How much does a room addition cost per square foot?

Room additions cost $80-$250 per square foot in 2025, depending on the room type and finishes. A basic bedroom addition runs $80-$150/sq ft, a bathroom addition $150-$250/sq ft, and a family room $100-$200/sq ft. Second-story additions cost 20-30% more than ground-floor.

Is it cheaper to add on or build up?

Building up (second story) costs 10-30% more per square foot than building out due to structural reinforcement of existing walls and foundation. However, building up preserves yard space and avoids new foundation costs. The best choice depends on your existing foundation capacity and lot size.

How long does a room addition take to build?

A standard room addition takes 2-4 months from permit to completion. This includes 2-4 weeks for foundation, 2-3 weeks for framing and roofing, 2-3 weeks for mechanical (plumbing, electrical, HVAC), and 3-4 weeks for finishing. Permit approval adds 2-6 weeks.

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Assumptions & Sources

Assumptions

Foundation costs: Based on typical residential foundation requirements for your region.
Story multiplier: Second story additions cost 35% more due to structural requirements.
Finish level: Basic (builder-grade), Standard (mid-range), Premium (high-end), Luxury (custom).
Timeline: Based on typical crew size and permit processing times.
Permits: Assumes standard residential permit fees in your area.

Data Sources

RSMeans Construction Cost Data 2025
HomeAdvisor True Cost Guide 2024-2025
Remodeling Magazine Cost vs. Value Report 2024-2025
National Association of Home Builders (NAHB)

Last updated: February 2026

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