Floor Framing at Projections

Floor joists sometimes project beyond the foundation or framed wall to provide support for a bay window or additional floor space in the upper rooms. The cantilevered portion of the floor framing should not exceed 400 mm (16 in.) for 38 × 184 mm (2 × 8 in.) joists and 600 mm (24 in.) for larger joists (Figure 65). In either case, this projection should not carry loads from additional floors. If the cantilevered floor joists are to carry additional loads, they must be specifically designed for the appropriate loads according to accepted engineering practice. Extend the subflooring flush with the outer framing members.

Install insulation carefully on top of the soffit finish under the cantilevered floor and up the inside face of the joist header and end joists. Consider using spray foam insulation. Place the vapour barrier on the warm side of the insulation and install an air barrier to prevent air leakage through the cantilevered floor assembly.

Figure 65

Source : Canada Mortgage and Housing Corporation (CMHC)