This isn't something that is common in all areas if you are over a certain age - namely, when other folks start having children or living with romantic interests. Seriously. Especially in a small town. And it doesn't work if you don't have friends that are in a similar situation.

The more prudent thing is to make sure that the single person can afford a one-bedroom apartment. Unfortunately, these are often not much cheaper than a two bedroom. Where I lived in the states, a studio wasn't much cheaper either, mostly because they were all in apartment complexes instead of divided up houses.