Home / Additions
House addition cost calculator
What it costs to add a room, suite, sunroom or second story in your state, and how much of that a buyer will pay back.
What drives addition cost
- Foundation and roof. Every addition needs both, which is why the per-foot price is high even for a plain room.
- Plumbing. A bathroom or kitchen in the addition is the biggest multiplier.
- Tie-in. Matching rooflines, siding and floors to the existing house takes skilled labor.
- Soft costs. Architect, engineer, survey and permits typically add 10–15%.
Cheaper ways to gain space
Finishing a basement costs a fraction per foot and recoups a larger share. Converting a garage or attic is another option where zoning allows. See the primary suite addition and bathroom addition ROI pages for detail.
Frequently asked questions
How much does a house addition cost?
Most ground-floor additions cost roughly $200–$400 per square foot nationally, more for kitchens and bathrooms and in expensive regions. A 400 sq ft bedroom-and-bath addition often lands between $100,000 and $180,000.
Is it cheaper to build up or out?
Building out is usually cheaper per square foot when you have yard space, because a second story requires reinforcing the existing structure and temporarily removing the roof.
Does an addition add value?
Additions add usable space, but typically recoup well under their cost, commonly a third to a half. Finishing an existing basement or attic returns more.
Do I need a permit for an addition?
Yes. Additions need building permits and usually zoning review for setbacks, height and lot coverage. Check before paying for full plans.