Flattening a floor for LVP install

[user 9818]

Would anyone have feedback for the flooring situation I have, described below?

When our house was built, they made the foundation perimeter at least 1/2" higher than the central beam running across the basement. I can see this where the central support meets the perimeter wall. The beam itself may not even be flat either -- it doesn't look like it settled because there are no cracks in the walls.

The floor is supported by engineered trusses 24" oc.

I know I need to flatten this in some way. When I tiled the other half of the house, it was on a cement slab, so I could grind down high spots and fill in low spots.

The LVP we're looking at is from Shaw and is about 3/8" thick.

I have been searching for solutions and so far have come across 3 ideas:

1) Self levelling cement. Not sure if I really ought to have this done (more than I could handle myself). Again, the center will be at least 1/2" or more lower than the perimeter and I have no idea if that much cement is a good idea, or even if it could crack and not be good below the LVP. Probably need another layer of plywood on top of it anyway? Seems like trying to attach the layer of ply would crack the thin cement.

2) Fill in everything with layers of thin ply, felt pad, or something, then put some thickness ply on top of that.

3) Fill in only above the trusses, then put down ply (3/4"?).

Are any of these on the right track? Are there other suggestions? More info needed?

When the kitchen contractor tiled the kitchen years ago, he ignored the non-flat floor, so any remedy I do will now have a rise of some height from the kitchen to dining room. Stuff like this is why I started doing it myself. We really don't want to put carpet back in, but at least that is more forgiving of a nonflat floor.

Thanks in advance for anyone taking the time to read all taht and possibly give feedback!

Also, if there are pointers to information I should study some place, I would be willing to follow up on that too. There was certainly plenty of reading I did before tiling & I'm happy with how the 8" x 4' planks turned out!

Andy

 

[Incognito]

My career was in commercial vinyl/rubber/lino/VCT/Glue down carpet/carpet tile.

MOST of my time was spent flattening and smoothing out sloppy concrete. Commercial installs go super fast. Prep is a MF'er. I have not nearly so much experience with wood substrates/structure but i think I can steer you in the right direction. Solve structural and elevation issues with wood using shims, felt and layers plywood. Depending on the LVT there's generally still MINOR patching you'd want to do with cementitious underlayment (Ardex Feather Finish) on the seams and fasteners, if needed.

I'd aim for the topmost layer to be 1/4" underlayment grade plywood. If your shimming/felt/STRUCTURAL layers are done well that topmost ply underlayment can be butted together, stapled down and would require ZERO floor patch on top. It is the more time consuming method compared to self-leveling, which is certainly an option------just not my preference.

Super hard to detail the explanation as to where you want the shims, felt, structural layers and underlayment thicknesses absent a topograghical map along with a blueprint with details and specifications. In reality we're just going to go with our gut and experience in any individual case to get those conditions up to snuff.

So you know, LVT is one of the more "installer friendly" products in the hard surface field. When it's all too much and a customer can't afford proper prep we recommend carpet tiles. That's probably the least challenging to prep for.

 

[user 9818]

Thanks -- it looks like your vote is for option 2: fill in everywhere with various ply thicknesses, felt, etc., then add a final top layer of 1/4" ply.
The advantage of that vs option 3's wide strips over the trusses + 3/4" ply for the top, is it would result in a lower final height due to only needing that 1/4" top layer.

 

[JPfloor]

Option 2&3

Get yourself some string or better yet a laser level. Fill in all the low spots with 1/2 plywood, 1/4 plywood, roofing shingles, door skins, felt paper and whatever else you can think of to get it flat… Then cover with a layer of 3/4” Plywood… You can’t just put 1/4” over all that shimming. 1/4” is underlayment designed to obtain a smooth surface. Not much structural value.

P.S. Not real thrilled that the joists are 24” OC… How thick is the existing plywood?

 

[user 9818]

Existing base is 3/4". It's probably nailed, so after the carpet and 1/4" ply under that is fully removed, I was going to screw the first layer down before other additions.

OK, so maybe the 1/4 on top the the shimming was too hopeful.... Is there a need for yet another layer of 1/4 underlayment on top of the 3/4 on top of the shimmed area? As I mentioned, the Shaw LVP is 3/8" & they say it doesn't have to have all minor imperfections/gaps and such filled under it, since it is pretty stiff to start with.

 

[JPfloor]

No. Shouldn't have to. You could go with a CDX grade 3/4" ply if you can find it.. That will give you a smoother surface.

1/4" underlayment would only be if you were gluing down the finished floor.

 

[C.J.]

I like option #2 but would be ok with option #3.

 

[user 9818]

Thanks for all the feedback so far. Sounds like #2 is mostly preferred, with #3 an option.

And, I'll definitely be getting a laser level rather than crawl around with my 10' level!

 

[user 9818]

I'm sure the rest of you are used to this type of thing, but it is new to me -- after finally getting all the 1/4 ply off, I realized that where I thought they might have put another layer under a few spots was actually just different heights on the subfloor ply. And, looking closer at the engineered trusses, I see that many aren't so much bowed from weight as warped by the 2x4s used in them as they dried, I suppose. Thus, the subfloor plywood is uneven plus the trusses rise and fall individually, all on top of the foundation being higher than the central beam.

I might end up with option 3 (building up over each truss) because height varies from one to the next, side to side + front to back.

Is this really that usual in houses??

 

[user 9818]

I see mention of roofing felt as one of the thinner fill-ins. Doesn't that have asphalt, tar, or the like? Is outgassing from that not an issue inside the house?

 

[JPfloor]

I see mention of roofing felt as one of the thinner fill-ins. Doesn't that have asphalt, tar, or the like? Is outgassing from that not an issue inside the house?

Unless you have a roll from 1960 it should be safe. No carcinogens that we know of.