Accessory dwelling units are known by many names: in-law suites, guest houses, or basement conversions, among others. What all ADUS have in common is that they’re a separate living space typically added to a single-family residential lot, and they’re having a moment.

If you’re thinking about an ADU, here’s what to consider before you commit.

1 Why ADUS are increasingly

popular In recent years, several cities and some states have passed laws making it easier for homeowners to create ADUS, in part to address housing shortages and rising costs that have led to an affordability crisis in many communities. ADUS are seen as a relatively inexpensive way to increase the supply of more affordable housing without drastically changing the character of residential neighborhoods.

Demand is also being fueled by the aging of the U.S. population, says Rodney Harrell, vice president of family, home and community for AARP, which publishes a guide called “The ABCS of ADUS.” People are considering adding space for older family members or caretakers.

2 Costs — and acceptance — vary widely Converting existing space, such as a garage, attic or basement into an ADU can cost about $50,000, while a new detached ADU often exceeds $150,000, Harrell says. And depending on where you live, getting permits to create your ADU can be a relative breeze, an extended fight or flat-out impossible.

Most U.S. cities either do not allow ADUS or have strict regulations that inhibit their development, says Kol Peterson, an ADU consultant and the author of “Backdoor Revolution: The Definitive Guide to ADU Development.” Even where ADUS are legal, cities may require zoning exceptions called variances, demand expensive upgrades or impose fees that can add substantially to the cost, Peterson says.

3 How ADUS are like

swimming pools As with any home improvement project, there’s no guarantee you’ll get your money back from an ADU when you’re ready to sell the home, says real estate appraiser Jody Bishop, president of trade group the Appraisal Institute.

ADUS have a lot in common with swimming pools, he adds. In-ground pools are an accepted and even expected feature in some neighborhoods, so you may recoup at least some of the cost of building one when you sell your home. In other areas, pools are uncommon and could detract from a home’s value if buyers are concerned about maintenance hassles or drowning risks, Bishop says.