Crawl Space

In homes or buildings with frame construction over a basement or crawlspace, the floors are usually constructed with framing members called joists, which rest on the foundation sill and support the floor above. The outside ends of these joists, and the space between them, are covered with a band joist (also called rim joist or "header"). This band joist is usually the same size as the floor joists, and runs around the entire perimeter of the building. An uninsulated band joist can account for a significant portion of a building's heat loss, as the only thing separating inside from outside is 5 cm (2 inches) of wood and the siding material covering it. The heat loss through an uninsulated band joist increases when the basement is kept warmer, or contains heating or water heating equipment (as in your situation). Insulating a band joist is an easy way to improve a building's energy efficiency. Unlike finished walls, the band joist is usually readily accessible from the basement (unless the basement has a finished ceiling). The amount of materials needed is minimal due to the relatively small area involved; there are no expensive or specialized tools required; and the skills required are very basic. As a result, the cost of insulating a band joist is relatively low compared with the potential energy savings. Materials: Band joists are usually insulated with either fiberglass batts or rigid foam insulating board. If using fiberglass, use R-12 (minimum) on structures with two-by-four sill plates, and R-20 with 15 cm (six inch) wide sill plates. If the fiberglass has a facing or vapour retarder, be sure that the insulation is installed with the vapour retarder towards the heated space. If using rigid foam board insulation, 7.5 to 12.5 cm (three to five inches) of thickness should be sufficient, depending on the R-value per inch of the material. Foam board insulation materials will generally range from R-3 to R-7 per inch, with the R-value indicated on either the packaging or the insulation board itself. Use enough to achieve a total R-value of 12 to 20. Other than the insulation itself, the only materials needed are some type of fasteners to hold the insulation in place. If using fiberglass, the insulation can be fastened with wire fasteners called "tiger claws". If using foam board, the insulation can be "friction fit" in place if it is measured and cut carefully. Although more expensive than fiberglass, rigid foam board can be a preferred choice due to its ease of installation. Installation Tips: Before installing the insulation, be sure to check any air leakage at the foundation sill joint, and caulk or seal this joint as needed. On the two sides where the floor joists are perpendicular to the band joist, cut the insulation material to a snug fit, and gently push it into place between the floor joists. Be sure that it fits snugly against the band joist, without being compressed (compressing insulation reduces effectiveness). On the sides where the floor joists are parallel to the band joist, cut longer pieces of insulation (sections of 1.2 metres (four feet) or less are easiest to work with). If using fiberglass, the insulation can be held in place with staples (if faced), "tiger claws," thin wire, or fishing line crisscrossed around tacks or nails at one-foot intervals. If using rigid foam board, the insulation can be "friction fit" or glued directly to the band joist for additional holding power. Be sure to fit the insulation snugly around any pipes, wires, or other penetrations through the band joist. Any penetrations should be caulked or otherwise sealed prior to installing the insulation. If any water or heating pipes run along the band joist area, be sure that the insulation is fitted between the band joist and pipes, with the pipes on the warm side of the insulation. If rigid foam board is used, caulking can be applied to the joint between the foam board and adjacent wood or concrete after the insulation is in place, to obtain the desired air seal. Cost/Savings Information: In most cases, the cost of insulating a band joist is minimal. The primary factors affecting the potential savings are the average temperature in the basement and typical winter outdoor temperatures. The greater the difference between warm basement temperatures and cold outdoor temperatures, the greater the heat loss through the band joist, and the greater the potential savings.