Concrete Block Foundation Walls

Concrete blocks are available in various sizes and shapes, but the most common ones are modular sizes 200 mm (8 in.) high, 400 mm (16 in.) long, and 150, 200, 250 or 300 mm (6, 8, 10 or 12 in.) wide. The actual size is 9.5 mm (3⁄8 in.) less than the modular size to allow for the mortar joint.

Block courses (rows) start at the footings and are laid up with 9.5 to 12 mm (3⁄8 to 1⁄2 in.) mortar joints. No joint should exceed 20 mm (3⁄4 in.). Tool all joints smooth to resist water seepage. Use full bed and head joints in the bottom course. Succeeding courses may be laid with mortar applied to the contact surfaces of the block. For a higher wall, it may be necessary to add steel reinforcement to a concrete block foundation wall. Pilasters are column-like projections that normally protrude into the basement space. They are sometimes required to strengthen a wall or support a beam, in which case they need to be placed to a set height, usually lower than the top of the foundation.

Use special concrete blocks, such as universal, pier or sash blocks to frame the sides of openings for basement doors and windows. Sash blocks (Figure 44) have a keyed face or recess into which the frames are connected, thus providing rigidity and helping to control air infiltration. Use proper sill and lintel details to achieve the same effect.

Figure 44

Concrete blocks for foundation construction

Source : Canada Mortgage and Housing Corporation (CMHC)