Because slabs-on-ground have requirements similar to those pertaining to basement floor slabs, the steps and precautions described for the latter apply here as well. An important difference is the need to establish the finish floor level at a sufficient height above the natural grade so that the finished grade will provide good drainage away from the house (Figure 49). The top of the slab must be at least 150 mm (6 in.) above finished grade.

Remove all debris, stumps and organic matter from the area below the slab and fill voids with compacted granular material to provide a smooth surface free of soft pockets.

Figure 49

Independent concrete floor slab and foundation wall

Install water-resistant rigid insulation around the perimeter of the slab and protect it from physical or ultraviolet damage with parging or a board finish. To resist cracking, reinforce the slab with 9.5 mm (3⁄8 in.) thick steel reinforcing bars spaced 600 mm (24 in.) on centre in both directions. (The steel bars have a metric product designation of 10M.) Alternatively, welded wire mesh can be used that forms a grid of 152 mm (6 in.) squares in which the thickness of the steel is 3.4 mm (0.15 in.). [The metric product designation of this grid is 152 × 152 mm (MW 9.1 × 9.1.)].

Source : Canada Mortgage and Housing Corporation (CMHC)