Garage Conversion Cost Estimator
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How it works
A garage conversion is the cheapest square footage you will ever add — the foundation, walls and roof already exist. Typical conversions run $50–95 per sq ft versus $150–300+ for a ground-up addition.
The budget drivers are plumbing (a full bathroom adds $12,000+ — the slab must be cut for drains) and HVAC (a mini-split at ~$4,500 is the standard answer; extending ductwork is cheaper only if the system has spare capacity).
The unsexy part matters most: permits and zoning. Unpermitted conversions can block a future sale and void insurance. Some cities require you to replace the lost parking space, and HOAs often ban conversions outright — verify before spending a dollar.
Frequently asked questions
How much does it cost to convert a garage?
A basic 400 sq ft bedroom conversion runs $20,000–30,000; a full ADU with kitchen and bath runs $40,000–70,000+. Plumbing and finish level drive the range.
Do I need a permit?
Yes — virtually everywhere. Electrical, plumbing, structural and egress changes all need permits and inspections. Unpermitted work can kill a future sale and void your homeowner's insurance.
Can I convert a garage into a legal ADU?
In many cities, yes — garage ADUs are explicitly encouraged. You will need a separate entrance, kitchen, bathroom, egress windows and dedicated HVAC. Check local ADU ordinances for size caps and parking rules.
What about the garage door?
It gets removed and framed in with a proper insulated wall and windows. Budget $1,500–3,000 for the infill, flashing and exterior siding match.
Will the floor be level with the house?
Garage slabs usually sit 4–8 inches lower and slope toward the door. Options: a raised subfloor ($2,000–4,000) or self-leveling compound. Do not skip this — tripping thresholds and moisture issues follow.
How do I heat and cool it?
A ductless mini-split ($3,500–5,500 installed) is the standard answer — no ductwork, zoned control, efficient. Extending existing HVAC only works if the system was sized with spare capacity.
Does a conversion add home value?
Permitted living-space conversions generally add value at $100–200/sq ft of appraised space — often more than they cost. Unpermitted ones can subtract value by complicating the sale.
What is the biggest hidden cost?
Plumbing in the slab. Cutting concrete for bathroom drains runs $3,000–6,000 before a single fixture is set. If you can keep the bathroom on an exterior wall near existing lines, costs drop.
Will my HOA allow it?
Many do not — check CC&Rs before planning. Even without an HOA, some cities require replacing the lost covered parking with a carport or driveway pad.
How long does it take?
6–12 weeks for a bedroom/office; 3–5 months for an ADU with kitchen and bath. Permit approval is usually the longest phase — apply early.