Garage-to-ADU Living
Garage-to-ADU Conversion
Converting a garage into an accessory dwelling unit is one of the most efficient ways to add an independent home. We handle the design, permitting, and construction required to make it legal, comfortable, and lasting.
What Garage-to-ADU Conversion Includes
- Feasibility and zoning review
- Kitchen, bath, and private entrance
- Utilities and life-safety planning
- Insulation, conditioning, and finishes
- Permitting and legal occupancy
- Rental and multigenerational layouts
Every element is coordinated as one design-build project—see how the approach comes together in our related collection.
Our Design-Build Process
Because one accountable team handles both design and construction, your garage-to-adu conversion follows a clear path: consultation, existing-condition review and 3D scanning, design and scope development, budget alignment, permitting, construction coordination, and a final walkthrough. Learn more about our team.
What makes a garage actually convertible
Garages look like the cheap path to an ADU because the shell already exists. Whether that holds true comes down to five things we check before anyone draws a plan.
- The slab: most garage slabs are uninsulated and poured without a vapor barrier, which matters once the space is heated and occupied
- Ceiling height after the floor is built up and the roof is insulated, which is often tighter than people expect
- Foundation depth, since garage foundations are sometimes shallower than those under living space
- Whether the garage is attached or detached, which changes the fire separation and code path
- Wastewater, because on an unsewered lot Title 5 counts the new bedrooms against your existing septic capacity
You can get a first read on the zoning and septic side in about a minute with our ADU feasibility checker.
The honest tradeoffs
A garage conversion usually costs less per square foot than a detached build, but less is not the same as cheap, and there is a real cost that never shows up on an estimate.
You lose the garage. In New England that means losing winter parking and the storage that was absorbing everything the house could not hold, and it can affect resale for some buyers. That is worth deciding deliberately rather than discovering later.
On the build side, the savings come from having a foundation, walls, and roof already in place. The spending goes into slab insulation and moisture control, a conditioned envelope, egress and daylight, and bringing utilities to a space that was never designed to be occupied. Where the existing structure is sound, it remains one of the most cost-effective routes to a legal dwelling unit.
Service Areas
Capstone provides garage-to-adu conversion throughout Greater Boston, MetroWest, and Norfolk County, including Boston, Foxborough, Newton, Wellesley, Weston, Needham, Brookline, Lexington, Cambridge, Belmont, Milton, Hingham, Walpole, Sharon, Mansfield, Wrentham, Norfolk, Plainville, and the surrounding communities. See all areas we serve.
Related services
All services →Frequently asked questions
Is a garage-to-ADU conversion allowed?
It depends on the property and local requirements. We assess feasibility and permitting before design so expectations are grounded.
What does a garage ADU include?
A self-contained unit—kitchen, bathroom, private entrance—built to the standards of independent living.
How is this different from a garage conversion?
A conversion adds living space to your home; a garage-to-ADU creates a separate, legal dwelling with its own systems.
Do we lose the garage permanently?
In practice yes, once it is converted to legal living space. It is worth weighing the loss of parking and storage, and any resale impact, before committing. Some homeowners pair the conversion with a carport or a detached storage structure.
Is the existing slab a problem?
Often it needs work. Most garage slabs were poured without insulation or a vapor barrier, which is acceptable for a car and not for a heated, occupied room. We assess the slab early because the remedy affects both ceiling height and budget.
Does a garage conversion count as an ADU?
It does if it becomes a self-contained dwelling with its own kitchen, bathroom, sleeping area, and entrance. If it becomes additional living space connected to the main house, that is a garage conversion rather than an ADU, and the requirements differ.
Planning a garage-to-adu conversion project?
Book a private design-build consultation. We'll explore your goals, your home, and what's possible.
Schedule a Design Consultation →Typically a 45-minute conversation. No pressure, no obligation.