Build a preliminary home-addition budget from construction cost per square foot plus design, permits, site conditions, and contingency. The result shows the all-in planning total, reserve amount, and effective cost per square foot so you can test scope before requesting detailed bids.
The total is a feasibility budget, not a bid. It makes allowances visible so a low base cost does not hide design, permitting, site, or uncertainty costs.
Actual costs vary by location, structure, utilities, finishes, code requirements, market conditions, and procurement method.
For 400 sq ft at $275/sq ft, 10% design, $8,000 permits, 8% site premium, and 15% contingency:
It provides a transparent planning allowance; replace it with a fixed proposal when professional fees are known.
No. The result is a project budget before loan interest and carrying costs.
Include known fixed upgrades in permits and fixed fees, or incorporate uncertain work in the site premium.
Yes. This model applies contingency to the full pre-contingency subtotal.
Yes, if you divide a comparable construction quote by its included floor area and understand what the quote excludes.
| Budget layer | Calculation base |
|---|---|
| Base construction | Area × base rate |
| Site premium | Base construction |
| Design/engineering | Base construction |
| Permits and fees | Fixed input |
| Contingency | Full subtotal |