Home Addition Cost Calculator
Estimate the total cost of building a home addition including foundation, framing, roofing, and interior finishes.
Results
Visualization
How It Works
A home addition is one of the most significant remodeling investments, typically costing $150-$400 per square foot depending on finish quality. The total cost includes foundation, structural framing, roofing, electrical, plumbing, and interior finishing work.
The Formula
Variables
- Foundation — Slab $15/sqft, crawl space $25/sqft, basement $55/sqft
- Framing/Roof — Structural framing and roof extension at ~$45/sqft, 1.25x for 2-story
- Interior Finishes — Basic $40/sqft, mid-range $75/sqft, high-end $140/sqft
- Plumbing — Base $8,500 + $12/sqft if bathroom included
- Permits/Architectural — Permits ~$3.50/sqft, architectural plans $1,500-$3,500
Worked Example
For a 400 sq ft single-story slab addition with mid-range finishes and a bathroom: Foundation $6,000 + Framing $18,000 + Electrical $6,000 + Plumbing $13,300 + Interior $30,000 + Permits $4,900. Total = $78,200 (~$196/sqft).
Practical Tips
- Second-story additions cost 20-30% more than ground-level due to structural reinforcement
- Get a structural engineer assessment before starting any addition project
- Adding a bathroom increases cost significantly but also increases home value the most
- Factor in 15-20% contingency budget for unexpected issues found during construction
- Check local zoning setback requirements before planning your addition size and location
Frequently Asked Questions
How long does a home addition take?
A typical single-story addition takes 3-6 months from permits to completion. Second-story additions can take 4-8 months.
Do I need an architect?
For additions over 200 sq ft, most municipalities require stamped architectural plans. Even for smaller additions, professional plans help avoid costly mistakes.
What is the ROI on a home addition?
Home additions typically recoup 50-70% of their cost at resale. Bathroom additions and family rooms have the highest ROI.
Can I live in my home during construction?
Usually yes for ground-floor additions. Second-story additions may require temporary relocation due to roof removal and structural work.
Is it cheaper to add on or move?
Generally, if you need less than 500 sq ft, an addition is cheaper. For larger space needs, moving may be more economical when you factor in real estate transaction costs.