Installing Foam Board Insulation Over Fiberglass Batts In A Floor

Do not install insulation with a vapor barrier or facing on top of any other insulation because doing so causes condensation moisture in an area that should remain dry.

Installing foam board insulation over fiberglass batts in a floor.

Fiberglass insulation is less than half the price of rigid foam insulation when calculated by r value per square foot. Fiberglass batts compressed bottom photo pretty much any crawl space with fiberglass batts in the floor above will have the first problem. Blown in or loose fill insulation. The fiberglass batts in the wall above it extend past the bottom of the wall cavity and fit loosely into the cavity of the 2 12 floor joists hiding the fact that there is no insulation in that void.

Though some batts come with a paper or foil facing that can act as a vapor barrier tom silva prefers to use 6 mil polyethylene sheeting cut to fit between the joists and with seams sealed by foil tape to prevent moisture from seeping into insulation. Some types of thicker foam board insulation are available but they may need to be special ordered. For example insulating a 10 square foot wall area to r 15 costs about 3 40 to 4 00 with fiberglass insulation while a comparable r value for rigid foam costs roughly 10. I thought there was insulation in that 8 25 space but there isn t.

Foam board insulation is easy to use and is a great diy way to add some insulation. Install these panels over wall or ceiling cavities including those filled with existing fiberglass batts to boost the r value and improve home comfort and efficiency. Insulation blankets batts and rolls spray foam insulation. Learn more about spray foam.

Rigid foam insulation offers a thermal resistance between r 5 and r 8 roughly twice that offered by traditional batt insulation. It may not happen right away but gravity is patient. Those floor joists extend 25 feet into the interior of my home. It comes in standard size 4 8 sheets and smaller sizes in many different thicknesses from 1 4 inch to 2 inches.

Even though it s the weakest of the three fundamental forces of nature it s plenty strong enough to pull those batts down over time. Roll or batt insulation. Whether using loose fill or batts put the vapor barrier closest to the warm side of your. Here are the installation methods from lowest to highest average r value per inch.

Spray foam can be used almost anywhere in the home including exterior walls ceilings floors attics and basements. This type of insulation typically fiberglass or cellulose insulation can be added over existing insulation provided it s installed.