An in-law apartment might be an apartment over a garage or a basement suite. Other variations are dwellings attached to a single-family home or a living space completely detached from the home, like a small guest house. Legally, an in-law apartment must have its own entrance, kitchen, bathroom and living space. Common space, such as laundry rooms and living rooms, are usually allowed. The living space is generally anywhere from 300 to 700 square feet.