overwood/underwood on the end butts. The subfloor was 3/4" OSB but had a large crown down the middle, right where a large glue-lam was located. I explained to the customer that to properly fix the subfloor, I'd have to remove some of the subfloor and plane down that glue-lam. They didn't want to pay for the work so I installed the floor. Then they complained about the end butts so I had the Bruce rep out. The rep voided the warranty due to the crown in the subfloor that the customer would not pay to fix. This kinda crap comes back to haunt the installer because the customer thinks the installer should have miraculously been able to install the floor without problems. And that anyone problems are the installer's fault. I run across this frequently; people not wanting to pay to properly repair their subfloors then expecting their flooring to perform well. All I can say is: fix the subfloors or you'll be sorry.