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Best way to insulate an old attic?

BGrimsleyII | Posted in General Questions on

I am the owner of a 100-year-old two-story house in the 5A climate zone. The house has a full-height attic space, which is currently uninsulated. The attic has actual floor boards in place over the joists, which could be removed, but would be a lot of work. Right now we just use the space as storage, and don’t plan to convert it to living space. During the winter i run into huge icicle and ice dam issues. My question is, would it be beneficial to me to insulate the parts of the roof that are accessible(id say 70% is not covered)? Or should i remove the floor board and insulate the second floor ceiling?

Any other suggestions would be appreciated as well.

I consider my self pretty handy, I’m just not sure the best course of action. Ive read both ways on other forums and DIY sites.

Thanks for the help.

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  1. GBA Editor
    Martin Holladay | | #1

    The best approach in your situation is to insulate the attic floor by blowing cellulose into the joist spaces under the floorboards. You may have to remove a few floorboards or drill a few holes to gain access to these joist spaces, but that work isn't difficult.

    For more information, see Borrowing a Cellulose Blower From a Big Box Store.

    It's probable that your floor joists don't provide enough depth to give you the R-value you want. If that's the case, you'll need to install new floor joists, perpendicular to the existing floor joists, in order to increase the depth of the insulation layer. If you go this route, you can temporarily remove the floorboards and reinstall them above the new joists, or you can leave the floorboards in place and install new plywood.

  2. BGrimsleyII | | #2

    Martin, I apprecaite the quick response and information. The only caviot i forgot to mention is that my house still has some old knob and tube wiring in place that runs under the floor boards. Ive been told and read that those two dont mix well. Would this change my attack strategy or does new insulation have some direct heat resistive nature to it? Thanks again.

  3. GBA Editor
    Martin Holladay | | #3

    You'll find a discussion of knob-and-tube wiring in the comments section of this article: Borrowing a Cellulose Blower From a Big Box Store.

    While most building codes forbid insulation to be blown around knob-and-tube wiring, there is very little evidence that the practice increases the risk of house fires.

    That said, most homeowners don't want to be on the bleeding edge of retrofit practices (especially when it comes to fire safety). The standard advice for someone in your situation is to hire an electrician to upgrade the wiring in your attic.

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