How to Insulate the Floors on an Old Pier & Beam

Hire a professional to spray foam to insulate the underside of the floor. Foam insulation doesn't require vapor barriers, has a high R value and is insect and mold resistant. Installers spray wet foam into the spaces between joists. As the foam dries, it expands to fill the spaces completely. Spray foam comes in a variety of forms, some of them environmentally friendly. Consult with your local professional about which is right for your home and climate.

Use foam board insulation. Rigid panels of foam board are placed tightly together on the floor joists under the house, and the seams are taped or caulked. Some jurisdictions require the use of a vapor diffusion retarder on the side facing the floor of the house. Insects don't eat rigid foam, but they do burrow through it. Some manufacturers treat foam board insulation with insecticide to discourage insects.

Staple traditional insulation batts or rolls into the spaces between the floor joists. Install the batts or rolls with the vapor barrier against the floor, and cover the side facing the earth with masonite or thin sheets of plywood to keep birds and rodents out. Rolled insulation comes in standard widths to fit most joist spacing and in high R values suitable for outside insulation.

Install skirting around the house. Skirting prevents drafts from penetrating from underneath the house and is frequently used on mobile homes where a frame holds the plastic or metal material in place. This method doesn't provide the insulating properties of other configurations, but it is effective for a three-season home without insulation in the floor. Skirting options include facades resembling stonework, bead board or brick.