Build housing with the unknowns visible.

Why a single cost-per-square-foot number isn't a budget

A build budget is really four categories stacked together: hard costs (the physical structure), soft costs (design, permits, engineering, financing), site work (grading, utilities, access), and contingency for the unknowns that show up once ground actually breaks. A generic per-square-foot figure — the number most people start with — quietly assumes average conditions for all four, and average conditions on a specific lot are the exception, not the rule.

What most commonly blows past a per-square-foot estimate

• Site conditions — slope, soil, drainage, and utility access — that a flat rate never priced in for your specific lot.
• Financing costs and delays, which extend carrying costs the longer a project runs.
• Code and inspection requirements that vary by jurisdiction and can add scope mid-project.
• A contingency line set too low, or skipped, "just this once."

For how to build a full budget with each of these visible rather than buried in one number, see build cost assumptions: why "cost per square foot" isn't a budget. If an accessory dwelling unit specifically is the project, NationwideADU is the dedicated resource for that.