How Much Does a Home Addition Cost in Michigan?
National cost guides put a home addition at roughly $80 to $210 per square foot. One major cost guide, updated in June 2026, lists a normal range of about $21,900 to $83,400. It puts the average job near $51,000. A second story costs more, at $100 to $300 per square foot.
Those are market numbers, not our price list. What your job costs in the Bay City area comes down to the foundation, the roof tie-in, the finishes and how much of the old house changes. We give free estimates on room additions and second story additions across the Great Lakes Bay Region. Call or text (501) 520-1783.
What does an addition cost per square foot?
Price per square foot is the fastest way to get a rough number. National cost guides land in a wide band because a bump-out and a second story are different jobs.
| Type of addition | Published cost per square foot |
|---|---|
| Ground floor room addition | $80 to $210 |
| Second story addition | $100 to $300 |
| Basic attached garage | about $30 to $50 |
Small additions cost more per foot than big ones. A 100 square foot bump-out still needs footings, a roof and a wall opening. Spreading that setup over 400 square feet brings the per foot number down.
What does each type of addition cost?
Here is what the national guides publish by addition type. The sizes are typical, not fixed.
| Addition | Typical published range |
|---|---|
| Room addition, about 20 by 20 feet | $32,000 to $80,000 |
| Bump-out off a kitchen or bathroom | $4,000 to $30,000 |
| Sunroom | $25,000 to $80,000 |
| Attached garage | $25,000 to $50,000 |
| Second story addition | $100,000 to $250,000 |
A sunroom swings widely because a three season room and a heated four season room are built differently. Heat and insulation push a sunroom toward the top of that range. A separate garage cost guide lists a two car garage at $15,000 to $40,000.
Why does the foundation cost so much here?
Michigan’s residential code sets a hard number. Section R403.1.4 reads that all exterior footings and foundation systems shall extend 42 inches below actual grade. That is deeper than much of the country digs. It is one reason a Michigan addition starts higher than a national average.
The ground around Bay City is old lake plain. The soil is heavy clay, it holds water and it drains slowly. Wet clay is slower to dig, and it changes how the hole gets backfilled. National guides put excavation and site prep at $1,500 to $5,800. A basement under the addition pushes that higher.
What else moves the number?
The roof tie-in is the next big driver. New rafters have to meet the old roof so water sheds off the seam. Matching the siding and trim on an older house costs more than picking all new.
Permits and inspections are real line items. National guides put addition permits at $200 to $3,000 depending on the city and the scope. Michigan also requires a dig notice before the footings go in. State law gives the utilities at least 72 hours to mark the lines. The notice cannot be filed more than 14 days ahead.
Plumbing and electrical get done by licensed trades, and we schedule them. National guides list plumbers at $45 to $150 an hour and electricians at $50 to $130 an hour. Opening a wall and closing it back up means framing and drywall work at the seam.
Is it cheaper to build out or build up?
Building out is usually cheaper, and the national guides say the same. A second story means the existing foundation and walls have to carry new weight. That gets checked before any framing starts. National guides list structural engineers at $70 to $250 an hour.
Building up does save your yard, which matters on a tight city lot. Building out needs the room outside and a new foundation at frost depth. Which one fits gets settled when we look at your house.
Does an addition beat moving?
Michigan property tax law is part of this math. Taxable value can typically rise only by the lesser of 5 percent or the inflation rate each year. That cap holds while you own the house, and additions add value on top of it. When a house sells, the cap comes off for the buyer the year after the sale.
So a bigger house bought down the road starts from an uncapped taxable value. An addition keeps your cap and adds value only for the new space. Your assessor sets that figure, so ask them before you decide. If the layout works and only the finishes feel tired, a kitchen or bathroom remodel may cost less.
Getting a real number for your house
A per square foot range gets you in the ballpark. The real price comes from your lot, your foundation, your roofline and the finishes you pick. We are licensed and insured, and we work across the Great Lakes Bay Region. Estimates are free.
See what we build on our home additions page, then call or text (501) 520-1783 to set up a visit.