Single Storey Extension Cost 2026
A single-storey extension — a ground-level addition that builds out from your home — typically costs between $22,000 and $90,000, with the average project around $51,000.
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Key takeaways
Building out at ground level usually costs $150–$350 per square foot, so a modest room addition starts around $22,000 and a larger or higher-finish extension can reach $90,000 or more, with the national average near $51,000. Basic build-outs like a bedroom or sunroom sit at the lower end ($150–$200/sq ft); kitchens and bathrooms cost much more ($250–$500+/sq ft) because of plumbing, fixtures, and waterproofing. Foundation work, roof tie-ins, finishes, and local labor rates are the main cost drivers.
Average single storey extension cost in the US
A single-storey extension is a ground-level home addition that expands your floor plan outward, such as a new family room, bedroom, or kitchen extension.
National average, per project · adjusted to your area when you enter a ZIP code
Benchmark is for a standard ground-level build-out; kitchen or bathroom extensions and high-end finishes cost more.
What affects the cost
Several factors influence the price you’re quoted for single storey extension:
- Size & layout. Total cost scales with square footage; complex layouts and rooflines cost more.
- Room type. Bedrooms and family rooms are cheaper per square foot; kitchens and bathrooms are far more expensive due to plumbing and fixtures.
- Finish level. Basic finishes run $150–$200/sq ft; mid-range and high-end finishes push well above $275/sq ft.
- Foundation & roof tie-in. Matching the new foundation and roof to the existing home adds structural work.
- Permits & local labor. Permit fees and regional labor rates vary widely and are reflected in the local estimate.
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Building out vs. building up
A single-storey (build-out) extension is generally cheaper than adding a second storey, which runs $300–$500 per square foot because of structural reinforcement. Build-outs do require available lot space and may trigger setback or zoning rules.
How to budget accurately
Get a detailed scope from a design-build contractor, set aside 10–20% contingency for surprises, and confirm whether the price includes permits, design, and finishes. Square-foot pricing is a starting point — your final cost depends on finishes and site conditions.
Frequently asked questions
Ground-level build-outs typically run $150–$350 per square foot. Basic finishes are $150–$200, mid-range around $200–$275, and kitchens or bathrooms can reach $250–$500+ per square foot.
The national average is roughly $51,000, with most projects between about $22,000 and $83,000 depending on size, room type, and finish level.
Labor, materials, and permit costs vary by region. This tool adjusts the national benchmark by your area's cost-of-living index.
Check single storey extension costs in your area
Enter your ZIP code for a cost-of-living adjusted estimate near you.
Cost figures on this page are cost-of-living adjusted estimates for informational purposes only and are not a quote. Always get written quotes from licensed local pros for your specific single storey extension project. See how we estimate costs.