How to Insulate a Basement Foundation

By insulating your basement foundation, you can reduce heat loss in your home and turn your basement into an additional living space. When you insulate your basement foundation, the most important thing to remember is to install plastic vapor barriers on both sides of the insulation. This helps keep outdoor and indoor moisture from working its way into the insulation. Once insulation gets wet, it loses its ability to insulate.

Things You'll Need

• 4 mm plastic sheeting, enough to completely cover the foundation twice
• Hammer-type staple gun
• 2 inch by 6 inch pressure treated lumber
• 2 inch by 4 inch lumber
• Hammer
• Nails
• Fiberglass batt insulation
• Utility knife
• Drywall
• Drywall screws
• Drywall tape
• Drywall mud

Instructions

1. Put up a moisture barrier. Use the 4 mm plastic sheeting and attach it to the wooden foundation header using a hammer-type staple gun. The plastic should be floor length and extend out 8 to 10 inches from the foundation onto the basement floor. This sheet of plastic keeps outside moisture in the masonry foundation from seeping into the insulation.

2. Install a rim of pressure treated 2 inch by 6 inch lumber around the exterior walls right next to the foundation. This is the base upon which you will build the wall. Lay the lumber on its large flat side on top of the plastic sheeting vapor barrier that is extended from the wall. Make sure the boards are right next to the concrete foundation. Lay them end to end around the entire perimeter. Secure the 2 inch by 6 inch boards to the concrete floor with concrete bolts placed at each end.

3. Frame up the new wall. Use 2 inch by 4 inch lumber of a length equal to the height of your basement, as measured from the floor to the wooden joist on top of the foundation. Build a standard wood frame wall. Space the 2 inch by 4 inch studs 16 inches apart, measured from the center of one stud to the center of the next stud. Place a 2 inch by 4 inch board on its end on top of the pressure treated 2 inch by 6 board installed in Step 2. Secure the top of the 2 inch by 4 inch studs to the wooden joist on top of the foundation with 16 penny nails and then secure the bottom of the studs to the pressure treated 2 inch by 6 inch boards with 16 penny nails. Install the 2 inch by 4 inch studs so the 2 inch side is against the foundation wall.

4. Install fiberglass batt insulation between the 2 inch by 4 inch studs of the new wall. Follow the manufacturer's instructions and specifications to use the correct insulation for your particular climate. The fiberglass batt insulation fits between 2 inch by 4 inch studs installed 16 inches apart. Unroll a batt of insulation and put it in between the 2 inch by 4 inch studs with the foil or paper side facing into the room. Friction keeps it in place between the studs. Cut it to the proper length with a utility knife. Lay the insulation on a flat surface and compress it with a scrap piece of 2 inch by 4 inch lumber at the point where the cut will be made. It will compress down to less than an inch thick and is easily cut.

5. Put up a second 4 mm plastic sheet over the completed and insulated wood frame wall. Staple it to the wooden joist on top of the foundation and to the wood studs of the wall you built in Step 3. This sheet of plastic keeps moisture from working its way from the interior of the house through the drywall into the insulation.

6. Install the drywall. Use standard drywall screws to attach the panels of drywall to the studs. When finished, tape the joints. Apply drywall mud to the taped joints and screw head holes, then sand when dry.

Tips & Warnings

• Wear protective clothing and a mask when working with fiberglass insulation to protect you from the fiberglass particles.

References

• Basement Insulation