I agree with Beth for the first cut. But, you included "single-family" in your description. So, you may want to look at household type (HHT). The values 1,2, and 3 correspond to what the Census Bureau usually calls a "family". If you want to include unmarried couples, you could look at the PARTNER variable as well. A lot depends on your definition of "single-family". Also, are you interested in single-unit structures vs condo or coop apartments? In that case, the BLD variable can also be helpful.