Find out home addition costs per square foot in 2026. Room addition, second story, and bump-out costs compared. Free home addition guide.
Home additions cost $100-$300 per square foot — making a 400 sq ft room addition cost $40,000-$120,000. Second-story additions cost the most at $150-$300 per square foot while bump-outs and garage conversions cost less. Home additions are the most expensive way to add space — but often the only option when you love your location but need more room.
Cost per square foot installed: Small bump-out (under 100 sq ft, cantilevered): $80-$150/sq ft. Single room addition (new foundation): $100-$200/sq ft. Master suite addition: $125-$250/sq ft. Garage conversion to living space: $60-$120/sq ft — lowest cost option. Second story addition (full): $150-$300/sq ft. Sunroom or enclosed porch: $80-$150/sq ft. In-law suite with separate entrance: $125-$250/sq ft. Average 400 sq ft room addition: $40,000-$80,000.
Addition ROI analysis: Family room addition: 50-60% ROI typical. Primary bedroom suite: 55-65% ROI. Bathroom addition: 50-60% ROI. Kitchen expansion: 50-60% ROI. Second story: 50-75% ROI — most valuable per dollar in high-cost markets. Worth it financially when: addition costs less than moving to larger home plus transaction costs, you love your location, local real estate supports higher square footage pricing.
Addition vs move comparison: Moving costs: real estate commission 5-6% on current home sale + closing costs 2-3% on new purchase + moving costs. On $400,000 home: $28,000-$36,000 in transaction costs. Plus premium for larger home (if comparable exists). Addition may be cheaper if: you love your location, no suitable larger homes in your area, addition cost is less than home price premium. Move may be cheaper if: needed space exceeds practical addition capacity.
Home addition timeline: Design and permitting: 2-4 months (architect drawings, permit approval). Construction: 2-6 months depending on scope. Small bump-out: 2-3 months total. Full room addition: 4-6 months. Second story: 6-12 months. Can I live in home during construction? Usually yes for additions — work is external until connecting to existing home. Expect noise, dust, and disruption for final connection phase.
Home addition permits required: Building permit: always required for structural work. Electrical permit: for any new wiring. Plumbing permit: for any new plumbing. Mechanical permit: for HVAC extension. Zoning compliance: addition must meet setback, height, and lot coverage rules. HOA approval: exterior changes require HOA sign-off in most communities. Total permit costs: $500-$3,000 depending on jurisdiction and project size. Permits protect you — unpermitted additions create legal issues at home sale.
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