Home addition planning tool
Home Addition Cost Calculator
See a transparent Michigan planning range, understand what changes it, and turn the result into one clear description for permits and contractor bids.
Not sure which city or township handles permits? Find it here (opens a new tab) ↗01 · Estimate
Price the work you can describe today.
Start with size, location, addition type, foundation, and finish. Open detailed planning only when you are ready to refine site, utility, design, and reserve assumptions.
Check what the property allows
Setbacks, lot coverage, structural tie-ins, utilities, and required plans can change the project. Local offices and qualified professionals make those decisions.
Step 2 of 2 · Describe what you know
02 · Understand the number
Three inputs create the range.
Result: $82,080–$168,480. Change a choice above and this range updates immediately.
community
A broad location adjustment used for planning. It is not a measured city price index.
- +8%
type
The room type changes structural, plumbing, ventilation, cabinet, and finish assumptions.
- No change
foundation
Building at grade, over a basement, or above an existing structure changes the structural work.
- No change
site
Access, grading, tie-ins, and utility conditions can make the same square footage harder to build.
- No change
finish
A planning allowance for practical, mid-range, or premium product and finish choices.
- No change
utilities
How far and how extensively plumbing, electrical, HVAC, and ventilation must be extended.
- No change
readiness
Early unresolved design decisions carry more uncertainty than permit-ready plans and selections.
- No change
These adjustments are visible educational assumptions. They are not local price measurements, contractor bids, or feasibility findings.
Example allocation
One estimate, split into four planning buckets.
These four percentages total 100%.
They divide the same $82,080–$168,480 range. Do not add them on top of the estimate.
To help you notice when a contractor proposal appears to omit a major part of the job.
No. Replace these example shares with actual written proposal amounts.
Ask each bidder to price the same four categories so totals are easier to compare.
Site and foundation
$14,774–$30,326See what belongs here
Access, excavation, drainage, footings, foundation, and restoration.
Structure and exterior
$34,474–$70,762See what belongs here
Framing, roof and wall tie-ins, windows, doors, insulation, and weather protection.
Utilities and interiors
$22,982–$47,174See what belongs here
Electrical, plumbing, HVAC, drywall, trim, flooring, fixtures, and finishes.
Design, permits, and owner costs
$9,850–$20,218See what belongs here
Survey, design, engineering, approvals, temporary needs, and final records.
03 · Compare addition types
See how the same 400 sq. ft. changes by scope.
Each card keeps every other assumption the same. Choosing one updates the main estimate above.
Current estimate: Single-story room addition
Single-story room addition
$82,080–$168,480New foundation, conditioned room, exterior envelope, and house tie-in.
Kitchen addition
$96,854–$198,806Adds cabinets, appliances, plumbing, power, ventilation, and finishes.
Bathroom or primary-suite addition
$100,138–$205,546Adds plumbing, ventilation, waterproofing, fixtures, and trades.
Second-story addition
$108,346–$222,394Adds reinforcement, roof work, stairs, weather protection, and disruption.
Bump-out / small extension
$91,930–$188,698Spreads design, mobilization, tie-ins, and permits over less area.
04 · Prepare the project
Give every builder the same assumptions.
This creates a plain-language project description - not a contract. Paste the same text into every bid request, then attach drawings and selections.
05 · Complete the decision pack
Turn this estimate into a buildable, comparable plan.
The range is one input. A complete addition decision also needs property feasibility, one shared scope, comparable proposals, and a durable project record.
Planning range$82,080–$168,480Working budget: $91,930–$188,698
Current project400 sq. ft. Single-story room additionTroy, Michigan
Still requires confirmationProperty + municipalityFeasibility, drawings, approvals, fees, and inspections
- 01Verify locally
Confirm what the property can support.
Find the local permit office and confirm zoning, site limits, required drawings, permits, fees, inspections, and final records.
Build the Troy permit checklist ↗ - 02Define once
Write one scope for every bidder.
Keep the same size, assumptions, allowances, alternates, exclusions, schedule expectations, warranty, and closeout requirements.
Open the shared project description ↗ - 03Compare fairly
Separate price from missing scope.
Compare the same categories, payment milestones, change-order rules, responsibilities, and records - not only the bottom-line total.
Compare bids with this requested scope ↗ - 04Keep the record
Save the plan with the home.
Keep this addition context with the property so estimates, decisions, bids, status, spending, and future artifacts stay organized.
Open my account and add this project →
Not established by this estimate: property-specific feasibility, municipal approval, structural capacity, concealed conditions, final drawings, product selections, utility upgrades, final fees, contractor availability, or schedule.
Reusable decision pack
Save or share this planning record.
The PDF includes the estimate, drivers, math, allocation, scope, permit questions, and bid checkpoints. Browser and account saves remember the project basics - not the full private worksheet.
The essentials
Your estimate, at a glance.
Use the range to plan. Confirm the details with your local permit office and written contractor bids.
Start with size. Adjust for scope.
- Square footage sets the starting range.
- Your choices adjust the planning assumptions.
- The result is a planning range, not a quote.
How the estimate works
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.
What can raise the cost?
- More structural or utility work.
- Difficult access and complex tie-ins.
- Premium finishes or unresolved design choices.
More about cost drivers
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.
Check what is included.
- Site, foundation, structure, and exterior.
- Utilities, interiors, design, and permits.
- Allowances, exclusions, payments, and final records.
More about scope and allowances
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.
Confirm the right permit office.
- Use the property address to check jurisdiction.
- Ask which drawings, permits, and inspections apply.
- Confirm requirements with the official local office.
More about local permits
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.
Your next step
Turn the range into a plan.
Common home addition calculator questions
Is cost per square foot enough to plan an addition?
No. It is a useful starting unit, but it does not describe the property, structure, utility capacity, access, products, approvals, or exact scope. Use it to establish a range, then replace assumptions with project evidence.
Why does the calculator show a range instead of one price?
A single number would hide uncertainty that has not been resolved. The range makes that uncertainty visible while you refine the addition type, site, utilities, design readiness, finishes, and reserve.
Should I give every contractor the calculator result?
Share the project description and assumptions, not only the number. Asking every bidder to price the same written scope creates a more useful comparison and makes exclusions or allowances easier to identify.
Does selecting a Michigan location create a local quote?
No. Your city or township connects the project to the right planning and permit starting point. The factors remain educational assumptions and are not measured local bids, contractor pricing, or an approval decision.
What should I do after using the calculator?
Find the local permit office, investigate what the property can support, define one written scope, obtain comparable proposals, review payment and change terms, and keep decisions and final records with the home.
Permit starting point
Where do I check home addition permit requirements in Michigan?
The local office that handles permits decides which building and trade permits, zoning review, drawings, plan review, inspections, and closeout records apply to the property and exact work.
Use an official local source
HomeScope does not determine whether a permit is required. Find the local permit office and prepare your questions ↗
05 · Methodology and trust
Know what the estimate can - and cannot - tell you.
The $190–$390 base, community factors, and addition-type multipliers are transparent educational assumptions, not observed bids or a local price index.
Verify the property and written scope
Actual cost depends on design, site work, structure, utilities, products, approvals, contractor availability, and proposals. Read the complete cost methodology →