enter image description hereWe are going to be laying hardwood in our entire upper floor. The subfloor between two of the rooms is on a bit of a slope. What's the best way to lay the hardwood over this transition. We are going to be laying it longways through the transition since that is the direction perpendicular to the floor joists. Would it be best to run the hardwood up to the transition and put a board going across at the turning point and make a transition? Fixing the subfloor isn't really an option at this point.

Rough Description: The transition is a doorway that is 36" wide in a hallway. The subfloor on both sides of it is pretty flat. So it'll be fine on both sides of the threshold, but the exact line where they meet will be the issue. In the picture you can see the different subfloor transition between the two rooms. It's made of mortar. There used to be a wall there when the addition was put on the house (in the 70s). It's about 8" wide and the level difference is about 7/16" over that 8"

  • How much of a lift is there? A single direction slope is manageable but a peak or valley at the threshold is more of a problem.
    – Matthew
    Apr 5, 2018 at 14:27
  • Over the 8" horizontal area, it's off by about 7/16" vertically
    – Jeff
    Apr 5, 2018 at 15:07
  • I'm still reluctant to post an answer because I can't see the situation very well. I want to know how close the transition is to the nearest corner or doorway in the hall. Are you able to post a photo from closer perspective in the other direction?
    – isherwood
    Apr 5, 2018 at 15:46
  • The transition itself is a corner. It's where the old house and the addition meet. To the right (in the picture) is a closet door. Then the nearest hall door is 40" away from the transition. I'll get better pictures when I'm at the house.
    – Jeff
    Apr 5, 2018 at 16:20

2 Answers 2


Dave Welch may have answered this to a degree But I will put my spin on it.

Break out the mortar bed to expose the subfloor it covers, get either 1/2" plywood which is in reality, slightly less than 1/2" thick and lay it all over the lower floor level bringing it up to withing working distance of the other floor. If that will be too thick, OSB is 7/16" and use that. No need to get anything that is rated as underlayment that will go under a nail down floor. Underlayment is geared more towards vinyl and other thin flooring installs. Screw it down then add your paper and flooring. Re-secure the diagonal subfloor with screws before you add the flooring over the older subfloor.


Get rid of the slope (only time a transition is acceptable is in a doorway-keep an even flow). You have already put down you U-lay anyway. Screw the floor first the diagonal planking. Install Kraft paper (eliminates squeaking) and screw down 7/16" U-lay flooring. If there are any digits or high spots Sand or fill. That is if I'm reading it right.

  • Let me see if I can explain better. The subfloor in the farther room is about 7/16" lower than the subfloor of the closer room. The 8" mortar transition is just a slope the mason guys put in to "level" them.
    – Jeff
    Apr 5, 2018 at 15:08
  • I agree that the slope should be eliminated (minimized, really, as we can't change the physics of the thing), but what is U-lay? Do you mean ULAY underlayment plywood?
    – isherwood
    Apr 5, 2018 at 15:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.