Basement subfloor questions

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rb1987

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I am in the process of remodeling my basement. There used to be carpet with padding down. When I ripped it up there was no evidence of mold so my slab isn't letting moisture in. The slab slanted though and I was told to do click lock flooring you need a mostly flat surface. So I hired a contractor to put down some self leveling concrete.

I don't know what happened, but some areas cracked and some areas have some flex (like around 1mm) and sounds like air is under if you hit with a hammer. I don't trust the structural integrity of this to put my flooring directly onto this. I suspect incompetence, they walked away refusing to fix and returned my money (thank god). Its been a hassle trying to find someone to fix it. About 250sqft. of the 700sq.ft. put down could use some chipping away and patching.

A few ideas were floated to me and they both have pros and cons.

First, let me start by saying that this is mostly aesthetic basement remodel that will see minimal use. But I still want it to look nice. The basement is heated and cooled via a heat pump. I am putting in new knee walls around the perimeter, new R21 wall insulation via XPS and R15 Mineral Wool, new doors and a new ceiling.

Idea #1 - Using dimpleboard like DMX 1-step and then use (2) layers of 7/16 OSB on top with the joints staggered 6" and both sheets screwed together so they are one huge, sheet and float this. This requires no tapconning into the existing slab. Pros are that this provides a solid structure. Cons are cost and reducing floor to ceiling by 1-1/2". This option will likely involve modifying last step (steps arent up to code anyways, but are grandfathered in) and will require raising up the one existing door.

Idea #2 - Using DMX 1-step and putting flooring directly over this. I like this because it is cheapest, easiest and will only reduce floor to ceiling by 1/2" and I wont have to adjust my stairs and existing doors. Cons are im not sure how much structure it adds if any.

Idea #3 - Laying PT 2x4s flat on the ground and putting 1.5" XPS between them. Then running OSB over this then doing my floor. This will add floor R7.5 value, which I like and this will add structure. What I don't like is this has no air gap underneath and this will reduce floor to ceiling height by 2-1/4 at least and stair will have to be modified and one existing door will require raising up.

The floor going down is 8mm Corelux LVP.

Current floor to ceiling height is 84". Code in my area requires at least 80" for existing basements so all options are code compliant. My thing is losing 2"

I know this is a lot to take in, but i'm so uncertain on how to proceed. Appreciate the time you took to read this.
 

rb1987

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Also -- being that the DMX is a vapor barrier, how should this run out to the exterior?

How I plan on doing walls is Loctite Powergrab Heavy Duty the 1" XPS directly to the concrete, 2x4 wood construction with unfaced R15 mineral wool between the studs. Where should a poly wall vapor barrier play into this wall construction and how should it get flashed to the DMX to prevent any water vapor from under the DMX going into my wall cavities? Would XPS, then a poly vapor barrier lapped and tapped to the DMX and then my 2x4 wall construction work or will moisture just get trapped between the poly and the xps?
 

wwhitney

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I am in the process of remodeling my basement. There used to be carpet with padding down. When I ripped it up there was no evidence of mold so my slab isn't letting moisture in.
I didn't read your entire post, but I'd like to point out that the above isn't necessarily true.

What you reasonably can conclude is that the rate of vapor release by the slab, along with the permeability of the carpet and pad and the ambient humidity in the basement, didn't cause the relative humidity within the pad or carpet to exceed the threshold for mold growth. If you put down a less permeable product, you could cause the relative humidity under the less permeable product to be high enough to allow mold, if there's anything moldable underneath the less permeable product.

So I would think it's worth doing the "tape down a square of vapor barrier" test to see what kind of results/condensation you get. Although I'm not knowledgeable about how to interpret those results.

Cheers, Wayne
 

rb1987

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I didn't read your entire post, but I'd like to point out that the above isn't necessarily true.

What you reasonably can conclude is that the rate of vapor release by the slab, along with the permeability of the carpet and pad and the ambient humidity in the basement, didn't cause the relative humidity within the pad or carpet to exceed the threshold for mold growth. If you put down a less permeable product, you could cause the relative humidity under the less permeable product to be high enough to allow mold, if there's anything moldable underneath the less permeable product.

So I would think it's worth doing the "tape down a square of vapor barrier" test to see what kind of results/condensation you get. Although I'm not knowledgeable about how to interpret those results.

Cheers, Wayne
True...I do have adhesive vinyl in two other rooms that have been down for 5 years now and all is well in there. But theres nothing that would mold between the floor and the concrete.

Also in the scenario I want nothing would mold between the DMX and concrete.
 

rb1987

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Is this a good floor to knee wall transition?
 

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