Cost guide
Home Addition Cost in 2026
Adding square footage is one of the biggest investments you can make in a home. Type, foundation and finish level decide the price.
Step 1 of 4
Your addition
Size and type.
Labor costs differ a lot by state. This adjusts every line.
New finished floor area, not counting the existing house.
Type of addition
Foundation
Estimated addition cost
$113,900
$73,000 – $154,800
Want the line-by-line breakdown, with labor and materials split out for your state? Open the Home Addition Cost Calculator.
Home addition cost by type
| Scenario | Estimated range | Per sq ft |
|---|---|---|
| Bump-out (150 sq ft)A small extension, typically without a full foundation | $39,100 – $84,600 | $261–$564 |
| Ground-floor room (300 sq ft)Slab foundation, standard finishes | $73,000 – $154,800 | $243–$516 |
| Second-story addition (500 sq ft) with bathroom | $147,400 – $303,000 | $295–$606 |
| Sunroom (200 sq ft) | $37,000 – $88,200 | $185–$441 |
Estimates at national-average pricing, calculated with our own pricing engine and reviewed September 2026. Change the inputs in the calculator to price your exact project.
Home addition cost per square foot
All-in, a home addition costs about $235–$485 per square foot for a standard ground-floor room, $270–$550 for a second story, $215–$405 for a bump-out and $165–$375 for a sunroom. "All-in" means the structure, foundation, roof tie-in, heating and cooling, architect fees, permits and a contingency, not just the framing price a contractor may quote first.
Cost per square foot by type (400 sq ft each, no bathroom)
| Scenario | Estimated range | Per sq ft |
|---|---|---|
| Bump-outSmall extension, usually no full foundation | $85,800 – $162,600 | $215–$407 |
| Ground-floor roomBuilt on its own slab foundation | $93,700 – $193,800 | $234–$485 |
| Second-story additionBuilt over the existing house, no new foundation | $108,900 – $219,000 | $272–$548 |
| SunroomGlass-heavy, slab foundation | $66,200 – $149,400 | $166–$374 |
National average, slab foundation where one is needed, standard finishes. Set your state in the calculator above for a local number.
Home addition cost by size
Cost per square foot falls as an addition gets bigger, because design fees, permits and utility tie-ins are spread over more floor area. These rows price a ground-floor room on a slab with standard finishes.
| Scenario | Estimated range | Per sq ft |
|---|---|---|
| 200 sq ft additionAbout 14 × 14 ft | $52,400 – $115,800 | $262–$579 |
| 300 sq ft additionAbout 12 × 25 ft | $73,000 – $154,800 | $243–$516 |
| 400 sq ft additionAbout 20 × 20 ft | $93,700 – $193,800 | $234–$485 |
| 600 sq ft additionA large family room or primary suite | $135,100 – $271,800 | $225–$453 |
| 800 sq ft addition | $176,400 – $349,800 | $221–$437 |
| 1,000 sq ft addition | $217,800 – $427,800 | $218–$428 |
Estimates at national-average pricing, calculated with our own pricing engine and reviewed September 2026. Change the inputs in the calculator to price your exact project.
What moves the cost per square foot
- Finish level. Basic finishes bring a 400 sq ft room to about $205–$430 per square foot; high-end custom finishes push it to $295–$595.
- Foundation. A full basement raises the same room to about $255–$520 per square foot. A slab is the cheapest, a crawlspace sits in between.
- Bathroom or kitchen. A bathroom adds about $12,000–$30,000 and a kitchen $15,000–$40,000 before contingency, which lifts the per-square-foot price of a small addition sharply.
- Location. Labor and material costs vary a lot by state. The calculator adjusts every line for yours.
What drives the cost
- Type matters most: a second story costs more per sq ft than a ground-floor room, but needs no new foundation.
- Bathrooms and kitchens are plumbing-heavy and can add $30k–$70k.
- Architect fees, permits and utility tie-ins are often missing from rough quotes.
- Additions carry more unknowns, so this estimate includes a larger contingency.
Ways to keep an addition affordable
- Build up or out with the simplest roof line. Complex rooflines add cost fast.
- A slab or crawlspace costs far less than a full basement.
- Keep plumbing near existing lines; a bathroom or kitchen can add $30k or more.
- Budget for architect fees, permits and a real contingency before you commit.
Frequently asked questions
How much does a home addition cost per square foot?
Roughly $235–$485 per square foot for a standard ground-floor room, all-in. A second story runs about $270–$550, a bump-out $215–$405 and a sunroom $165–$375. These are national averages for a 400 sq ft addition. Smaller additions cost more per square foot, and prices vary by state, so set yours in the calculator.
How much does a 400 sq ft addition cost?
About $94,000–$194,000 for a ground-floor room (roughly 20 × 20 ft) on a slab with standard finishes. A 300 sq ft room costs about $73,000–$155,000, an 800 sq ft addition about $176,000–$350,000 and a 1,000 sq ft addition about $218,000–$428,000. A bathroom, kitchen, full basement or high-end finishes raise these numbers.
Why does a small addition cost more per square foot?
Design fees, permits, utility tie-ins and the roof connection cost about the same whether the room is 150 or 400 square feet. On a small room those fixed costs are spread over fewer square feet, so each one costs more.
Is it cheaper to build up or build out?
A ground-floor room is usually cheaper per square foot (about $235–$485 against $270–$550 for a second story). Building up avoids a new foundation and keeps your yard, but it needs structural reinforcement and a rebuilt roof.
Related guides
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- Basement Finishing Cost in 2026Finishing a basement adds living space without changing your home’s footprint.
- 10 Hidden Costs of Home Renovation (2026)These surprise costs have blown up thousands of renovation budgets.