Finishing a Basement 9 - Adding Insulation

Intro - Moisture Proofing - Subfloor - Lay Out Walls - Frame Walls - Corners, Doors & Ceilings - Electrical - Heating and Plumbing - Insulation - Finishing Walls & Ceilings

By Murray Anderson

Installing insulation in the wall cavities between the studs is mandatory if your finished basement is going to feel warm. You have a couple of choices in the type of insulation you choose. Friction fit fiberglass insulation with an R-value of about R-15 has been used for years. It comes in batts that fit between the studs in your walls and are just held in place by friction. Each batt is about 3 inches thick (which is why you left that extra inch when positioning your stud walls), and because it is fiberglass it can be placed around the wiring and electrical outlets without worrying about fire.

The insulation should be installed from the floor right to the ceiling to ensure you don't end up with any cold air spaces behind your walls that will make your room uncomfortable. The fiberglass is light and easy to work with and can be cut with a straight edge and a utility knife. However, you should wear gloves and a long sleeved shirt when working with the fiberglass batts since the fibers can be quite itchy on your skin.

An alternative insulation for your basement walls is polystyrene foam. This comes in large sheets (24" x 96") and needs to be cut to fit in between the studs (usually a small hand saw is necessary). Polystyrene doesn't provide the same insulation (R-value) as fiberglass but its proponents feel it is better to use in a basement since it is impervious to water and moisture.

Whatever type of insulation you choose, don't neglect to install a vapor barrier over it. A vapor barrier's function is to prevent the movement of warm moist air from the heated interior of the home into the cooler areas in the wall cavity. If the air migration were allowed, the warm air would cool and its moisture would be left behind in the wall cavity where it could cause wood rot as well as mold and mildew.

A vapor barrier is installed on the inside of the insulation closest to the interior surface, in other words, on the warm side of the insulation. The best vapor barrier is a polyethylene plastic sheet (4 or 6 mil) spread over the studs and stapled in place. Overlap any seams by at least one row of studs to make sure no moist air can get into the wall cavity, and for extra safety, tape all the seams.

Intro - Moisture Proofing - Subfloor - Lay Out Walls - Frame Walls - Corners, Doors & Ceilings - Electrical - Heating and Plumbing - Insulation - Finishing Walls & Ceilings

Murray Anderson is an experienced freelance writer with articles published in both the United States and Canada. He has written on a wide range of topics, but specializes in home maintenance and how to's.

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