I'm not familure with the Ontario Building code, but it's required everywhere here in the US [using the IRC] (except for certain warm counties in the extreme southern US, and where the cavity has been designed to ventilated to allow for moisture to escape. This would not be desirable in your neck of the woods.)
Keep in mind that the purpose is to prevent moisture-laden air from penetrating the exterior walls and (when it reaches the dew point inside the insulation) condensing into liquid water. (Moisture in air is measured as a pressure, and can (and will) push through any building product to equalize in dryer air. You need to protect not only insulation, but the studs as well. The entire wall needs to be protected.)
You may also run into other minor problems with spray foam, including protecting it from fire with a fire-protective barrier (all codes regulate when & where foam can be used, most either limit the thickness that can be used, and/or require 1/2" gypsum or concrete), and protection from termites (bugs love to burrow through it). The IRC requires a minimum of 6" clearance above ground level.
face=Arial size=2>...</FONT></DIV><FONT face=Arial size=2>> If I use spray
foam inside my garage do I have to install a vapour<BR>> barrier over it like
ordinary insulation ? I'm in Canada, so I have no<BR>> clue if the
Ontario Building code says that you have to install a<BR>> vapour
barrier.<BR>> <BR>> Thank you.<BR>></FONT></BODY></HTML>