Free home addition estimator
What will your home addition cost?
Enter your addition's size, type, and finish level for an estimate built from current 2026 construction costs — per square foot and total.
What drives home addition cost
These factors move an addition budget the most.
Type of addition
Converting existing space is cheapest; a ground-level room addition is mid-range; second-story additions and ADUs cost the most per square foot.
Foundation & roof
New additions need their own foundation and a roof tie-in to the existing home, both major cost drivers.
Finishes
Whether the new space is a plain room or a full kitchen/bath dramatically changes the per-square-foot cost.
Permits & design
Structural work means permits, inspections, and often architectural or engineering plans.
Home addition cost by type (per square foot)
Typical 2026 installed cost ranges, materials and labor combined.
| Type | Per sq ft | 400 sq ft | Notes |
|---|
| Garage conversion | $50–$120 | $20,000–$48,000 | Uses existing structure |
| Bump-out | $150–$350 | smaller sizes | Small extension of a room |
| Sunroom | $100–$250 | $40,000–$100,000 | Often unconditioned |
| Room addition | $100–$220 | $40,000–$88,000 | Ground-level, new foundation |
| Second story | $150–$300 | $60,000–$120,000 | Structural reinforcement |
| ADU / in-law | $150–$350 | $60,000–$140,000 | Full independent living space |
Planning a DIY job?
Common materials and tools for this project. (Affiliate links — we may earn a commission at no cost to you.)
Home addition questions, answered
How much does a home addition cost in 2026?
Most home additions run $100 to $300 per square foot, so a 400 sq ft room addition typically lands around $40,000 to $90,000. Second-story additions and ADUs sit at the higher end.
What's the cheapest way to add square footage?
Converting existing space, like a garage or basement, is far cheaper than building new because the structure and roof already exist. Bump-outs are cheaper than full additions.
Do home additions add value?
Additions can add value, especially when they bring the home in line with neighborhood norms (like a needed bedroom or bathroom), but they rarely recoup 100% of cost at resale.
Do I need a permit for a home addition?
Almost always. Additions involve structural, electrical, and often plumbing work that require permits and inspections. Budget for permit fees and possible architectural or engineering plans.