Foundations for garages are usually concrete or masonry. Concrete slab-on-ground or preserved wood foundations are also options. The minimum depth below grade for a garage foundation attached to a house should not be less than that shown in Table 3 (p. 264).
If fill is required below the floor, use compacted granular material to avoid settlement after the floor is placed and loads applied. The concrete floor should be at least 75 mm (3 in.) thick. Provide an airtight curb or partition at least 50 mm (2 in.) high at the edges of the slab adjacent to interior space, and slope the garage floor to the outdoors.
Place and cure concrete garage floors the same way as basement floor slabs. Provide control joints so that the concrete segments are similar in size. For a single car garage, one control joint dividing the floor into two roughly square segments should be sufficient.
The foundation walls should not be less than 150 mm (6 in.) thick and should extend at least 150 mm (6 in.) above grade.
Sill plates should be anchored to the foundation wall or slab with anchor bolts spaced not more than 2.4 m (8 ft.) apart and with at least two bolts in each sill piece. Extra anchors may be required at the side of the main door and in areas with high earthquake or wind exposure.
Source : Canada Mortgage and Housing Corporation (CMHC)