How to deal with a hump in the subfloor

[TNGuy]

I have a ~1/2" hump in the subfloor (spans 2 rooms and a hallway) that was caused by the floor joists resting on a cinder block wall in the basement. The house initially had improper structural support resulting is excessive settling in areas except for where the wall is. Soon after I bought the house I hired an engineer and company to install proper structural support which stopped the settling problem and improved various problems that had existed but they could not get everything back perfect.

I'm in the planning stage of a LVP install job starting in a different part of the house but eventually I will get to this hump issue. As I install LVP throughout the house I will try to fix floor problems as I go.

In the first room I'm thinking about adding 1/2" OSB to raise the height of the floor to deal with issues in the bathroom. The bathroom had ceramic tile and the floor height was .8" above the subfloor. I'm thinking a elevated floor ~1/2" might also help to deal with the 1/2" hump issue when I get to it. Does it make sense to add 1/2" OSB up to the hump on both side and then fill in that area with Ardex?

 

[highup]

What's the current floor construction like? Maybe cut out then sand or level the Hump, then add a second layer over all of it.

 

[TNGuy]

The subfloor is 23/32" OSB over engineered floor joists, which I'm not a fan of.

The highest point of the hump is near the entry door and left wall to a hall bathroom that has ceramic tile installed. The tile floor has a significant level issue, sloping down from the hump area towards a bathtub. I might end up using self-leveling underlayment to fix this room. It appears the 1st owner installed the ceramic tile knowing the slope existed because the only few cracks are near the bottom of the slope next to the bathtub.

 

[C.J.]

You could open up the subfloor and plane down the high joist. Maybe sister something onto it so it maintains its strength after you take off 1/2”. That’s a lot of work but it’s probably the most cost effective option. You’re out a bunch of time but money wise you’re only out some construction adhesive, screws/ nails and a few 2x’s.

Option 2 would be to lay down underlayment up to and around the hump and feather out the hump itself. Underlayment ain’t cheap and patch takes time to dry. Will it crack on you down the road??? Better use some latex

I suppose you could sand the hump down but now you’re weakening one of the structural components of your subfloor system, the subfloor itself. No bueno.

Can you get underneath the house and nibble 1/2” of relief from the underside of the offending joist thereby letting the joist drop and level out with the others?

You mention LVP. What are we talking about cus LVP is kinda a loose term that people use. SPC is rigid and won’t like the hump at all. Some WPC will drape and contour to the subfloor dips and humps. I’d have to see it to know whether that’s even a possibility, or not.

 

[TNGuy]

I'll take a look underneath in the crawlspace and get back.

The LVP is Flooret Modin Rigid Luxury Vinyl Plank Signature.

 

[TNGuy]

I looked at the subfloor and joists from underneath and it looks like the someone (probably the first owner) tried to fix this hump before and didn't do a very good job at it. It's hard to say if a proper repair can easily be done at this point. I would first need to remove the existing flooring and probably remove some subfloor.

 

[C.J.]

I’ll bet my FIL was working on your house and when he got to that one 1/2” spot he figured once you had all your furnishings back in the house that you’ld never notice it so he just kept on going like nothing was wrong. Yeah, ask me how I know. Technically his state doesn’t touch your state, but he’s close. Coulda worked on your place while he was passing through

Anyway, do you or the wife have your heart set on that specific flooring? Look for a WPC product. It’s a lot more forgiving when it homes to things like this. Maybe a touch of sanding, maybe a few layers of roofing felt and stagger the flooring so butt joints don't land on, or too close to, the hump and you just saved yourself a bunch of work.

 

[DarisMulkin]

Sounds like my house. I have a block wall going down the center and it is the high spot of the house the full length. I never realized it before but my friend was going to install laminate down at his house 6 houses away. He found the high spot so I checked mine and yup I have it also. Our houses were built in the 50's so I bet every house in the sub has the same problem