Thinking About an ADU? What Homeowners Should Know Before They Build

Accessory dwelling units, often called ADUs, have gone from a niche idea to one of the most requested projects we hear about. Whether it is a detached backyard cottage, a converted garage, or a finished basement apartment, homeowners are drawn to ADUs for a lot of reasons: housing an aging parent, giving a grown child a place of their own, generating rental income, or simply adding flexible space to a property. If you are considering one, here is what to think through before you start drawing up plans.

What Actually Counts as an ADU

An ADU is a secondary, self-contained living space on the same lot as a primary home. That can take several forms. A detached ADU is a standalone structure, sometimes called a backyard cottage or granny flat. An attached ADU shares a wall with the main house, like a bump-out addition with its own entrance. A conversion ADU repurposes existing space, most commonly a garage, basement, or attic. Each type comes with its own cost range, timeline, and complexity, so the right fit depends on your lot, your budget, and what you actually need the space to do.

Zoning and Permitting Come First

Before you fall in love with a floor plan, it pays to understand what your local zoning code actually allows. Many municipalities have loosened ADU rules in recent years to help with housing supply, but restrictions still vary widely from one town to the next. Common things to check include maximum square footage, setback requirements from property lines, parking requirements, height limits, and whether the unit can be rented out short-term or long-term. Utility connections matter too. A detached ADU may need its own water, sewer, and electrical service, which can add meaningfully to the budget depending on how far it sits from existing hookups. Getting clear answers on zoning and permitting early saves you from redesigning later.

Budgeting Realistically

ADU costs vary a lot depending on size, type, and finish level, so it is hard to give a single number that applies everywhere. What we can say is that a garage or basement conversion is typically the most affordable route, since the structure and much of the site work already exist. A detached new-build unit costs more per square foot than an addition to the main house, mainly because it needs its own foundation, roof, and utility connections. Beyond construction itself, budget for permitting fees, utility hookup or upgrade costs, site work if your yard needs grading or access improvements, and a contingency for the unexpected. As with any renovation, it is worth getting a detailed written estimate before committing, so you understand exactly what is and is not included.

Designing for How the Space Will Actually Be Used

The best ADUs are designed around a clear purpose. A unit meant for an aging parent benefits from single-level living, wider doorways, and a curbless shower. A rental unit does better with a separate entrance, sound insulation between it and the main house, and its own mail and utility metering if local rules allow it. A space for a returning adult child might prioritize a small home office nook or extra storage. Even if the current plan is temporary, it is worth designing with resale and long-term flexibility in mind, since a well-built ADU can add real value to a property down the road.

An ADU is a bigger undertaking than a typical remodel, but it does not have to be overwhelming. Starting with a clear picture of local rules, a realistic budget, and an honest sense of how the space will be used puts you in a strong position from day one. A good contractor can walk you through what is feasible on your specific lot before you spend money on design work that will not pencil out.

Ready to start your project? Get a Free Quote