Insulating Your Attic Floor

According to the U.S. Department of Energy, adding insulation to the attic is one of the most cost-effective ways to help cut heating and cooling costs. Insulating your attic floor is a straight-forward, low-impact step to keep heat in, and prevent damaging ice dams along your exterior roof line. Although the current set of recommendations call for insulating anywhere from R-38 to as high as R-60, retrofitting an older home is a different story and one must be sensible. We recently insulated our attic, for example, allowed us to use R-30 - the maximum our existing joist space would allow without raising the floor. With an old house, we have to let go of the "all or nothing" mentality, something is better than nothing when it comes to insulation. We immediately noticed warmer rooms below and a definite reduction in ice daming along the roofline, so we consider the project a success even though it didn't meet current "standards."

Here's our advice for adding insulation to your attic floor:

1. If you have original floor boards, do your best to carefully remove and save them for reuse, as well as any original iron nails. Use various hand tools including a flat bar, cat's paw, hammer and nail puller to lift the nail a little at a time, working ahead of the nail, so that the force of the bar is spread out and you don't damage the wood.

2. Measure the depth of your floor joist space, and buy batts or rolls of fiberglass that will fit snuggly, with highest R-factor available. You can test for depth before pulling up floor boards by drilling some ¼ inch holes and using a stiff piece of wire to check your depth.

3. If old insulation exists, inspect it carefully before simply adding to it. Years of improper ventilation could have matted it down, prior efforts at working on wiring or other systems could have caused coverage to be inconsistent, and nesting pests might have ruined entire areas. It may make sense to clean out cavities and install new, fluffy insulation. Always wear a respirator 1/2 mask with H.E.P.A. (high efficiency particulate air) filtration cartridges, and cover all bare skin when working with any insulation materials as even new stuff is nasty. Caution: some forms of older vermiculite insulation are known to contain asbestos.

4. This is a good opportunity to update any wiring or services while everything is open and visible. You never want to insulate over wiring that is frayed or has worn-out coverings. If the wiring runs through joists perpendicularly, cut insulation to fit around it.

5. If no insulation exists, or you are removing old insulation, you can opt to use a vapor barrier facing the living space (heat source). The paint covering our living spaces is also considered an excellent vapor barrier. Always use unfaced fiber glass with no vapor barrier to layer on existing blanket or loose-fill insulation.

6. Insulation must retain its loft to work, so you can't smush it down, or cram it into a space. Use a utility knife to custom-fit pieces. Be careful when installing insulation that you do not block any vents along the eaves.

7. If you have no floor and are planning to put down plywood, do not use any vapor barrier insulation, as plywood has some vapor barrier qualities and you risk trapping moisture.

Project Note: Any time you insulate you must also ventilate because trapping heat during cold weather creates dew point (condensation) and this moisture must be allowed to ventilate out of the building.