Garage Conversion Contractor
Turn the garage into a bedroom, a studio, an office or a full ADU — permitted and built properly.
A garage is usually the cheapest square footage on a property to make liveable. The foundation, the walls and the roof already exist — you are paying to finish a space rather than build one. In the South Bay, where land is the expensive part, that makes a garage conversion one of the best returns available on a house you already own.
D One Builders is a licensed general contractor (CSLB #1028049) in Gilroy. We convert attached and detached garages across San Jose, Gilroy, Morgan Hill, Santa Clara, Cupertino, Los Gatos and Hollister.
What a Garage Conversion Costs
Most garage conversions run $60,000 to $150,000. Converting to a bedroom, office or studio sits at the lower end. Converting to a full ADU — kitchen, bathroom, separate entrance — lands at the upper end, because you are adding plumbing, a second electrical load and often a sewer connection.
For comparison, a new detached ADU typically runs $180,000 to $350,000. The conversion is cheaper because you are not buying a foundation, framing or a roof. What you give up is the garage and the freedom to choose your own footprint.
What You Can Turn It Into
A full ADU. Kitchen, bathroom, separate entrance — a legal second dwelling that can be rented. ADUs in this market commonly rent for $2,500 to $4,000 per month, which is what makes the payback maths work.
A bedroom or guest suite. The simplest and cheapest version. No kitchen, so no second utility connection, and often no bathroom either if one is close by.
An office or studio. A conditioned, insulated, properly wired room that is separate from the noise of the house — without the cost of a full dwelling.
A gym or workshop. Less regulated, since it is not habitable space, but still worth insulating and wiring properly.
What the Work Actually Involves
A garage is an unconditioned shell. Making it habitable means insulation, drywall, egress windows that meet code, adequate ceiling height, a level floor, HVAC, electrical, and fire separation between the space and the house. The garage door opening is normally framed in and replaced with a wall and windows — which, done well, is what stops the finished room reading as a converted garage.
If it is becoming an ADU, add plumbing, a kitchen and a bathroom. That is the single biggest cost step, and it is the difference between the two ends of the price range.
Permits, and the Parking Question
You need a permit. Always. Unpermitted conversions cause real trouble at resale and with insurance, and cities do find them.
Two pieces of California law make this easier than it used to be. Cities must review compliant ADU applications ministerially — an over-the-counter approval rather than a hearing where neighbours object. And the replacement-parking requirement, historically the biggest obstacle to garage conversions, has been removed in many situations. Both still depend on your lot and your city, so we confirm them before anyone pays for drawings. See our South Bay permits guide for how the local departments differ.
Attached or Detached
Detached garages often make the better ADU — genuine privacy, a separate entrance, and no reconfiguring of the main house. The main cost variable is running utilities out to it.
Attached garages are cheaper to service because the utilities are right there, but they need careful fire separation and sound isolation from the house, and the entrance takes more thought.
Where We Work
San Jose, Gilroy, Morgan Hill, Los Gatos, San Martin, Hollister and San Benito County. Also see ADU construction and home additions if you are weighing the options.
Garage conversion questions
How much does a garage conversion cost?
Most garage conversions run $60,000 to $150,000 in the South Bay. A conversion to a bedroom or office sits at the lower end. Converting to a full ADU with a kitchen, bathroom and separate entrance lands at the upper end, because you are adding plumbing, a second electrical load and often a new sewer connection. The shell already existing is what makes this cheaper than building new — you are not paying for a foundation, walls or a roof.
Is a garage conversion cheaper than building an ADU from scratch?
Usually yes, and often by a wide margin. A detached ADU typically runs $180,000 to $350,000 because it needs its own foundation, framing, roof and utility runs. A garage conversion reuses all of that. The trade-off is that you give up the garage and you are constrained by its existing footprint and ceiling height.
What is involved in converting a garage?
The work is mostly bringing an unconditioned space up to habitable standard: insulation, drywall, proper egress windows, ceiling height, floor levelling, HVAC, electrical, and fire separation from the house. If it is becoming an ADU, add plumbing, a kitchen and a bathroom. The garage door opening is usually framed in and replaced with a wall and windows.
Do I need a permit to convert my garage?
Yes, always. An unpermitted conversion causes real problems at resale and with insurance, and cities do find them. The good news is that California requires cities to review compliant ADU applications ministerially rather than through a discretionary hearing, which makes a garage-to-ADU conversion far more predictable to permit than most people expect.
Will I have to replace the parking?
In most cases no. California law has removed the replacement-parking requirement for ADU conversions in many situations, which was historically the single biggest obstacle. It still depends on your specific lot and city, so we confirm it before you spend money on drawings.
How long does a garage conversion take?
Typically four to eight months from first drawing to final inspection — roughly two to four months for design and permitting, and two to four for construction. It is faster than a new detached build because the structure is already standing.
Can I convert a detached garage?
Yes, and a detached garage often makes the better ADU because it gives the unit genuine privacy and its own entrance without reconfiguring the main house. Detached conversions sometimes need utility runs from the house, which is the main cost variable.
Talk to a Licensed Builder
No pressure and no sales pitch — just a straight answer on what your project takes and what it costs. D One Builders, CSLB #1028049.
Request a Free EstimateOr call 831-318-5896