Cost guide
Addition Cost
How much does an addition to a house cost? The short answer is that it depends on type, size, finish, foundation, features, and state — which is why this guide prices each of those separately instead of offering a single average.
Start with the calculator for your own project, then use the table below to sense-check the result. A bid that is far below the range for the same scope should be questioned, and so should one far above it.
Cost per square foot by addition type and finish
| Addition type | Economy | Standard | Premium |
|---|---|---|---|
| Room / Bedroom | $80–$130 | $130–$200 | $200–$350 |
| Kitchen Extension | $150–$220 | $220–$350 | $350–$500 |
| Bathroom | $200–$250 | $250–$350 | $350–$500 |
| Sunroom | $100–$150 | $150–$225 | $225–$350 |
| Second Story | $200–$300 | $300–$450 | $450–$600 |
| Attached Garage | $50–$80 | $80–$120 | $120–$175 |
| ADU / In-Law Suite | $150–$200 | $200–$300 | $300–$450 |
Ranges are planning figures per square foot before foundation and optional features. The calculator below applies the same midpoints: for example, a Standard room addition uses $165 per square foot at the national average.
Example totals at the national average
A 400 sq ft Standard room addition on a slab centres on $66,000. The same area as a kitchen extension centres on $114,000, as a bathroom on $120,000, as a sunroom on $74,800, as a second story on $150,000, as a garage on $40,000, and as an ADU on $100,000 — all before foundation upgrades, features, and the state index. Those differences are the reason the addition type must be chosen first.
What the estimate includes — and what it does not
The estimate includes the structure, the foundation you select, and the features you select. It does not itemise design and permit fees, rock or poor soil, outdated wiring or plumbing in the existing house, landscaping, or furniture. Keep a 10–20% contingency for those items, and get itemised local bids before committing.
Calculators
Room Cost Calculator
Room, office, and living-space additions by size and finish.
Second Story Calculator
Building up: second-storey prices with roof, HVAC, and plumbing allowances.
Cost by state
- California home addition cost
- Texas home addition cost
- Florida home addition cost
- New York home addition cost
- North Carolina home addition cost
- New Jersey home addition cost
- Arizona home addition cost
- Minnesota home addition cost
- Colorado home addition cost
- Georgia home addition cost
- Ohio home addition cost
- Massachusetts home addition cost
- Pennsylvania home addition cost
- South Carolina home addition cost
Frequently asked questions
How much is an addition?
A typical single-room addition centres on tens of thousands of dollars, depending on size and finish. Use the calculator with your size, type, and finish for a figure for your project.
What is the cost to expand a house?
Expanding a house usually means a room, kitchen, or second-story addition. The table above gives per-square-foot ranges for each type; the calculator combines them with foundation, features, and state.
What is the price of an addition to a house?
There is no single price. The price is size times rate, plus foundation and features, adjusted for state. The worked examples above show how the same size gives very different totals for different types.
Planning estimate only, based on 2026 cost data. It is not a quote. Get itemised bids from licensed local contractors before building, and set aside a 10–20% contingency for permits, design fees, and site surprises.