Methodology record
Read how HomeScope distinguishes national references, planning ranges, local factors, and project-specific written evidence.
Read cost-range methodology →Michigan addition planning data, without a black box.
A reusable data sheet for homeowners, journalists, housing educators, and local organizations. It publishes HomeScope’s base arithmetic, worked examples, review date, and limitations in one place.
$190base low planning rate per finished sq. ft.
$390base high planning rate per finished sq. ft.
3published worked-size examples
Aug. 142026 model review date
Reusable table
Base examples before local and project adjustments.
| Example | Finished area | Base low | Base high | Arithmetic |
|---|---|---|---|---|
| Small room addition | 200 sq. ft. | $38,000 | $78,000 | 200 × $190–$390 |
| Primary-suite scale | 400 sq. ft. | $76,000 | $156,000 | 400 × $190–$390 |
| Multi-room addition | 700 sq. ft. | $133,000 | $273,000 | 700 × $190–$390 |
Do not present these values as quotes or statewide averages. They are transparent first-pass planning outputs. Local labor, design, foundation, structural tie-ins, utilities, site work, permits, finishes, financing, concealed conditions, schedule, and contractor scope can materially change written proposals.
Method
How the model works.
The downloadable file intentionally stays small and legible. It gives another researcher enough information to reproduce the base arithmetic without implying project-specific accuracy.
- Define finished addition area. Use addition floor area—not the existing home’s size.
- Apply the published base range. Multiply finished square feet by $190 and $390.
- Keep local adjustments separate. Community factors in the interactive calculator are directional planning modifiers, not measured bids.
- Write the complete scope. Design, foundation, structure, utilities, permits, finishes, allowances, exclusions, and site work must be defined.
- Replace the model with evidence. Comparable written local proposals control the project decision.
Sources & citation
Trace the number to its published context.
Complete homeowner guide
See project drivers, permit questions, bid scope, worked examples, and the interactive local planning model.
Open the addition guide →Suggested attribution: HomeScope Guide, “Michigan Home Addition Planning Data,” version 2026.08.14, accessed on your publication date. Link to this page so readers can see the current methodology and corrections. Source-backed corrections are welcome through the corrections process.