(2)  Joints required in Sentence (1) shall be designed to resist moisture penetration and shall be keyed to prevent relative displacement of the wall portions adjacent to the joint.

Article 9.15.4.9 Ontario Regulation 332/12 Building Code,   Information published by oncodes.ca for educational purposes only.

Cracking in concrete slabs and walls can be minimized by using steel reinforcing rods or control joints (Figure 42) formed by nailing bevelled wood strips to the inside of both interior and exterior wall forms. Their purpose is to create a weakness in the wall that will predetermine the location of shrinkage cracks.

Figure 42

Source : Canada Mortgage and Housing Corporation (CMHC)