A home addition costs $100 to $300 per square foot finished, or $30,000 to $100,000 for a typical project.3 Building out runs $80 to $250 per square foot; building up (a second story) runs $200 to $500+.12 Fixr’s national average is $65,000; Angi’s is $50,986.13 Prices below are national averages* for 2026.
*National averages, not local quotes. Your price depends on addition type, size, plumbing needs, structural work, and local labor rates.
$125 – $250
per sq. ft., HomeGuide
$65,000
average addition, Fixr
$80 – $200
per sq. ft. building out, Angi
40 – 60%
labor share, Angi
Quick math: the per-foot bands disagree — Angi says $80 to $200 building out, HomeGuide $125 to $250, Fixr $100 to $300. On a 400 sq. ft. addition that is $32,000 to $80,000 vs. $50,000 to $100,000 vs. $40,000 to $120,000, our arithmetic.123 The middle of the overlap, roughly $50,000 to $80,000, is the realistic planning range for a 20′×20′ room.
Cost by size
| Addition size | HomeGuide ($125–$250/sf) | Fixr ($100–$300/sf) |
|---|---|---|
| 10′×10′ (100 sq. ft.) | $12,500 – $25,000 | — |
| 10′×20′ (200 sq. ft.) | $25,000 – $50,000 | $20,000 – $60,000 |
| 20′×20′ (400 sq. ft.) | $50,000 – $100,000 | $40,000 – $120,000 |
| 20′×30′ (600 sq. ft.) | $75,000 – $150,000 | $60,000 – $180,000 |
| 25′×40′ (1,000 sq. ft.) | $125,000 – $250,000 | $100,000 – $300,000 |
Each grid matches its per-foot band exactly — 400 sq. ft. × $125 to $250 = $50,000 to $100,000 (HomeGuide), our arithmetic.2 Fixr’s $65,000 national average is a 300 sq. ft. family room, about $217 per foot, our arithmetic — mid-band.3
Cost by type
| Addition type | Per sq. ft. | Typical total | Source |
|---|---|---|---|
| Bump-out (extend a room) | $85 – $200 | from $4,000 (laundry) | HomeGuide, Fixr |
| Room addition (build out) | $80 – $250 | $12,500 – $25,000 (10′×10′) | Angi, HomeGuide |
| Sunroom | $100 – $350 | $35,000 – $70,000 | HomeGuide, Fixr |
| ADU / in-law suite | $100 – $300 | $82,750 average | HomeGuide, Angi |
| Bathroom addition | — | $18,000 – $70,000 | Fixr |
| Kitchen addition | — | $30,000 – $100,000 | Fixr |
| Primary suite | — | $45,000 – $135,000 | HomeGuide |
| Second story (build up) | $200 – $500+ | $175,000 average | HomeGuide, Angi |
Rooms with plumbing cost the most per foot: bathrooms and kitchens outprice bedrooms because fixtures, rough-in, and waterproofing stack up.23 Building up costs 2 to 3 times building out — Angi’s 10′×10′ is $12,500 out versus $40,000 up, our ratio1 — because the foundation, walls, and roof all need structural changes (HomeGuide).2
Labor, plans, and permits
Labor is 40 to 60% of the total (Angi) — on Fixr’s $65,000 average that is $26,000 to $39,000, our arithmetic.13 Architect or engineer plans run $1,200 to $5,000 (HomeGuide) or $2,400 to $14,000 (Angi); structural drawings alone are $500 to $2,000.12 Building permits span $150 to $7,500, and site prep adds $1,500 to $5,000 (Angi).1 Sub-line-items: foundation $5 to $37 per sq. ft., framing $4 to $16, roofing $4 to $11 (Angi).1
Worked examples
Example 1 — 20′×20′ family room, build out. HomeGuide: 400 sq. ft. × $125 to $250 = $50,000 to $100,000, our arithmetic.2 Fixr: $40,000 to $120,000 for the same 400 sq. ft.3 The $50,000 to $100,000 overlap is the planning number.
Example 2 — small bump-out, laundry room. Fixr’s low-end project: $4,000 for a 35 sq. ft. laundry bump-out, about $114 per foot, our arithmetic3 — cantilevering off the existing foundation skips foundation work and keeps per-foot costs low (HomeGuide).2
Example 3 — full budget on the average job. Fixr’s $65,000 average + architect plans ($1,200 to $5,000) + permits ($150 to $7,500) + site prep ($1,500 to $5,000) = roughly $68,000 to $82,500 all-in, our arithmetic.123 The line items outside the contractor quote add 5 to 25%.
FAQ
Build out or build up? Out is far cheaper: $80 to $250 per sq. ft. versus $200 to $500+ up, because a second story requires foundation, wall, and roof modifications (Angi, HomeGuide).12
What is the cheapest addition? A cantilevered bump-out — from $4,000 for a laundry room (Fixr). No new foundation means the lowest per-foot cost.23
What drives cost most? Plumbing and structure. Bathrooms and kitchens outprice bedrooms per foot, and any addition needing foundation or roof work jumps a tier (Fixr, HomeGuide).23
Do I need an architect? For most additions, yes — plans are required for permits. Budget $1,200 to $5,000 (HomeGuide); complex or structural projects run higher (Angi).12
How much are permits? $150 to $7,500 depending on municipality and project size (Angi) — ask who pulls them and whether the fee is in the quote.1
Sources
- Angi, How Much Does a Home Addition Cost? (2026 data).
- HomeGuide, How Much Does a Home Addition Cost? (2026).
- Fixr, How Much Does It Cost to Add New Space to a Home? (2026 data).
Related guides
Basement Finishing Cost
Kitchen Remodel Cost
Bathroom Remodel Cost
Square Footage Calculator
All cost guides