Can Insulation Be Placed Under a House on Piers?

Determining the Insulation’s R-Value

• Before you can insulate under a house built on piers, you need to find out the recommended R-value for the region of the country in which you live. Each region has a different climate, the factor that determines how much insulation is required. An insulation’s R-value signifies its resistance to heat flow. Once you know the requirements for your region, obtain paper- or foil-faced insulation to install underneath the house on piers.

Don’t Compress the Insulation

• Ensure the insulation fits the space between joists – the width as well as the depth of the cavity. Many people think if they get an insulation with a higher R-value and then compress it into the space, this will give the area a higher rated R-value. This is incorrect. Once the insulation is compressed, it looses its R-value. Trapped air during the manufacturing process is what gives insulation its R-value, not the individual strands of fiberglass, which have little to no R-value.

Installing the Insulation

• Installing the insulation requires gloves, a long-sleeve shirt and safety glasses, especially when working underneath a house. Start at one end of the joists and install the insulation between the joists. Tuck in any stray edges and smooth the insulation as you go. Avoid compressing or squeezing the insulation. Once you get the feel of installation, it will go quickly.

Moisture Barrier

• Add a moisture barrier over the insulation. While insulation provides resistance to heat flow, it does not provide resistance to moisture or airflow. A moisture barrier, usually made of some form of polyethylene or plastic, retards and diffuses moisture and keeps it away from building materials where it will cause mold, mildew and fungus. Unroll the plastic sheeting and staple it to the joists. Avoid pulling it taut, but ensure it’s flat against the joists. Attach with a staple gun every 12 or 16 inches.