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  1. #1
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    Sep 2009
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    Default insulation for underneath a house

    I recently bought a 1926 spanish bungalow in southern CA. It has new hardwood floors that get very cold in the winter. I put in .9 mm plastic over the dirt, but the floors are still cold. What type of insulation would work underneath this house? I have photos are from an installation of new pipes.
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  2. #2
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    Mar 2009
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    Default Re: insulation for underneath a house

    Hi congratulations on you new home. Fiberglass batt insulation installed in the floor joist cavities is cheapest want R-22 or close to that. Better would be a spray foam but it costs way more.

  3. #3
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    Default Re: insulation for underneath a house

    what r floor joists? Where would the foam be sprayed? Thanks for your time and info timothy...Susan

  4. #4
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    Default Re: insulation for underneath a house

    Hi Susan the floor joists are 2"by10" or 2" by 8" lumber that holds the floor on top of them. They are spaced usually 16" on center and run across from outside wall to wall. Between each board is a space that is about 9 1/4" by 141/2" by the length of the span, length of the joist. In this space, joist bay, is where one installs fiberglass or foam insulation. Consider calling an insulation contractor for a bid. The fiberglass comes in rolls and has a paper facing or just fiberglass. If papered it is on one side and stapled to the joist to keep it from falling down. If no paper then it is secured with wire or mesh to hold it in place. Papered would be the least costly for you to have installed and it is inexpensive.

    Foam usually a separate contractor sprays it into the space the foam expands and sticks to the wood itself so no securing is needed. You have several choices of foam. I would only use open cell foam so if water spilled on the floor it can find a way out of the wood and allow the wood to dry out. Closed cell does not let water transfer threw it.

  5. #5
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    Smile Re: insulation for underneath a house

    Hi Timothy,

    ***. This is really very helpful information. You r amazing..You r so generous with your knowledge. I really appreciate you taking the time to help me. I think I will sue the foam insulation. Seems like it is more appropriate for an outside application. Will send u a photo when it is completed!! Will this foam get in the way of people working under the house, etc? Should I wait until the remodeling is done, as I will be installing a system to let me re-use my water for my plants, etc. Best, Susan
    Last edited by drsusan55; 07-09-2010 at 12:14 PM. Reason: needed to remove misspelling

  6. #6
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    Mar 2009
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    Default Re: insulation for underneath a house

    Susan you are welcome i have learned from seeing mistakes and or damages over the years and to give back some of what i have learned has to be great karma..
    Wait till work done under house to insulate as will not get in way or have to be removed and replaced to allow other work.
    One draw back of foam is that to work in the cavity one must remove it and then respray the area. The fiberglass can be removed and reused easily. So before you make your mind up. Ask the insulation contractors their recommendations and then make an informed decision.

  7. #7
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    Sep 2009
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    LA
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    Default Re: insulation for underneath a house

    Thanks! Will do! Susan

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