Home Addition Calculator
Calculate the cost of any home addition — bedroom, bathroom, family room, sunroom, second story, or bump-out. Compare addition cost vs. buying a larger home and see your true ROI.
Compare all addition types by cost, timeline, complexity, and ROI. Mid-range quality assumed.
| Addition Type | Typical Cost | Cost/Sq Ft | ROI | Timeline | Complexity |
|---|---|---|---|---|---|
| Bedroom Addition ✓ | $25,200–$50,400 | $80–$200/sq ft | 57% | 8–12 weeks | Moderate |
| Bathroom Addition | $12,600–$25,200 | $200–$450/sq ft | 54% | 4–8 weeks | Moderate–High |
| Family Room / Great Room | $31,500–$63,000 | $100–$250/sq ft | 55% | 10–16 weeks | Moderate |
| Sunroom / Four-Season Room | $27,300–$54,600 | $80–$220/sq ft | 50% | 6–10 weeks | Low–Moderate |
| Second Story Addition | $126,000–$252,000 | $150–$350/sq ft | 65% | 16–24 weeks | Very High |
| Bump-Out / Micro-Addition | $11,200–$22,400 | $100–$280/sq ft | 53% | 4–8 weeks | Moderate |
Before hiring an architect, verify your local zoning allows the addition you want. These rules determine the maximum size of any addition.
- Front setback: typically 20–30 ft from street (no additions toward front)
- Rear setback: typically 10–25 ft (limits how far you can extend into backyard)
- Side setbacks: typically 5–10 ft (limits second-story extensions)
- Corner lots have additional street-side setbacks
- Check with your county/city planning department — these vary significantly
- Most residential zones cap total building coverage at 30–50% of lot area
- Includes house, garage, detached structures, covered decks
- Calculate: (house sqft + addition sqft + garage) ÷ lot sqft = coverage %
- If near the limit, addition may not be permissible
- Second-story additions don't increase footprint — avoid coverage issues
- FAR = Total built area ÷ Lot area
- Typical residential FAR: 0.4–1.0 (varies widely)
- A 7,500 sq ft lot with FAR 0.5 allows 3,750 sq ft of building
- Second-story additions count against FAR
- FAR is strictly enforced in many suburbs and urban areas
- Most residential zones cap building height at 25–35 feet
- Measured from average grade to highest point of roof
- Second-story additions are often the main height constraint
- HOA rules may be stricter than zoning — check both
How to Use This Home Addition Calculator
Select your addition type, enter the square footage and construction quality to instantly see total cost, per-square-foot cost, and estimated ROI at resale.
Quick Calculator
Choose the Addition Type that matches your project. Enter the Addition Size in square feet — typical ranges: bedroom 150–250 sq ft, bathroom 40–100 sq ft, family room 300–500 sq ft, second story 500–1,500 sq ft. Choose Construction Quality: Standard uses builder-grade materials; Mid-Range matches your existing home quality; Premium uses custom finishes. Enter your home value to see ROI in context.
Advanced: Types Comparison, Cost Breakdown, vs. Moving
Addition Types compares all six types by cost range, ROI, timeline, and complexity. Cost Breakdown shows how your total cost splits across foundation, framing, roofing, MEP, finishes, permits, and contingency. vs. Moving calculates whether adding on or selling and buying a larger home is cheaper — accounting for real estate commissions, closing costs, and moving expenses.
Pro: Zoning Check, Permit Timeline, Value Per Sq Ft
Zoning Check explains setbacks, lot coverage limits, FAR ratio, and height restrictions that determine the maximum size addition you can build. Permit Timeline walks through the full 4–9 month project lifecycle from design to move-in. Value Per Sq Ft explains why added square footage is appraised at 50–65% of your existing home's $/sq ft, and how to maximize your addition's value.
Home Addition Cost Formula
Cost Per Sq Ft by Type:
• Bedroom: $80–$200/sq ft
• Bathroom: $200–$450/sq ft
• Family Room: $100–$250/sq ft
• Sunroom: $80–$220/sq ft
• Second Story: $150–$350/sq ft
• Bump-Out: $100–$280/sq ft
Cost Breakdown:
• Foundation 15% · Framing 20% · Roofing 10%
• MEP 20% · Finishes 25% · Permits + Contingency 10%
Value Added ≈ Total Cost × 50–65% (addition ROI rate)
ROI = (Value Added − Total Cost) / Total Cost × 100
Labor represents 40–60% of home addition costs. The remaining cost is materials. Regional variation is significant — additions in high-cost markets (California, New York, Seattle) can run 50–100% above Midwest and Southern averages for identical projects.
Example: Master Bedroom Addition in Austin, TX
The Williams family adds a primary bedroom suite — 250 sq ft
| Addition Type | Primary Bedroom + En Suite Bathroom |
| Size | 250 sq ft (bedroom) + 80 sq ft (bath) |
| Quality | Mid-Range |
| Bedroom Cost (250 sq ft @ $120/sq ft) | $30,000 |
| Bathroom Addition (80 sq ft @ $300/sq ft) | $24,000 |
| Total Addition Cost | $54,000 |
| Contingency (10%) | +$5,400 |
| Architect Fees | +$4,500 |
| Permits | +$1,200 |
| All-In Cost | $65,100 |
| Estimated Value Added (~55%) | $35,800 |
| vs. Buying Larger Home (transaction costs) | $45,000+ in selling/buying friction |
The Williams family chose the addition over moving because their transaction cost to sell and buy a $550K home would exceed $45,000 in commissions and closing costs — more than the "lost" ROI on the addition, and they got to stay in their neighborhood and school district.