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Community and Q&A

Leveling a basement floor

Vmcmahon | Posted in General Questions on


I’m starting to plan the renovation of my basement. It has a good concrete floor, which is a little uneven and not really level. In addition, it was painted with a glossy epoxy or paint type finish many years ago before I bought it, and it has held up well. Dampness is very minor, over 20 years very minor effervescence… 

My plan is to lay delta fl, 2 inch xps, and subfloor and some type of finished wood /cork flooring

My question is what is the best approach to leveling the floor:

I know I can use SLC. Big project. Have to grind down the existing paint to get a bond. I just did this to an existing basement room that I finished already for a tool shed /mechanical room. Messy job. It was about 12 by 20 and, a tremendous amount of work. But it’s a solid job. 

Do I have other options? Could in level with sand and put a delta FL product over then the xps?

Or do i just lay delta fl, xps and then shim a subfloor? 

Also, from reading in here everyone is very clear about taping joints etc, however also using tapcons for subfloor, which penetrates everything that we just sealed. Is this an issue or am i over thinking? 

Want to do it right, so appreciate the input 


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  1. gusfhb | | #1

    I would just scuff and use leveling compound, you are covering it all anyway

    tapcons are a lot of labor

    I used a 'T' nailer and urethane adhesive/vapor barrier[it is a flooring product] to hold down PT plywood and the hardwood floor and tile over it is good 10 years on. Goes down fast. If the PT was not potato chip like I would have relied on the glue

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Vincent,

    I have used self-leveling concrete on a basement floor and I have tried to shim a subfloor over an uneven slab too. The former is messy and the latter is not easy.

    I remember talking to a residential builder who uses a sub to install self-leveling concrete in his basement remodels. Apparently, it's much more commonly used in commercial remodels, so if the basement is big enough, it can be economical to hire it out. Anyway, something to look into perhaps.

    You can also consider a floating subfloor, screwing two layers of plywood or OSB together instead of fastening one layer to the slab. Many builders prefer this approach for ease of installation and for a stiffer floor.

  3. Expert Member
    Dana Dorsett | | #3

    >"My plan is to lay delta fl, 2 inch xps, and subfloor and some type of finished wood /cork flooring"

    Can I convince you to change out the (environmentally & financially) expensive XPS for EPS instead?

    XPS is blown with a mix of HFC refrigerants, the predominant component of which is HFC134a , with a 100 year global warming potential of ~1400x CO2.

    EPS is blown with hydrocarbons, usually a variant of pentane, with a 100 year GWP of ~7x CO2.

    As the HFCs diffuse out of the XPS over several decades it's performance drops to that of EPS of equal density, or about R8.4 @ 2". While it's is "life time" warranteed to 90% of it's labeled R-value (R9 @ 2"), in 50-70 years you're likely to be able to collect on that warranty if you cared to rip up the floor and test it.

    The majority of the pentane used in EPS escapes the foam at the factory and is recovered (to meet local air pollution regulations), and often burned for process heat yielding water and CO2 (with a 100 year GWP = 1 x CO2) to be vented to the atmosphere. The performance of EPS is stable over many decades.

    So if R10 is an absolute must, bumping to 2.5" EPS will actually deliver that, whereas 2" of XPS absolutely won't, and isn't even warranteed to meet that despite labeling. And R10 EPS is almost always 20-30% cheaper than R10 XPS.


  4. Vmcmahon | | #4

    Hi Folks - Thanks for the responses. All helpful as I plan this project.

    Dana , with regard to the XPS Vs EPS, I certainly have no preference. My goal is to finish the basement as efficiently as I can. XPS appears to be the one that the big box stores push, but If I can get the equivalent in EPS - that works

    thanks - Vincent

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