Guide · Garage conversions

Converting a Denver garage into an ADU (2026)

LAST VERIFIED: SEPTEMBER 2026 · SOURCES: DENVER BUILDING CODE, DENVER CPD, PUBLISHED DENVER BUILDER PRICING

Direct answer: Converting a detached garage into an ADU in Denver typically costs $120K-$200K all-in and takes 5-9 months including permits, cheaper and faster than a new detached unit because the shell exists, but rarely as cheap as owners expect: the slab, the roof, and the utility connections usually all need work. The garage must sit on a lot that allows an ADU, meet the same setbacks as a new build if it's altered, and get a full building permit; you cannot legally "just add a kitchen."

§1, WHAT THE CONVERSION ACTUALLY INVOLVES

Why a garage conversion isn't a renovation

Legally it's a change of use, from accessory storage to a dwelling, and the code treats it as one. That means: a foundation that meets residential standards (many older Denver garage slabs are thin, uninsulated, and need to be cut or replaced); insulated walls and roof to current energy code; egress windows; a dedicated electrical service or a substantial sub-panel; plumbing runs for kitchen and bath, usually trenched back to the main house or the alley main; and fire separation if the garage is close to the property line. Owners who budget for "finishing the garage" and get quoted $150K are seeing this list for the first time.

GARAGE CONVERSION, WHERE THE MONEY GOES (TYPICAL DENVER RANGES, 2026)
Item	Range	Notes
Design + structural engineering	$8K-$20K	Engineer must assess the existing slab and framing
Foundation / slab work	$10K-$40K	The biggest variable; some slabs are unsalvageable
Plumbing + sewer connection	$15K-$35K	Distance to the main line drives cost
Electrical service	$8K-$18K	New meter or sub-panel; Xcel coordination
Envelope, windows, roof	$25K-$50K	Insulation, egress windows, often a new roof
Interior finish, kitchen, bath	$40K-$70K	Same as any small dwelling
Permits + Denver Water SDC	$7K-$13K	See costs for the fee breakdown

§2, CONVERT OR REPLACE?

When knocking it down is cheaper

If the slab needs replacing and the roof structure can't carry insulation and drywall, a conversion can cost within 10-15% of a new detached ADU on the same footprint, with less design freedom and the old garage's height limits. The honest test: ask the builder for a conversion quote and a demolish-and-rebuild quote side by side. Experienced Denver ADU builders will give both; a contractor who only offers one has usually decided based on what they prefer to build.

Height matters too. Denver's 24-foot / 1.5-story limit for detached ADUs means a rebuild can add a second level where the original garage couldn't, often the difference between a studio and a real one-bedroom.

§3, WHO DOES THIS WORK

Finding a garage-conversion builder

Conversions reward builders who've done them repeatedly, because the surprises live inside the existing structure. In the directory, design-build firms and ADU specialists list conversion work most often; ask specifically how many garage conversions they've completed in Denver, and whether any hit a slab or foundation problem, the answer to the second question tells you whether they've done enough to have met one. Run the same vetting checks as for any ADU.

Independent guide. Directory listings are free; no company pays to appear or be removed. One disclosed sponsored placement may appear, labeled "Featured builder, paid sponsorship"; it never changes what we publish. Verify rules and fees with Denver CPD before relying on them.