A garage with an apartment above is two buildings stacked into one. The garage underneath is simple: a slab, walls, a door. The apartment on top is a small house, with a kitchen, a bathroom, heating and cooling, stairs and the fire separation the code requires between cars and people. That is why the second floor costs several times what the garage below it does.
HomeGuide puts a garage with an apartment at $200 to $350 per square foot, or $80,000 to $300,000 in total depending on size. A 24 by 24 foot garage with an apartment above costs $115,000 to $200,000.[1] HomeAdvisor gives $175,000 as the cost to build an apartment over a garage.[2] Here is what goes into that number.
Key takeaways
- HomeGuide: $200 to $350 per square foot; $115,000 to $200,000 for a 24×24 garage with an apartment.
- Living space above a garage costs $125 to $200 per square foot against $60 to $80 for the garage alone (Fixr).
- The IRC requires 5/8 inch Type X gypsum board between the garage and habitable rooms above.
- Check your town’s accessory dwelling rules before you design anything; they decide whether you can rent it.
Cost by size
| Garage size | Apartment area | Total cost |
|---|---|---|
| 20 × 20 ft | 400 sq ft | $80,000 to $140,000 |
| 20 × 24 ft | 480 sq ft | $96,000 to $168,000 |
| 24 × 24 ft | 576 sq ft | $115,000 to $200,000 |
| 36 × 24 ft | 864 sq ft | $173,000 to $300,000 |
Compare that with the garage alone. HomeGuide puts a detached garage without living space at $50 to $100 per square foot, or $20,000 to $57,600 for a two-car garage.[1] Fixr makes the same point another way: it says finishing living space above a garage, with plumbing, wiring and HVAC extended to it, moves the cost from $60 to $80 per square foot to $125 to $200, more than doubling it.[3]
Where the money goes
HomeGuide breaks a garage with an apartment into its parts. The per-square-foot lines show why the upper floor costs so much more than the garage: it needs everything a house needs.
| Item | Cost |
|---|---|
| Concrete foundation | $5 to $33 per sq ft |
| Framing | $11 to $30 per sq ft |
| Drywall | $1.50 to $3.50 per sq ft |
| Insulation | $0.50 to $3.00 per sq ft |
| Flooring | $4 to $15 per sq ft |
| Plumbing | $4 to $5 per sq ft |
| Electrical wiring | $4 to $9 per sq ft |
| HVAC | $3 to $6 per sq ft |
| Cabinets | $150 to $500 per linear ft |
| Countertops | $50 to $150 per sq ft |
| Kitchen appliances | $2,500 to $6,800 |
| Toilet | $350 to $800 each |
| Exterior door | $300 to $1,000 each |
| Window | $450 to $1,500 each |
Notice the foundation range: $5 to $33 per square foot, far wider than for a plain garage. A second story puts much more weight on the footings, so they are often deeper and wider. If there is any chance you will add a floor later, size the foundation for it from the start. Our guide to garage slab costs covers what changes.
The fire separation between cars and people
Cars, fuel and solvents sit directly under a bedroom, so the code treats the floor between them as a fire barrier. The 2021 International Residential Code requires at least 5/8 inch Type X gypsum board, or equivalent, between the garage and habitable rooms above it. The walls and beams that support that floor need at least 1/2 inch gypsum board too.[4] Any door from the garage into the living space has to be solid wood or steel at least 1-3/8 inches thick, or 20-minute fire-rated, and self-closing and self-latching. A garage door can't open directly into a bedroom.[4]
Ducts that pass through the separation, and any other penetrations, have their own rules as well. None of this is expensive if it is designed in, but it is a common reason for failed inspections when a storage loft is later turned into a room.
Check the zoning before the design
An apartment above a garage is usually an accessory dwelling unit in zoning terms, and towns regulate those separately from garages. The rules can cover the maximum size of the unit, the building's height and setbacks, whether the owner must live on the property, parking for the tenant, and whether you can rent it at all. Some towns encourage them; others ban them in certain zones.
Ask the planning department three questions before you pay for drawings: is an accessory dwelling allowed on your lot, how big can it be, and how tall can the building be? The height limit is the one that surprises people, because a two-story garage is often taller than the house next to it. HomeGuide also notes that additional structural, electrical and plumbing work may need multiple permits beyond the garage building permit.[1]
Storage loft or living space?
A storage loft under attic trusses is much cheaper than a room, because it needs no plumbing, heating or fire-rated floor beyond the basic separation. But it can't legally become a bedroom without meeting the code for habitable space. If you might want a room or apartment later, design and permit for it now, even if you leave it unfinished.
Prefab and conversion options
Prefab garages with an apartment space above cost less to buy, but most of the work is still ahead of you. HomeGuide puts them at $60 to $100 per square foot, or $35,000 to $100,000, usually delivered with doors, windows, a roof and siding but otherwise unfinished. You still add flooring, electrical, plumbing and HVAC.[1] HomeAdvisor puts a two-story prefab garage at $20,000 to $150,000 before delivery and installation, and says finishing the second story as an apartment costs another $30,000 to $150,000.[5]
If you already have a garage, HomeGuide puts adding a second story at $60,000 to $200,000 or more, and converting the garage itself into living space at $5,000 to $50,000 or more.[1] Adding a story depends entirely on whether the existing foundation and walls can carry it, which an engineer needs to check.
Estimating your own
In our garage cost calculator, choose Room or Apartment under living space above. A room is priced at Fixr's $125 to $200 per square foot of upper floor. An apartment adds a kitchenette (10 feet of cabinets, 25 square feet of countertop and a set of appliances) and bathroom plumbing at HomeGuide's rates. A 24 by 24 detached garage with a 576 square foot apartment and frost footings comes to about $157,000 in construction, or about $190,000 with a 10% builder fee and 10% contingency, within HomeGuide's $115,000 to $200,000 range. The research behind the calculator lists every line and source.
Building as part of a new house? The guide to garage cost when building a house covers how a garage fits the lot and the plan.
Add living space above in the garage calculator and see how it changes the whole budget.
Frequently asked questions
How much does it cost to build a garage with an apartment?
HomeGuide puts it at $200 to $350 per square foot, or $80,000 to $300,000 depending on size. A 24×24 garage with an apartment above costs $115,000 to $200,000.
Is a garage apartment cheaper than a separate ADU?
It can be, because the apartment shares a foundation and roof with the garage. But the fire separation, stairs and stronger footings add cost, so get quotes for both if your lot allows either.
What fire rating is needed between a garage and an apartment above?
The 2021 IRC requires at least 5/8 inch Type X gypsum board between the garage and habitable rooms above, with 1/2 inch gypsum board on the supporting structure.
How much does a prefab garage with an apartment cost?
HomeGuide puts prefab garages with an apartment at $60 to $100 per square foot, or $35,000 to $100,000, usually unfinished inside, so flooring, wiring, plumbing and HVAC are extra.
Can I rent out an apartment above my garage?
It depends on your town’s accessory dwelling rules, which can limit the unit size, height, parking and whether the owner must live on the property. Check before you design it.
Sources
- HomeGuide, "How Much Does It Cost to Build a Garage with an Apartment?", February 18, 2026 Verified
- HomeAdvisor, "Garage Cost Guides", updated June 17, 2026 Verified
- Fixr, "Cost to Build an Attached Garage", updated August 29, 2025 Verified
- International Code Council, 2021 International Residential Code, Sections R302.5 and R302.6 (dwelling-garage separation) Verified
- HomeAdvisor, "How Much Does a Prefab Garage Cost?", updated June 17, 2026 Verified
Figures last checked October 25, 2026. National averages are a planning guide, not a quote. See our editorial policy and data sources.
