Insulation Of Floors

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Floors over unheated crawl spaces or over heated or unheated garages should be insulated.

Where there is no finished ceiling on the underside of the floor, some material must be added to support the insulation. For friction-fit type batts or for rigid insulation (Fig. 120), wire lath or "chicken wire" tacked to the bottom of the joists may be the most economical method. For loose fill-type insulation (Fig. 121), the support must be provided by a material which is solid (to prevent the insulation from falling through) but permeable (to avoid trapping water vapour which

Floor over unheated crawl space insulated with friction-fit batts.

5/8" (15.5 mm) T and C plywood subfloor

R-31 (RSI 5.46) friction fit insulation

2" x 8" (38 x 184 mm) joists at 16" (400 mm) on centre wire lath (or other suitable material)

Note: Joist sizing is for example only

Effective Thermal Resistance R-243 (RSI 4.28)

5/8" (15.5 mm) T and C plywood subfloor

R-31 (RSI 5.46) friction fit insulation

2" x 8" (38 x 184 mm) joists at 16" (400 mm) on centre wire lath (or other suitable material)

Note: Joist sizing is for example only

Effective Thermal Resistance R-243 (RSI 4.28)

Floor over unheated crawl space insulated with loose-fill insulation.

carpet fibrous underlay

2" x 8" (38 x 184 mm) joists at 16" (400 mm) on centre

R-31 (RSI 5.46) glass fibre loose-fill insulation

7/i6" (11 mm) insulating fibreboard sheathing

Note: Joist sizing is for example only m)

Effective Thermal resistance R-27 (RS! 4-9Û

happens to penetrate the vapour barrier).

The vapour barrier must be installed on the upper or warm side of the insulation. No additional vapour barrier need be installed where a plywood subfloor with tight-fitting or sealed joints is used, because it is generally a good air barrier and a very good vapour barrier.

The insulation must be tightly fitted around cross bridging or blocking between joists. This requires particular care with batt and rigid insulation. It is also important not to omit insulation in small spaces such as between blocked double joists or between a wall and the first joist. In such cases, the insulation should be cut slightly oversize and carefully installed to avoid bunching and excessive compression.

When the insulation is installed only at the bottom of the joist space, the area at the ends of the joist must be carefully considered. The area of the joist header is, in effect, a wall and should be insulated accordingly. Also a well-sealed air barrier must be provided around the perimeter and beneath the insulation to minimize the possibility of cold air leaking into the joist space and "short-circuiting" the insulation.

Insulating a floor over unheated space reduces the heat loss through it, but may not prevent it from feeling cold. Filling the floor cavity with a sprayed-in-place foam type or blown-in-place blanket type insulation is an effective alternative to providing radiant floor heating. The use of carpeting or rugs may also improve the comfort of floors over unheated spaces.

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