Typical addition: 200-600 sq ft
Enter the addition square footage to see a detailed cost estimate.
Room Addition Cost Guide
Per-square-foot costs, alternatives to additions, and permit requirements.
How Much Does a Room Addition Cost in 2026?
Room additions cost $150–$400+ per square foot, making them one of the most expensive home improvement projects.
- Basic room (bedroom/family room): $150–$250/sq ft
- Room with bathroom: $200–$350/sq ft (plumbing adds significant cost)
- Sunroom/4-season room: $100–$250/sq ft
- Second story addition: $200–$400+/sq ft (structural reinforcement needed)
- Average 12×16 bedroom addition (192 sq ft): $30,000–$60,000
Room additions are essentially new construction tied to existing structure — expect per-SF costs similar to or higher than new home building.
Key Takeaways
- Basic room addition: $150–$250/sq ft
- 12×16 bedroom: $30,000–$60,000
- Second story: $200–$400+/sq ft
Room Addition vs. Finishing Existing Space
Finishing a basement or attic costs 40–60% less than building an addition because the shell (foundation, walls, roof) already exists.
- Basement finish: $25–$75/sq ft (foundation already exists)
- Attic conversion: $50–$150/sq ft (may need dormers, stairs, structural)
- Garage conversion: $40–$100/sq ft (shell exists, needs finishing)
- New room addition: $150–$350/sq ft (all new construction)
Before building out, always evaluate existing unused space first. The cost savings are substantial and permits are often simpler.
Key Takeaways
- Basement finish: 40–60% cheaper than addition
- Garage conversion: $40–$100/sq ft
- Always evaluate unused space before adding on
Room Addition Permits & Zoning Requirements
Room additions require a building permit and must comply with setback, lot coverage, and height restrictions.
- Permit cost: $1,000–$5,000 (based on project value)
- Architectural plans: $2,000–$10,000 (required for permit)
- Structural engineering: $1,500–$5,000 (especially for second stories)
- Setback requirements: Typically 5–15 ft from property lines
- Lot coverage limits: Many zones cap building coverage at 30–50% of lot area
Check zoning before design. Some lots physically can't support additions due to setback and coverage restrictions.
Key Takeaways
- Building permit: $1,000–$5,000
- Architectural plans required: $2,000–$10,000
- Check setbacks and lot coverage before design
How to Use This Calculator
Enter Addition Square Footage
Input the total square footage for your planned addition. Typical room additions range from 200 to 600 square feet.
Select Room Type
Choose bedroom, family room, sunroom, master suite, or in-law suite. Each room type has different cost ranges based on complexity and whether plumbing is needed.
Choose Foundation and Quality
Select your foundation type (slab $5-$8/sf, crawlspace $7-$12/sf, or basement $15-$25/sf) and quality level (standard or premium finishes).
Review Cost Breakdown
See an itemized breakdown covering foundation, framing, roofing, windows, electrical, plumbing, HVAC, and interior finishes with low-to-high ranges.
Room Addition Cost Formula
Total = Square Footage x Cost per SF (varies by room type and quality)Where:
- Bedroom/Family
- = $150-$250/sf standard, $250-$400/sf premium
- Sunroom
- = $100-$200/sf standard, $200-$350/sf premium
- Master Suite
- = $200-$350/sf standard, $350-$500/sf premium
- Foundation
- = Slab $5-$8/sf, Crawlspace $7-$12/sf, Basement $15-$25/sf
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Frequently Asked Questions
How much does a room addition cost per square foot?
Room additions typically cost $100 to $500 per square foot in 2026, depending on the room type and quality. Sunrooms are the most affordable at $100-$200/sf standard. Bedrooms and family rooms run $150-$250/sf standard. Master suites and in-law suites with bathrooms cost $200-$350/sf standard and $350-$500/sf premium.
Is a room addition cheaper than buying a bigger house?
In most markets, a room addition is significantly cheaper than moving. The average room addition costs $40,000-$125,000, while moving to a larger home involves realtor commissions (5-6%), closing costs (2-3%), moving expenses, and potentially higher mortgage rates. However, if you need more than 500+ square feet, compare the total cost carefully.
How long does a room addition take to build?
A typical room addition takes 3 to 6 months from permit approval to final inspection. Simple single-story additions (bedroom, sunroom) take 8-12 weeks of construction. Master suites and in-law suites with bathrooms take 12-20 weeks. Add 4-8 weeks for architectural plans, engineering, and permit approval.
What foundation type is best for a room addition?
A concrete slab ($5-$8/sf) is the most affordable and fastest to install. A crawlspace ($7-$12/sf) works well when matching an existing crawlspace home and provides access to plumbing below. A full basement ($15-$25/sf) costs the most but adds usable space. Match your existing foundation type when possible for a cleaner connection.
What permits do I need for a room addition?
Room additions typically require a building permit, structural engineering review, and architectural plans. Most jurisdictions also require separate permits for electrical, plumbing, and mechanical (HVAC) work. Permit costs vary by location, typically $1,000-$5,000. Your contractor usually handles the permit process.
Does a room addition add value to my home?
Room additions typically return 50-65% of their cost at resale, depending on the type and your market. Master suites and in-law suites tend to have the best ROI because they add bedrooms and bathrooms to the listing. Sunrooms and family rooms add lifestyle value but return less. Always ensure the addition does not over-improve for your neighborhood.
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