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Community and Q&A

Finished Basement New Construction

bongo30 | Posted in General Questions on

What is the proper way to finish a basement in new construction? Our basement slab has 15-mil poly and 3” rigid mineral wool under it. Our basement walls have R-10 insulation installed on the exterior on top of the waterproofing. So far I had seen suggestions on how to finish the basements in retrofits and existing homes (poly, taped rigid foam on the interior, etc followed by studs). But what about new construction? Can we put the framing/studs directly on concrete slab? Do we need rigid foam or any other membranes? We are framing out a laundry room and a bathroom in the basement so trying to do it the right way since it’s a new construction. Thank you!

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  1. Expert Member
    PETER Engle | | #1

    Your existing insulation is pretty good, especially the 3" of rigid under the slab. The R-10 exterior on the foundation walls might be a bit low, depending on your climate zone. If you tell us where you are, it would be helpful.

    Once the slab and walls dry out, finishing should be pretty straightforward. Note that it can take a year or so for the slab to fully cure and dry and it's best to not install any vapor-impermeable materials on or over the slab until it's fully dry. Beyond that, you should be safe using any form of insulation (fluffy or foam) on the walls and you shouldn't need anything on the floors. I would still steer away from fluffy insulation because basements always get wet sometime and foam is more forgiving of occasional water exposure. If it were my basement, I would probably add an inch or two of rigid foam to the walls, then build the stud walls inside of that. Recycled foam would be great, and inexpensive. Type doesn't matter, though polyiso foam is less water tolerant than the others. I often specify metal studs for basements - again durable with occasional wetting and not mold food. I also generally specify some form of mold- and moisture-tolerant drywall. The various big drywall manufacturers all have some variation of either treated paper faced drywall or smooth fiberglass faced drywall.

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