Here in metro Vancouver, with geographical restrictions of mountains, sea, and the border, we have very little new land left to build new sf detached homes. Home construction consists of tearing down existing houses and rebuilding, or subdividing the lots.

New build condos happen on commercial or industrial land where existing buildings are torn down, and the retail and commerce remains on the first levels, and the condos are built above that.

Allowing offshore buyers to only purchase "new builds" will have little effect on the sf detached market, as the sales model is that developers usually buy  the older homes, tear down and rebuild and then sell to offshore buyers.  Houses as young as 15 years old are subject to tear down, especially in cities like Richmond where favourable zoning keeps allowing bigger and bigger luxury mansions to be built..