(AP) — The housing market is tight in many parts of the country. And some people are finding a solution in accessory dwelling units, or ADUs.

Or call them granny flats, in-law units or backyard bungalows.

They're small homes separate from the main house. They can be new structures or converted garages or basements with separate entrances.

Fans of ADUs say they are low-impact, energy-efficient, and can add housing to a neighborhood with less disruption than building new apartment buildings.

Author Sheri Koones has written a book called “Bigger than Tiny, Smaller than Average” that features several examples of ADUs.

She says high ceilings, natural light, built-in-furniture and open floor plans can make them feel more livable than their modest footprints might indicate.