What's the Difference Between a Garage Conversion and a New Construction ADU?
A garage conversion transforms an existing garage into a livable unit. New construction builds a separate dwelling from the ground up. Both result in a permitted ADU — they just start from different places and carry different cost, timeline, and flexibility tradeoffs.
The core distinction is whether there's an existing structure you can work with. In a garage conversion, the foundation, framing, and roof are already there. The project is about making the interior livable — insulation, electrical, plumbing, HVAC, windows, drywall, and finishes. In a new construction ADU, you're starting from scratch: site prep, foundation, framing, roofing, exterior, and everything inside.
Both paths go through the same permitting process in Vermont — zoning approval and a building permit from your local municipality. The end result is a legal, permitted accessory dwelling unit that can house family, generate rental income, or serve whatever purpose you have in mind.
Which One Costs Less?
Garage conversions typically cost $90,000–$160,000. New detached construction typically runs $180,000–$275,000. The savings in a conversion come from reusing the structure — you're not paying for foundation, framing, roofing, or exterior work.
Garage Conversion $90K–$160K
- Reuses existing foundation, framing, roof
- Lower labor and material costs
- May need floor raising if slab is at or below grade
- Cost rises if ceiling height is insufficient
- Utility connections often easier if near home
New Construction $180K–$275K
- Full site prep, foundation, framing, roofing
- Higher base cost but full design flexibility
- Place it anywhere on the lot that meets setbacks
- Better for larger units (800–1,200+ sq ft)
- Separate utility run may be required
One thing to watch: garage conversions can creep toward new construction cost if the existing structure needs significant work. A garage with a slab too low to the ground, a roof in poor condition, or inadequate ceiling height may require more structural intervention than expected. A good contractor will evaluate this in a site visit before pricing.
Which One Takes Less Time to Build?
Garage conversions typically take 6 to 10 months from consultation to move-in. New construction usually runs 10 to 16 months. Permitting timelines are similar for both — construction itself is where the time savings show up in a conversion.
Permitting is roughly the same for both project types. Vermont towns process ADU applications on their own schedules regardless of whether it's a conversion or new build — expect 4 to 12 weeks depending on the municipality and whether your project requires a hearing or variance.
Where conversions save time is in construction. When the shell is already standing, there's no excavation, no foundation pour, no framing phase, no roofing. You go straight to interior work. That can shave 2 to 4 months off the construction timeline, which matters a lot if you have a family member waiting to move in or are counting on rental income.
Does Your Garage Actually Qualify for Conversion?
A good garage conversion candidate has at least 8-foot ceiling height, a floor level near grade, adequate square footage for a livable unit, and accessible utility connections. Garages that fall short on these can still convert, but at higher cost.
Not every garage is a good ADU candidate, and the ones that look straightforward on paper sometimes aren't. Here's what matters most:
- Ceiling height: Vermont building code requires a minimum ceiling height for habitable space. Many older garages — particularly attached garages built alongside ranch-style homes — fall below 8 feet, which requires either a floor drop (expensive) or structural modifications.
- Floor level: A slab that sits significantly below grade creates drainage and moisture issues. Addressing this adds cost and complexity.
- Square footage: A one-car garage is typically 200–300 square feet — tight for a full ADU. A two-car garage gives you 400–600 square feet, which is workable. More is better.
- Utility access: How far is the garage from the main home's electrical panel, water supply, and sewer line? Short runs are easy. Long runs add cost.
- Structural condition: An older garage with a deteriorating foundation, rotted sill plates, or a roof that needs replacement changes the math significantly.
The only way to know for sure is a site visit. We evaluate garage conversion potential as part of our free consultation — we'll tell you honestly whether your garage is a good candidate and what the realistic scope of work looks like.
Which Type Is Right for Your Property?
If your garage is structurally sound and large enough, conversion is almost always the better starting point — lower cost, faster timeline. If your garage doesn't qualify or you want a larger, more independent unit, new construction gives you full design control and placement flexibility.
The decision usually comes down to what your property actually offers. If you have a solid two-car garage close to the main home's utilities, conversion is a clear winner on cost and speed. You sacrifice some design flexibility — you're working within an existing footprint — but for most ADU purposes, that tradeoff is worth it.
New construction makes more sense when: your garage isn't viable; you want a larger unit than your garage allows; you want to place the ADU at a specific spot on the lot for privacy or yard access reasons; or you want the ADU to be fully architecturally distinct from the existing home.
It's also worth noting that these aren't the only two options. Above-garage additions, basement conversions, and attached additions are all paths worth considering depending on your lot and your goals. We talk through all of them at the consultation stage so you can make the decision with full information.