Home Addition Cost Calculators
Free 2026 estimates for every type of home addition — room additions, garages, sunrooms, attic conversions, and basement finishing. Know your number before talking to a contractor.
Pick Your Addition Calculator
Home additions are the largest financial decisions most homeowners make. These calculators use real 2026 contractor data so you walk into every conversation fully prepared.
Home Addition Cost Calculator
Estimate a room addition or home extension by square footage, finish level, and room type.
📊 $32,000–$80,000Garage Addition Cost Calculator
Estimate attached or detached garage construction cost by size, number of bays, and finish level.
📊 $18,000–$42,000Sunroom Addition Cost Calculator
Estimate sunroom addition cost by size, construction type (three-season vs. four-season), and foundation.
📊 $15,000–$45,000Attic Conversion Cost Calculator
Estimate attic conversion cost by usable square footage, finish level, and structural requirements.
📊 $20,000–$55,000Basement Finishing Cost Calculator
Estimate basement finishing cost by square footage, finish level, and included features.
📊 $12,000–$35,000Carport Cost Calculator
Estimate carport cost by size, material, and attachment type. Covers single and double-car metal, wood, and vinyl carports with installation.
📊 Typical range: $1,500–$20,000What Affects Home Addition Cost?
Addition Type & Size
A ground-floor room addition costs $150–$300/sf for a full buildout. A second-story addition costs $180–$350/sf due to structural reinforcement of existing walls and foundation. Basement finishing costs $25–$55/sf — the most affordable way to add livable space. Attic conversions cost $40–$100/sf depending on structural changes needed.
Foundation & Structure
Every addition touching the ground needs a foundation — concrete slab, crawl space, or full basement. Foundation work accounts for 10–20% of total addition cost. Second-story additions require engineering assessment of existing foundation and wall capacity. Structural costs are the most unpredictable line item in addition projects.
Finish Level & Features
A basic addition (drywall, standard flooring, single bathroom) costs $150–$200/sf. A mid-range finish with hardwood floors, custom trim, and a full bath runs $200–$280/sf. A luxury finish with high-end everything exceeds $300/sf. Kitchen and bathroom additions cost more per square foot than bedrooms or living rooms due to plumbing and electrical complexity.
Permits, Architecture & Engineering
Building permits for additions run $500–$3,000 depending on scope and municipality. Architectural drawings cost $3,000–$8,000 for a typical addition. Structural engineering adds $1,500–$4,000. These fees are non-negotiable — they protect your investment by ensuring the addition is built to code and is insurable.