Cost Estimators · Construction
Home Addition Cost Per Sq Ft Calculator
Enter your addition's square footage and instantly estimate your home extension cost.
Adding square footage to your home is one of the highest-ROI projects you can undertake — but costs vary dramatically based on what you're adding. A simple room addition costs far less per sq ft than a full second-storey or garage conversion with plumbing. Use this calculator to set a realistic budget before talking to a general contractor.
Enter an area above to see your estimate
Using national average: $100–$300/sq ft
Estimates are based on national averages and are for planning purposes only. Actual costs vary by location, contractor, and material choice.
Example: 400 sq ft addition
Area
400
sq ft
Low Estimate
$40,000
@ $100/sq ft
High Estimate
$120,000
@ $300/sq ft
Based on national average rates of $100–$300/sq ft. Actual costs will vary by location and contractor.
How much does a home addition cost per square foot?
Home additions typically cost $100–$300 per sq ft fully finished, depending on complexity. A basic room addition (bedroom, living room) runs $100–$200/sq ft. Additions requiring plumbing — bathrooms, kitchens — cost $200–$350/sq ft. Second-storey additions cost $150–$300/sq ft. Sunrooms and screened porches are cheaper at $75–$150/sq ft. Costs include foundation, framing, roofing, insulation, drywall, flooring, electrical, and finishing — but exclude furniture and high-end finishes unless specified.
Cost by project size
| Project size | Low estimate | High estimate |
|---|---|---|
| 200 sq ft (small bedroom) | $20,000 | $60,000 |
| 400 sq ft (large bedroom / office) | $40,000 | $120,000 |
| 600 sq ft (family room) | $60,000 | $180,000 |
| 800 sq ft (large addition) | $80,000 | $240,000 |
| 1,000 sq ft (full suite / garage conversion) | $100,000 | $300,000 |
Approximate 2026 US national averages at $100–$300/sq ft installed. Actual costs vary by location, contractor, and project complexity.
What affects construction cost per square foot?
Addition type
A basic bedroom or living room addition is the most affordable at $100–$200/sq ft. Adding a bathroom or kitchenette pushes costs to $200–$350/sq ft due to plumbing rough-in. Second-storey additions require structural engineering and typically cost $150–$300/sq ft.
Foundation requirements
Ground-level additions need a new foundation — either a slab ($5–$14/sq ft) or full perimeter footing. Second-storey additions avoid this cost but require structural assessment of existing walls and beams to confirm load capacity.
Electrical & HVAC extension
Extending your electrical panel and HVAC system to serve a new addition adds $3,000–$10,000+ depending on distance and existing system capacity. Upgrades to the main panel may be required if capacity is insufficient.
Windows, doors & finishes
Standard windows and doors are included in most per-sq-ft estimates. Premium windows, custom doors, vaulted ceilings, or high-end finishes can add $20–$50/sq ft to the total cost.
Permits & engineering
Home additions require building permits in virtually all jurisdictions — typically $500–$3,000. Complex additions or those in high-seismic or flood zones require engineer-stamped drawings, adding $1,500–$5,000.
Location & contractor rates
Home addition costs in major metro areas (NYC, San Francisco, Boston) run 50–100% above national averages. Always get at least 3 quotes from licensed general contractors with references for addition work.
Frequently asked questions
How much does a home addition cost per square foot?
Home additions cost $100–$300 per sq ft fully finished. A basic bedroom or family room runs $100–$200/sq ft. Additions with plumbing (bathrooms, kitchens) cost $200–$350/sq ft. Second-storey additions run $150–$300/sq ft. For a 400 sq ft addition, expect $40,000–$120,000 depending on complexity and location.
Is a home addition worth the investment?
Home additions typically return 50–80% of their cost in added home value, depending on the type and local market. Bedroom and bathroom additions in undersupplied markets often return close to 100%. The functional benefit — more living space without moving — often makes the investment worthwhile regardless of pure ROI.
How long does a home addition take to build?
A straightforward room addition takes 2–4 months from permit approval to completion. Larger or more complex additions (second storey, addition with plumbing) take 4–8 months. Permitting alone can take 4–12 weeks in many jurisdictions before construction begins.
Do I need a permit for a home addition?
Yes — virtually all home additions require a building permit. Unpermitted additions create legal and insurance problems and must be disclosed when selling. Some jurisdictions also require neighbour notification for additions that affect setbacks or easements.
What is the cheapest type of home addition?
Sunrooms, screened porches, and prefabricated additions are the most affordable at $75–$150/sq ft. Simple rectangular bedroom additions without plumbing are the next most affordable. Bump-outs (small cantilever extensions under 10 ft deep) avoid full foundation costs and can be very cost-effective for modest space additions.