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  1. #1
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    Question Basement insulation and vapor barrier

    My 1875 farmhouse was moved back 75 feet from the road and a new basement (concrete block) was constructed. I need to insulate the basement and would like to know the best way to do that. I live in upstate New York, near Buffalo. Several family members have offered suggestions as I was about to install unfaced insulation between the studs. One brother says the insulation needs to be attached to the studs so it doesn't fall down. I thought it would just stay in place because the insulation is a bit wider than the cavity. The studs do not touch the basement walls. They are about 2 inches away from the walls to allow for 6" insulation. Also, I recently watched another home improvement program on TV where the couple installed the vapor barrier against the concrete and then the insulation on top of that. My understanding was that in this climate, the vapor barrier would go towards the warm in winter side. I'm confused! Please help!

  2. #2
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    Default Re: Basement insulation and vapor barrier

    In the basement, the vapor barrier needs to be on the concrete. Where is the moisture? In the concrete. It acts like a giant sponge. When warm air hits your cold concrete, condensation will form. It would have been nice to install the vapor barrier before the walls were built.

    Josh Jaros

  3. #3
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    Default Re: Basement insulation and vapor barrier

    Thank you for the responses. I had originally thought of putting up foam insulation but the cost was higher and it offered less of an R value than fiberglass. Now I've got studs in the way and would probably have to remove some to install foam and especially to install the vapor barrier as jkirk suggests. That's a lot of work!

    Anyone know if it would be alright to install the foam panels directly against the concrete walls, then the fiberglass batts (adding nails to keep them from falling down), and then the vapor barrier on top of that? Do the foam panels come with a vapor barrier? If they were attached directly to the concrete walls with the vapor barrier towards the concrete, would that keep the moisture from entering the area with the fiberglass?

    Just trying to figure out the best way to do this given the existing studs.

  4. #4
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    Default Re: Basement insulation and vapor barrier

    Just throwing 2 cents in this.

    There is plenty of confusion and misconceptions as to the role of the vapor barrier.

    Vapour barriers together with air barriers prevent moisture from escaping into the walls.
    Moisture gets into walls and attics by two paths ...... air infiltration through cracks or gaps and vapour diffusion through the wall materials themselves. Vapor from air infiltration can be 100 to 1 times greater than from diffusion.


    Water vapour manages to filter its way through most building materials ....... which is referred to as diffusion. Although all building materials slow diffusion to a certain extent, only those that almost totally block it are officially classified as vapour barriers and deemed acceptable for new construction standards.

    Permeability is the technical measure of how easily vapour will get through a material and only materials rated as less than 1 perm are considered vapour barriers. Aluminum foil, polyethylene films, aluminum paints, latex vapour barrier paint, vinyl wallpaper, and several coats of oil paint all qualify ....with varing degrees of effectiveness.

    A similar technical measure is given to the permeability of materials as being an air barrier.


    The polyethylene films are the preferred materials for vapour barriers because they come in large sheets, have few joints where air can leak by, and can be efficiently sealed around openings such as windows, doors and electrical boxes.

    If we completely seal a polyethylene sheet on the warm side of the insulation, we call it a combined air/vapor barrier.

    So .... they create an air barrier while also meeting the code requirements for a vapour barrier.

    Keep in mind this is referring to the vapor that exists from the warm moisture laden air within the basement.

    The method of only applying a vapor barrier to the foundation wall would and should never be used up here and in my opinion applies to all cold climates.

    The vapour barrier should be placed on the warm side of the dew point on the coldest day of winter. The objective is to prevent the vapour barrier from getting cold enough to allow condensation on its own surface.

    Having the vapor barrier on the cold side of the insulation will trap moisture inside the wall.

    The method jkirk mentions is used when the foundation walls have a dampness issue ..... not dripping wet.
    With that method there is a continious vapor barrier that is on the warm side preventing moisture from the living space.

    katemap .... you mention this is a new block foundation .
    It's unknown as to the method of damp proofing or waterproofing that was done to the exterior in preventing any chance of moisture or dampness entering from the exterior.

    First thing that comes to mind .... you mentioned this is a new foundation.
    I would recommend waiting till after spring before closing in the foundation walls.

    There is plenty of moisture from the new blocks and mortor that needs to evaporate. If you close these walls in right away you run a good chance of trapping this moisture before it has a chance to acclimate.

    Besides .... it will also give you a chance to see how moist the walls will become from spring thaws.
    Last edited by canuk; 01-25-2009 at 06:53 PM.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
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    Default Re: Basement insulation and vapor barrier

    Quote Originally Posted by katemap View Post
    Thank you for the responses. I had originally thought of putting up foam insulation but the cost was higher and it offered less of an R value than fiberglass. Now I've got studs in the way and would probably have to remove some to install foam and especially to install the vapor barrier as jkirk suggests. That's a lot of work!

    Anyone know if it would be alright to install the foam panels directly against the concrete walls, then the fiberglass batts (adding nails to keep them from falling down), and then the vapor barrier on top of that? Do the foam panels come with a vapor barrier? If they were attached directly to the concrete walls with the vapor barrier towards the concrete, would that keep the moisture from entering the area with the fiberglass?

    Just trying to figure out the best way to do this given the existing studs.


    I'm sure many of folks are tired of this method that I preach.... here goes...



    Extruded Polystyrene that is a vapour barrier can be useful on the inside of the basement wall because here when you do seal the joints, you will have created a useful vapour barrier on the warm in winter side of the insulation.

    There should be absolutely no air space behind the insulation. Even the space behind studs should be filled with insulation

    Attach rigid foam insulation to the foundation walls first completetly covering the walls..... if you use 2 inch you are getting approx. R 9- 10 and the thickness of the foam will provide significant insulation to keep the inner face of the foam fairly warm. This reduces if not eliminates any condensation.

    Use a house wrap tape to cover the seams where they meet at the corners and at the butt joints. Use a can of spray foam along the bottom where it meets the floor to seal this area completely.

    The closed cell rigid foam insulation has a low air and moisture perm. value which means it doesn't pass air and moisture very easily and is an acceptable vapor barrier.

    Then put up the wall framing in front of the foam and apply your wall finish to the studs.

    What you end up with is a continious thermo break behind the wall framing which is far superior to the interupted method of insuluating each stud cavity.

    There is no need to apply any additional vapor barrier with this method.

    Hopefully this makes sense and helps.
    Last edited by canuk; 01-25-2009 at 06:55 PM.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  6. #6
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    Default Re: Basement insulation and vapor barrier

    With all due respect maam, you have started this project the wrong way, and now your are trying to fix it without fixing what you did wrong. I'm afraid that what you really need to do is call a professional carpenter in to help you out. You seem a bit confused as to what you are doing and if you continue on the same path you are going to have some serious mold and rot issues.
    At the very least, have a licensed carpenter come to your house and pay some money for a consultation. It will be well worth your money.

    Josh Jaros

  7. #7
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    Default Re: Basement insulation and vapor barrier

    This is quite a controversial subject. Lots of mixed reviews, lots of diverse experiences.
    I will side with the Building Science Corp. regarding proper basement insulation.

    Please refer to:

    http://www.buildingscience.com/docum..._download/file

    And here's another good article:

    http://www.housingzone.com/proremode...CA6404480.html

  8. #8
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    Default Re: Basement insulation and vapor barrier

    I knew this was a controversial subject when I asked the question and that I'd get some differing opinions. My intention was to get some information before speaking with a local insulation contractor. Thank you all for your 2.

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