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Thread: Rim Joist and Foundation Wall Insulation and Sealing

  1. #1
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    Default Rim Joist and Foundation Wall Insulation and Sealing

    How would you insulate a rim joist on an existing home that currently has next to none? It has 1" styrofoam on the outside of the joist. The insulation goes 5" up the 10" rim joist, leaving a 5" space with just joist, plywood and siding. I don't know how deep the insulation goes.

    There is no insulation on the inside of the joist.

    Pretty easy access to the inside with a 4' crawl space.

    There is rot on the sill plate and rim joist in areas. I will be replacing those.

    How would you insulate and seal once the rotted pieces are replaced?

    Thanks

    Here are a few pictures....
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    Member Yellowknife's Avatar
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    I used a Dow spray foam kit (or equivalent) and sprayed it with two part closed cell foam that is rated for rim joists. The kit looks like two small propane bottles and was available for about $350 from SBS, Lowes or AIH here in Fairbanks. It's tricky to use (nozzles clog pretty quick) and you have to move fast, but it works like a champ and will both insulate and seal.

    Yk

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    Member thewhop2000's Avatar
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    Default you could

    use blueboard and then use metal flashing on top of that to protect it.
    If a dipnetter dips a fish and there is no one around to see/hear it, Did he really dip?

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    Member AKDoug's Avatar
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    Ditto on the "froth pack" two part urethane systems. Much faster than cut and fit with styrofoam. For your situation, spraying from the inside sounds like a much better way to go, then fix the flashing/water issues on the outside this summer.
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    I have considered spray foam, or insulating on the inside with rigid foam.

    I was doing some research today, looking at the cold climate housing research site.

    What if I removed everything on the outside so I had bare rim joist and dug down to the bottom of the foundation. Installed a vapor barrier from the wall sill down. Then install rigid foam over top of the vapor barrier, cover with flashing, and backfill.

    Hopefully that makes sense, I'm not sure if I am using the correct terminology.

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    Here is a little drawing of what I am envisioning.

    The blue in rigid insulation
    The pink is sealant
    The red is vapor barrier
    The gray is the foundation
    The brown is the various structure in the flooring
    The tan is fiberglass insulation

    How would this work? Would the extra effort to do it be worth it? Or should I just repair the rotted pieces, spray the inside, and be done with it....
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    Quote Originally Posted by kgrant View Post
    Or should I just repair the rotted pieces, spray the inside, and be done with it....

    ...you said it.
    "– Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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    first you need to find out why and where the sill plate rotted. After that is done you can do all your insulating from inside your crawl. Ak code on this is r19. you can take r19 and roll it up into your joists. I would also cover your stem wall as well. after you get all insulation done vapor barrier every thing you just did. Now if your stem wall doesn't have a waterproffer on it that needs to be done as well. Just insulating the outside of the stem wall with blue board will not be enough.

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    Do you need some sort of fire protection over foam? i.e. drywall or an intumescent paint coating? Hate to have you insulate then later when you have to sell your home, having to do something unplanned-for.

  10. #10

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    no fire protection needed

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    Member AKDoug's Avatar
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    My foundation is insulated on the outside. I bituthaned the outside of the foundation and extended it up a foot of the wall. I then installed 4" of high density styrofoam on the outside of the foundation and covered it with bituthane. The foam insulation stopped 1" above the rim joist. I then had a custom flashing bent that went 24" down the foudation, 4" over the top of the foam and 12: up the wall. I then sided the house starting at the top of the 4" of foam.

    Anybody in the FBKS area that sells ASC roofing can have the custom flashing bent to your specs in 10'6" lengths in any color that ASC roofing comes in.
    Bunny Boots and Bearcats: Utility Sled Mayhem

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    Thanks for the input. Giving me some different options to consider.

    I believe the main cause of the rot was rhubarb plants that have been growing next to the foundation for 30 years. There is only 10 feet of rot, and it's on the north side of the house, not a bunch of sun to help dry things out.

    I will be taking care of the rot issue.


    Thanks

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    Smile Design Details

    Quote Originally Posted by kgrant View Post
    Thanks for the input. Giving me some different options to consider.

    I believe the main cause of the rot was rhubarb plants that have been growing next to the foundation for 30 years. There is only 10 feet of rot, and it's on the north side of the house, not a bunch of sun to help dry things out.

    I will be taking care of the rot issue.


    Thanks
    Kgrant
    It looks like you are getting some good advice regarding your how to insulate your crawl space exterior stem wall.

    I noticed in one of your photos of the exterior that there was a wood water table installed around the structures perimeter. This was a method frequently incorporated into the structures exterior finish details to keep bulk moisture away from and entering the structures lower perimeter. (Creating a capillary break for the bulk moisture).

    If you cold obtain a copy of – “Builders Guides To Cold Climates” - By Joe Lstiburek I think you will find some helpful information and details. We ideality like to incorporated information such as he has detailed in this book into design details during the design development stage.

    Good Luck.
    Montana

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