Home Addition Cost Calculator

The calculator begins with the proposed new conditioned square footage and a broad per-square-foot planning range. Your addition type, foundation or build position, finish level, site access, utility work, design readiness, community selection, and reserve then adjust that starting point.

The displayed range is intentionally wider than a contractor quote. Early planning rarely answers every structural, site, utility, product, and approval question. Use the visible math to identify which assumptions still need evidence - not to predict an invoice.

A second story, kitchen, or primary-suite addition can require more structural work, plumbing, electrical service, ventilation, waterproofing, fixtures, and finish coordination than a straightforward conditioned room. Difficult access, complex tie-ins, utility extensions, premium selections, incomplete design, and unresolved site conditions can also increase cost or uncertainty.

A larger addition does not automatically mean every cost rises at the same rate. Design, mobilization, approvals, temporary protection, and some utility work may remain meaningful even for a small addition. That is why the tool compares project types and shows the assumptions instead of presenting one statewide price.

Before comparing proposals, ask whether each one addresses the same major categories: site and foundation; structure and exterior; utilities and interiors; and design, permits, and owner-side costs. Then review allowances, exclusions, alternates, payment milestones, change-order rules, schedule expectations, warranty, inspections, cleanup, and closeout records.

The example allocation on this page divides one range into four discussion buckets. Those percentages are not four added fees and are not a required contractor pricing format. They are prompts for finding missing scope before a low number becomes an expensive surprise.

The responsible city, village, township, county, or delegated authority depends on the property. That authority determines the applicable application path, drawings, zoning review, building and trade permits, plan review, fees, inspections, and final approvals. A mailing address alone may not identify the correct office.

Start with HomeScope’s Michigan permit directory ↗, then confirm the property and proposed scope with the official authority. The calculator does not decide whether a permit is required or whether the addition is feasible.