How two install hardwood floors in a long room with a subfloor that has a plane change in the middle?

Question

I'm installing 3/4 oak hardwood floors in a long room (45') and the floor is flat, with one exception. The house is a 100+ year old brick townhome with the back half built at a later date. Midway through the room (where the "extension" starts) the plane of the subfloor changes such that a slight crown is created running perpendicular to the direction of the intended hardwood install. There are no signs of recent settlement in the house.

While the angle is relatively slight, due to its position in the middle of the floor, I'm wondering what the best way to approach this is. My current thought is to sand the crown to take the edge off and lay a row of shingles on each side to make the change more gradual. I'm leaning in this direction because previously there were hardwood floors laid in the room and I never noticed a crown in the floor. I thought about adding sleepers, but I worry that fixing the angle over 20+ feet would make the sleepers way too large at the far wall. Does my approach seem reasonable?

Answer 1

Yeah, I would nix the sleeper idea too. Sand away or rent/buy a Power Planer or Belt Sander to take the hump down. Or, remove the subfloor rows (assuming they're running parallel with the hump) & replace them with thinner stock or plywood of the right thickness.

On the flip side, literally, if you have access to the floor structure from below you may find repairs needed there that can bring the old floor up. The old structure may very well be led-in into the bricks will be found to have crushed or sawed-down the bricks or mortar to explain the hump.

The joists would just need to be shimmed up & you may elect to do them all to fix other such deflection issues in the rest of the original house. Be cautious though because fixing the structure can cause cosmetic problems if you find big drops that need actual jacking.

Answer 2

I've been in this situation once or twice. Sometimes I will build up the perimeter to make the grade more smooth of a transition. I have planned and sanded. And I have pulled up subfloor, planned joice down, and paper shimmed low choices, then pre-installed sheeting. It just depends on the severity of the issue.