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  1. #1
    Join Date
    Mar 2012
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    Default Vapor Barrier and Insulation for concrete floor

    I live in Upstate NY. I have a breezway that connects my kitchen and garage. It has a concrete floor. I want to convert this space and use it year round. I want to put a floor over the top of the concrete but I need to first isolate the moisture in the concrete. I'm afraid if I just lay a vapor barrier down over the concrete, I will end up with mold on the underside of the vapor barrier which will eventually find it's way into the space. Any suggestions? Also, what is the best (highest R value) to use?

  2. #2
    Join Date
    Aug 2007
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    4,045

    Default Re: Vapor Barrier and Insulation for concrete floor

    Quote Originally Posted by eshannon View Post
    I live in Upstate NY. I have a breezway that connects my kitchen and garage. It has a concrete floor. I want to convert this space and use it year round. I want to put a floor over the top of the concrete but I need to first isolate the moisture in the concrete. I'm afraid if I just lay a vapor barrier down over the concrete, I will end up with mold on the underside of the vapor barrier which will eventually find it's way into the space. Any suggestions? Also, what is the best (highest R value) to use?
    There isn't really a concern , per se , with mold forming between the concrete slab and the vapour barrier covering the slab. Mold lives on organic material ( like wood and paper for example ) --the concrete is too acidic and vapour barriers ( like 6 mil poly ) are generally synthetic materials.

    Where you may encounter issues is between the room side of the vapour barrier and the floor covering. Depending on what your planned floor covering will be and the method of installation will determine what issues you may encounter.

    For example -- if you decide on laying hardwood chances are you will have a plywood substrate laid ontop of the vapour barrier followed by the hardwood planks laid directly over the plywood. With a slab on grade situation such as yours there will be two things that can happen here:

    1) within a year you may find the hardwood cupping.
    2) mold forming on the plywood substrate and underside of the harwood planks.

    Reason being, the floor temperature ( being a slab on grade ) will be colder than the air temperature within the space. Just like condensation forming on windows so too will condensation form under the floor creating the issues mentioned above.

    Aside from comfort , you need to raise the temperature of the floor to raise the dew point and preventing any condesation moisture issues.
    Two things can be done to raise the temperature of the floor --- 1) insulation --- 2) heat the floor.

    As for insulating the floor , you can go with the old sleepers and inslation method -- or lay extruded rigid foam instead of sleepers --- or use a product called Dricore --- or a dimpled product from Superseal.


    If you are choosing tile the condesation issue isn't so much of an issue as long as the substrate isn't wood.
    If the tile will be laid on the slab itself I would recommend a membrane from Schulter or Superseal with an electric in floor heat system. However, you want to ensure there isn't an issue with excess moisture wicking from the ground into the slab otherwise it may compromise the mortar bond to the slab.

    One thing I would highly recommend is to insulate the exterior perimeter of the slab .


    Hopefully this makes sense and helps.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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