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  1. #1
    Join Date
    Sep 2008
    Location
    Camano Island, WA
    Posts
    1

    Default Cutting Styrofoam Sheets

    I want to use sheets of 1" thick styrofoam to insulate the underside of my shop roof. The sheets will need to be cut to match the width of the rafters, wherein lies my question. What is the best way to trim the styrofoam to proper size and minimize the waste and messiness of cutting with a utility knife?

  2. #2
    Join Date
    Aug 2007
    Posts
    612

    Default Re: Cutting Styrofoam Sheets

    Table Saw?

    Watch your hands!

  3. #3
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,836

    Default Re: Cutting Styrofoam Sheets

    Make a bow saw with a bow bigger than the width you want to cut and instead of a saw blade use a thin guitar string.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  4. #4
    Join Date
    Jan 2008
    Posts
    731

    Default Re: Cutting Styrofoam Sheets

    an electric carving knife you know the ones with two opposing serrated blades works really well.

    slapping foam board against the bottom of the roof deck between supports might not be a good idea though.

  5. #5
    Join Date
    Dec 2008
    Posts
    2

    Default Re: Cutting Styrofoam Sheets

    I would like to venture a guess on why the foam on plywood is not a good idea. If you have a leak in the roof, the foam may hide it until it is a major repair of replacing sections of sheeting.

    It may also allow the roof to heat up in the summer as the air can't cool the summer sun. This could shorten the fiberglass or asphalt shingles.

    I doubt if there would be a vapor problem from the living area as this would happen if you laid it down on the attic floor.

  6. #6
    Join Date
    Aug 2008
    Posts
    54

    Default Re: Cutting Styrofoam Sheets

    I've never tried it, but there was a hot wire knife used by model railroaders to slice styrofoam laid in scenery that is supposed to work well. I'm not sure who carries them, but you might ask your local hobby dealer.

  7. #7
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,661

    Default Re: Cutting Styrofoam Sheets

    Some soldering gun kits come with a "hot knife" attachment that can be used to cut foam board. You may also be able to score the foam board with a utility knife and snap the board, rather than trying to cut all the way through which will be messy.

    In most cases, you want to provide ventilation to the underside of the roof (ventilation to the outside). This will help to prevent moisture damage -- and for those readers in colder climates, will help prevent ice dams in the wintertime.

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