I guess home values would go down, but investment (improvements, remodeling etc.) would go down as well, so the old houses would be pretty shabby when sold. Newly built homes would be either substandard (what the Chinese derogatorily call "tofu quality", where walls aren't really that solid), or available to the wealthy only.
It is surprisingly expensive to build a (brick and mortar) house to 2021 security, energy-saving and quality standards, at least in Central Europe. We have a lot of cheaper housing from the 1960s-1980s, both block of flats and detached houses, but no way would such buildings in their original form be approved today.