Installing Foam Board Insulation Over Fiberglass Batts In A Floor

Blown in or loose fill insulation.

Installing foam board insulation over fiberglass batts in a floor.

Fiberglass batts compressed bottom photo pretty much any crawl space with fiberglass batts in the floor above will have the first problem. 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. Insulation blankets batts and rolls spray foam insulation. 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.

Those floor joists extend 25 feet into the interior of my home. 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. 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. Fiberglass insulation is less than half the price of rigid foam insulation when calculated by r value per square foot.

Rigid foam insulation offers a thermal resistance between r 5 and r 8 roughly twice that offered by traditional batt insulation. Batt insulation is that pink fiberglass found in exterior walls attic floors and the crawlspace ceiling. I thought there was insulation in that 8 25 space but there isn t. It is made from fiberglass strands that create a barrier for air flow.

In general the insulation s method of installation can give you an idea of how it compares to other types of 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. 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. Foam board insulation is easy to use and is a great diy way to add some insulation.

Roll or batt insulation. It comes in standard size 4 8 sheets and smaller sizes in many different thicknesses from 1 4 inch to 2 inches. Some types of thicker foam board insulation are available but they may need to be special ordered. 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. It may not happen right away but gravity is patient.