They go by different names depending on where you live. Accessory apartment, in-law suite, granny flat, secondary suite, ohana unit in Hawaii, casita in the Southwest. Here in the Houston area, most buyers and sellers I work with just call it an ADU, guest house, or sometimes a casita, and want to know what it actually means for their property.
An accessory dwelling unit is a second living space on a single-family lot that functions independently from the main house. The U.S. Department of Housing and Urban Development defines it as a separate unit with its own kitchen and bathroom facilities, and it can be either attached to the primary residence or built as a standalone structure. I've seen ADUs come up more and more across The Woodlands, Conroe, Cypress, and Katy over the past few years, often for reasons that go well beyond the traditional in-law suite. Some homeowners want space for aging parents. Others want a place for an adult child who is saving toward their own home. A growing number are looking at an ADU as a way to generate rental income on a property they already own.
Below I'll walk through what counts as an ADU, the different types you'll run into, how owners are using them, and the things you need to think through before adding one to your property.
What Counts as an ADU?
A true ADU offers both proximity to the main house and genuine privacy for whoever is living in it. At minimum, you're looking at a separate entrance, a bedroom or sleeping area, and a full bathroom. Many also include a kitchenette or full kitchen along with a living area, which is what separates a real ADU from a converted bonus room.
What Types of ADUs Are There?
Attached ADUs connect to the main house or sit within the existing structure while still functioning as an independent living space, usually with a separate entrance on the side or back of the home. These tend to require less square footage and cost less to build than a detached unit.
Detached ADUs are standalone structures built on the same lot as the primary residence. They offer the most privacy of the three types, which is part of why they tend to work best as rental units.
Interior ADUs are carved out of existing space inside the main house, often a basement or attic that's been converted into a separate living area. These can still include a private entrance depending on the layout of the home.
How Are Homeowners Using Their ADUs?
An ADU is a versatile feature that can serve many purposes. Here are some uses to consider:
Home office | Flex Space. For anyone working from home or running a small business, an ADU offers a dedicated, separate space without competing for room inside the main house. Additional uses include hobby rooms, home gyms, and creator studios.
Guest quarters. Out-of-town family or friends get their own space, and everyone keeps a little privacy during the visit.
Multigenerational living. With homeownership costs where they are, more families across Northwest Houston are choosing to live together while keeping some independence. An ADU lets adult children build savings while living on the property, and it gives aging parents a comfortable, practical place to stay close to family.
Rental income. A properly equipped ADU functions as a full apartment, which makes it a strong option for long-term tenants or short-term platforms like Airbnb and VRBO. For many owners, the rental income helps offset the cost of building the unit or contributes toward the mortgage itself.
What Should You Consider Before Building One?
Local building codes and zoning laws. This is where I always tell clients to start. Zoning rules vary by city and county, and Harris, Montgomery, Fort Bend, and Waller counties each handle ADUs a little differently. Your local zoning office can tell you what's allowed based on your lot and block number, and your HOA may have its own restrictions on top of that. If income generation is the goal, check on permitting and inspection requirements for rental compliance before you get too far into planning.
Purpose. Who is going to use the space changes what you build. Aging parents may need wider doorways, ramps, or grab bars. A home office has a completely different layout priority. Get clear on the purpose first, and the design decisions get a lot easier.
Utilities and infrastructure. Most ADUs run off the same gas, water, and electrical systems as the main house, so it's worth confirming those systems can handle the added load before construction starts.
Budget and financing. ADUs are usually smaller projects than a full home addition, but they're still a real financial commitment. Home equity loans, construction financing, and cash-out refinancing are all options worth discussing with a lender early in the process.
The Bottom Line
An ADU adds flexibility to a property in a way that few other improvements can match, whether you're planning for family, income, or simply more usable space. If you're considering adding one to your home in The Woodlands, Conroe, Cypress, Katy, or anywhere across Northwest Houston, I'm happy to talk through how it could affect your property's value and what local rules apply to your specific lot.
Jason Gracey, Great Houston Properties — (832) 541-5060 | greathoustonproperties.com
