Garage addition cost = floor area × about $75 per sq ft for a finished, insulated garage; a 24 x 24 ft attached garage on a slab foundation costs about $43,000 at US-average prices ($23,000 to $62,000), and the garage foundation alone is about $4,600. Fixr's national average for an attached garage is $37,000.
How the garage addition cost is calculated
Fixr's attached garage guide (August 2025) lists what each part of a garage costs, and its size table puts a conventional 24 x 24 ft garage at $34,560 to $46,080 ($60 to $80 per sq ft). The calculator treats the component ranges as those of the 24 x 24 ft garage (576 sq ft) and scales them to your size; that reading is ours, not a statement on Fixr's page.
| Part | Range for a 24 x 24 ft garage | Source |
|---|---|---|
| Excavation and site prep | $3,500 to $5,700 | Fixr |
| Framing and drywall | $4,500 to $10,500 | Fixr |
| Roof | $3,000 to $5,000 | Fixr |
| Siding, vinyl | $3,000 to $9,000 | Fixr |
| Insulation | $600 to $8,000 | Fixr, HomeAdvisor ($1,900 to $7,700) |
| Floor finish | $1,400 to $3,000 | Fixr |
| Electrical and lighting | $720 to $3,000 | Fixr |
| Garage door: single / double | $600 to $1,500 / $800 to $3,500 | HomeAdvisor |
| Door opener | $220 to $520 | HomeAdvisor |
| Permits | $1,200 to $1,500 | HomeAdvisor |
| Driveway to the doors | $3,000 to $10,000 | Fixr |
Cost = area × (foundation + framing + roof + siding [+ insulation + floor]) + site prep + doors + electrical + permits + 10% contingency
Garage foundation cost
The foundation is priced per square foot by type from Fixr's concrete foundation guide (February 2026), where labor is 40% to 60% of the cost:
| Foundation | Per sq ft | 24 x 24 ft (typical) |
|---|---|---|
| Slab on grade | $4 to $12 | $4,600 |
| Monolithic slab | $4 to $16 | $5,800 |
| Stem wall slab | $6 to $18 | $6,900 |
A plain slab on grade suits mild climates on level ground. A monolithic slab is poured with a thickened edge in one go. A stem wall slab carries footings below the frost line and is the usual choice where the ground freezes. Fixr's attached garage guide puts foundation and slab at $2,500 to $3,400 and HomeAdvisor's garage guide at $2,000 to $7,000. Size the concrete with the concrete slab calculator or, for footings, the concrete footing calculator.
Worked example: 24 x 24 ft, slab, insulated, one double door
| Line | Typical |
|---|---|
| Excavation and site prep | $4,600 |
| Foundation, slab on grade, 576 sq ft × $8 | $4,600 |
| Framing and drywall | $7,500 |
| Roof | $4,000 |
| Siding | $6,000 |
| One double garage door | $2,150 |
| Opener | $370 |
| Electrical and lighting | $1,850 |
| Insulation | $4,550 |
| Floor finish | $2,200 |
| Permits | $1,350 |
| Contingency, 10% | $3,800 |
| Total | $43,000 (range $23,000 to $62,000) |
Without the contingency it is $39,000, inside Fixr's $34,560 to $46,080. The $23,000 low end matches the low of Fixr's typical range for an attached garage. A stem wall foundation raises the total to $45,500.
Cost by size
| Size | Area | Typical |
|---|---|---|
| 12 x 20 ft, single door | 240 sq ft | $23,000 |
| 20 x 20 ft, one double door | 400 sq ft | $33,500 |
| 24 x 24 ft, one double door | 576 sq ft | $43,000 |
Fixr's conventional prices for 12 x 20 ft ($14,400 to $19,200) and 30 x 20 ft ($36,000 to $48,000) show the same shape: small garages cost more per square foot because the site prep, electrical, door and permit are close to fixed.
What raises the price
- Foundation and site. A sloped lot, poor soil or frost-depth footings.
- Tie-in to the house. Matching the roofline and siding, plus a fire-rated wall and door between the garage and the house.
- Doors. A double door is $800 to $3,500, an insulated carriage-style door more.
- Living space above. HomeAdvisor adds $125 to $250 per sq ft for finished living space above a garage; the calculator prices the garage only.
Permits
An attached garage needs a building permit almost everywhere, plus a fire separation between garage and house. Setbacks and lot coverage decide how big it can be.
What to work out next
Order the roofing and the drywall, and to turn an existing garage into a room see the garage conversion cost calculator. A bigger addition is priced in the home addition cost calculator. All estimates are in the project costs hub.
These are dated estimates from published national data adjusted for your state, not a quote.