Home Addition Cost Estimator
Enter the addition size and type for a realistic construction budget.
Runs entirely in your browser — your numbers never leave this page.
How it works
Addition cost = size × type rate × finish:
- Bump-out (~$200/sq ft): extending an existing room — new foundation, roof tie-in, systems extension.
- Primary suite (~$260/sq ft): bedroom + bath — plumbing drives the premium.
- Second story (~$230/sq ft): no new foundation, but structural work and living through construction.
- Garage conversion (~$90/sq ft): cheapest — walls and roof exist. But you lose the garage, which buyers want.
- Finish multiplier: basic 0.8x, high-end 1.5x — fixtures and finishes swing the total enormously.
- ROI reality: additions return ~50–60% at resale. Build for your life, not profit.
Frequently asked questions
How much does a home addition cost?
Roughly $200/sq ft for a bump-out, $230 second-story, $260 primary suite, $90 garage conversion — mid-range finishes.
Why are additions so expensive per sq ft?
Tying into an existing structure — foundation work, roof tie-ins, systems extensions — is fiddly, custom work.
Is a second story cheaper than building out?
Often yes per sq ft (no new foundation), but structural verification and living through it add complexity.
Do I need an architect?
For structural additions, yes — and most jurisdictions require stamped plans for permits anyway.
How long does an addition take?
3–6 months for a typical room addition; second stories run 4–8 months.
Will an addition raise my property taxes?
Yes — the added square footage and value get reassessed. Budget for it.
Garage conversion: good idea?
Cheapest addition (~$90/sq ft) but you lose parking — and homes with garages appraise and sell better.
What is the ROI on additions?
About 50–60% recouped at resale. Additions are lifestyle spending, not investments.
Can I live in the house during construction?
Usually yes for bump-outs; second stories are miserable to live through. Budget for dust, noise, and utility interruptions.
What permits are needed?
Building, electrical, plumbing, and often zoning approval — add ~10% and 4–12 weeks for the process.