Room Addition Cost Calculator
Multiply the addition's area by your own shell and interior finish rates, add a lump-sum allowance for site work and foundations, then apply contingency and contractor markup. Rates stay yours — nothing is filled in from national averages.
Room Addition Cost Calculator
Multiply the addition's area by your own shell and interior finish rates, add a lump-sum allowance for site work and foundations, then apply contingency and contractor markup. Rates stay yours — nothing is filled in from national averages.
Method and assumptions
Figur adds up only the allowances, quantities, and rates you enter, applies your contingency percentage to the subtotal, and adds contractor markup last. Everything is calculated locally in your browser.
- Every cost comes from you: the calculator does not fill in national averages or present them as guaranteed local prices.
- Contingency applies to your base costs and markup to the adjusted subtotal, in exactly the order shown in the breakdown.
- Permits, design fees, local taxes, and structural work are excluded unless you fold them into an allowance.
- Real prices depend on your market, season, site access, and hidden conditions that only appear during the work.
This tool produces a planning budget, not a binding quote or construction, legal, or financial advice. Get real local quotes before committing money.
Sources and references
No external data source is required: the budget uses only the quantities, allowances, and percentages you enter.
Frequently asked questions
What splits the shell rate from the finish rate?
The shell usually means foundation-up framing, roofing, windows, siding, and weatherproofing; finish covers drywall, flooring, trim, paint, and fixtures. Splitting them shows where the money concentrates.
What costs hide in additions?
Excavation surprises, utility relocations, tying the new roof into the old one, and matching existing finishes. Design fees and permits also sit outside most per-square-foot rates, so budget them separately.