Why garage conversions are popular
A garage conversion reuses the existing foundation, framing, and roof, which typically lowers cost and shortens timeline compared to building a new detached ADU from scratch. For homeowners with an underused or rarely-used garage, converting it can be the fastest path to a legal second unit.
What you give up
Once your garage becomes an ADU, you lose that covered parking and storage space, which some homeowners underestimate until the project is underway. Garages also were not originally built as living space, so insulation, flooring height, ceiling height, and window placement often need real work to meet livability and building code standards — a conversion is rarely as simple as "finishing" the space.
Structural considerations
Garage conversions still require full permit review, and in many cases still need foundation, electrical, and structural upgrades to meet current residential code, since garages were built to a different structural standard than living space. An experienced contractor will evaluate this on-site before quoting a project as a simple conversion.
When new-construction detached ADU makes more sense
If you use your garage regularly for parking or storage, or your garage's structure and layout would require extensive rework to meet code, a new detached ADU may end up being a more efficient use of budget than trying to save cost on an conversion that needs significant structural work anyway. See our detached vs. attached ADU guide for that comparison.
Getting an honest evaluation
Whether a garage conversion is truly the cheaper, faster option depends entirely on your specific garage's condition. A contractor visiting the site is the only reliable way to know — request a match for an on-site evaluation.
Timeline differences worth knowing about
Because a garage conversion reuses an existing structure, the construction phase can sometimes move faster than a full new build once permits are approved. Permit review itself, however, generally takes similar time either way, since both project types go through the same jurisdictional process described in our permit process guide. Do not assume a conversion automatically means a dramatically shorter overall project timeline — ask your contractor for a realistic estimate specific to your property.
Parking requirements can factor into the decision
If your household relies on garage parking, losing that space is a real lifestyle tradeoff worth weighing against the cost savings of a conversion, independent of any local parking-replacement rules that may or may not apply to your specific project under current state and local law.
Have a question about your specific project?
Call (877) 300-2747 or request a match, and mention you have questions related to “ADU vs. Garage Conversion” — we will route you to a licensed contractor who can speak to it directly.