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Community and Q&A

Basement Ceiling

nynick | Posted in Energy Efficiency and Durability on

Z5, Coastal CT
During a total renovation of our old home we’re planning on finishing and conditioning the basement. Current plans are Dri-cor on the floor, with 2×4 walls 1″ from the foundation walls along with 2″ of CC SPF. We’ll have a mechanical room with an air handler, well (yes, well!), HP DHW, well pump and pressure tank, along with other bits and pieces. We’ll also have a separate storage room. The rest will be  playroom type space with TV, stereo, bar etc. It’s a pretty big basement.

We’ll be keeping the old wood floors on the first floor and installing some new ones. My builder wants/strongly suggested we insulate the basement ceiling or else the (new?) wood floors may or will warp and “cup” in the future, I guess from humidity? The basement is currently pretty dry and I assume will get a lot less humid after the work is completed. I could always buy a dehumidifier.

I’ve read here that insulating the basement ceiling isn’t the right thing to do, but now he’s got me thinking…and maybe it would be good for sound proofing.

Any suggestions? Once that ceiling is up it will be impossible to insulate.



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  1. Expert Member
    BILL WICHERS | | #1

    Insulating the basement ceiling won't do anything for humidity control. It will do a little for sound control, but not as much as you might think. If you want good sound control, hang the ceiling drywall from resilient channel and use a double layer of 5/8" drywall which together WILL make a big difference in sound transmission.

    It's usually recommended to use a moisture tolerant flooring in a basement, which rules out carpet and also wood in most cases. Some of the engineered wood floors might be OK though.

    I would use rigid foam (polyiso) against the walls and not spray foam. Rigid foam is cheaper and greener. You are supposed to have R15 in your climate zone, which is 2.5" polyiso (which gives you R16). I'd put the polyiso directly againt the masonry and then frame right over that -- there is no need to leave a gap. You can save some space by framing "on the flat" to form a wall only 1.5" deep, which is still enough for electrical if you use 4" square boxes and mud rings.


  2. Expert Member


    Once something is incorporated into the conditioned area of house it needs to be maintained close to the same temperature and humidity as all the other areas. That's what I'd concentrate on, not trying to buffer the areas above from the ambient conditions in the basement.

    1. nynick | | #3

      Right, thanks gents. I fully intend to condition the basement. It'll be easy to do since we'll be running ducts to supply conditioned air to the first floor anyway. I was going to use "luxury" vinyl plank flooring on the basement floor over the Dri-cor.

      The builder is so concerned he's suggesting engineered hardwood flooring for the first floor instead of solid planks or oak. Not a fan of that stuff for my main home.

      1. Expert Member
        MALCOLM TAYLOR | | #4


        As Bill said, the cupping comes entirely from differences in humidity in the spaces. Eliminate that and you won't have a problem.

      2. Expert Member
        BILL WICHERS | | #5

        If you condition the basement, you should have LESS issues with the first floor. If you use polyiso against the walls, that will cut down on moisture getting in that way. If you don't have poly under your basement slab, you can put an epoxy coating on top of the slab prior to putting down the dricore tiles, the epoxy will help to form a durable vapor barrier. Epoxy is more durable than some of the floor paints, but if you want to save some money, some floor paints can also act as a vapor barrier. I'm pretty sure the Drylok people make such a floor paint. Once you've sealed up the basement, you'll have less moisture issues than you started with, which should make the choice of flooring material for the first floor a non-issue.


        1. DC_Contrarian_ | | #6

          I've been looking into the issue of vapor barrier paint for basements (see this thread, ). It's complicated because most paint manufacturers don't provide permeance ratings on the label. What I've learned is that many waterproof coatings are vapor-open. In particular, all of the Drylok products I've looked at are vapor-open. Of the two-part epoxies, some are vapor barriers and some are not. Anything rated for exterior use on wood is probably not a vapor barrier, because if it was it would tend to bubble as moisture is released from the wood. It seems the best bet is an interior primer that is designated as a vapor barrier and recommended for use on concrete, covered with an interior paint if exposed.

  3. DC_Contrarian_ | | #7

    I'm very skeptical of Dri-cor. I think it's expensive for what it does, and their marketing is deliberately misleading about what you should be trying to accomplish in a basement.

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