GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon

Community and Q&A

Slab and finished floor questions

Mdubya | Posted in Energy Efficiency and Durability on

GBA community, looking for input.

I currently have an uninsulated slab on grade with vinyl asbestos tile on top. I’d like to go directly over the top with 1/4″ cork underlayment, then radiant mats in thinset, then glue down vinyl sheet flloring.

Wondering if anyone has any experience with something similar. I’m unsure about any moisture issues and the effectiveness of the radiant mats.

Any input would be appreciated.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Steve Knapp CZ 3A Georgia | | #1

    Will your local code allow you to encapsulate the asbestos tile? Does overlayering it with new material count as encapsulation?

  2. GBA Editor
    Martin Holladay | | #2

    M Dubya,
    There are several issues here. In addition to the asbestos issue, there is the thermal performance issue.

    You should tell us your climate zone or geographical location. In general, it's a very bad idea to install in-floor heating over an uninsulated slab. You need a continuous horizontal layer of rigid foam above the slab -- at least an inch, but 2 or 3 inches would be better, depending on your climate zone -- before considering the installation of in-floor heat.

  3. Mdubya | | #3

    As far as I can tell, encapsulating the asbestos is permissible in Washington. Iā€™m going to dig a little deeper and confirm prior to covering.

    Marine Zone 4.

    Slab is 4ā€™ to 8ā€™ below grade and stays a pretty consistent 50-55 degrees year round. Constrained by a couple of factors, main one is the floor comes to the bottom of a set of stairs and if I raise it 1ā€+, I will need to rework the entire set and second floor to stay within code limits. So trying to keep the buildup at a minimum on the floor.

  4. GBA Editor
    Martin Holladay | | #4

    M Dubya,
    If your ceiling height permits, you might consider adding enough rigid foam to your floor to raise the finished floor by the height of one stair riser.

    If the ceiling height is an issue, your plan will work, as long as (a) you don't mind the energy penalty associated with heating an uninsulated floor, and (b) the installation instructions provided by the manufacturers of the cork underlayment, radiant floor mats, and vinyl flooring are consistent with your planned installation.

    I would gather up all these installation instructions (often available online) and read them carefully before proceeding.

  5. Mdubya | | #5

    Thanks, Martin. I am constrained by ceiling height. I will research the instructions and get a better idea of energy efficiency before I proceed.

    Thanks again.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |