Cost Guides
Home Addition Cost in the USA 2026: Room-by-Room Breakdown
What a bump-out, a full room addition, a second story and a sunroom cost in 2026 — with the foundation, framing, MEP and finish line items behind the number.
Additions are new construction attached to an old house
An addition is the most expensive per-square-foot work most homeowners ever commission because it involves every trade: excavation, foundation, framing, roofing, siding, windows, electrical, plumbing, HVAC, insulation, drywall and finishes. Nothing is reused.
It also carries a cost no other project has — tying new construction into an existing structure whose framing, roofline and utility capacity were never designed to accept it.
2026 addition costs by type
National average installed ranges, excluding land, landscaping restoration and furnishings.
| Addition type | Typical size | $/sq ft | Total range |
|---|---|---|---|
| Bump-out (cantilever, no foundation) | 20–60 sq ft | $150–$300 | $4,000–$18,000 |
| Single-room addition (bedroom) | 200–300 sq ft | $130–$250 | $26,000–$75,000 |
| Primary suite with bath | 300–450 sq ft | $180–$350 | $54,000–$158,000 |
| Kitchen expansion | 150–300 sq ft | $200–$400 | $30,000–$120,000 |
| Family room addition | 300–500 sq ft | $120–$240 | $36,000–$120,000 |
| Second-story addition | 600–1,200 sq ft | $180–$350 | $108,000–$420,000 |
| Four-season sunroom | 150–250 sq ft | $150–$300 | $22,500–$75,000 |
| Three-season sunroom | 150–250 sq ft | $90–$180 | $13,500–$45,000 |
| Garage (detached, 2-car) | 440–600 sq ft | $60–$130 | $26,000–$78,000 |
| ADU / in-law suite | 400–800 sq ft | $200–$400 | $80,000–$320,000 |
Where the budget goes on a 300 sq ft room addition
This is a representative line-item split for a $60,000, 300 sq ft addition at mid-range finish. Use it to sanity-check a contractor's breakdown.
| Line item | Share | Approx. cost |
|---|---|---|
| Design, engineering, permits | 6–10% | $3,600–$6,000 |
| Excavation and foundation | 12–18% | $7,200–$10,800 |
| Framing and sheathing | 15–20% | $9,000–$12,000 |
| Roofing and siding | 10–14% | $6,000–$8,400 |
| Windows and exterior doors | 6–10% | $3,600–$6,000 |
| Electrical, plumbing, HVAC | 14–20% | $8,400–$12,000 |
| Insulation and drywall | 8–10% | $4,800–$6,000 |
| Flooring, trim, paint | 10–14% | $6,000–$8,400 |
| Contingency | 10% | $6,000 |
The costs people forget
Additions routinely blow budgets on items outside the addition itself. Your existing electrical panel may need an upgrade to carry new circuits ($1,800–$4,500). Your furnace or heat pump may be undersized for the added conditioned volume ($4,000–$12,000 for a replacement, or $2,500–$6,000 for a ductless zone). An older roof will now be half new and half aged, and matching shingles across a 12-year age gap never quite works.
Add site restoration too: excavation equipment destroys lawns, driveways and irrigation. Budget $2,000–$8,000 to put the yard back.
- Electrical panel upgrade: $1,800–$4,500
- HVAC capacity or new zone: $2,500–$12,000
- Roof tie-in and shingle matching: $1,500–$6,000
- Site and landscape restoration: $2,000–$8,000
- Temporary housing if the kitchen or only bath is affected
Second story vs building out
Going up avoids losing yard and avoids new foundation work — but it requires verifying that the existing foundation and first-floor walls can carry the load, temporary weather protection for an open house, and usually full relocation of the family for 3–6 months. Going out costs less per square foot but consumes lot area and may hit setback limits.
In most markets, building out is 15–30% cheaper per square foot than building up. Building up wins when the lot is small, setbacks are tight, or the yard is the property's main asset.
Permits and timeline
Expect 4–12 weeks for design and permitting before ground breaks, then 3–6 months of construction for a single-room addition and 4–8 months for a second story. Any addition changes the building footprint, so it requires a permit and inspections everywhere in the US — there is no version of this that is legally skippable.
Tools & guides for this project
Material Cost Calculator
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Waste Factor Calculator
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Project Budget Calculator
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Labor Cost Calculator
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