Home Addition Cost in St. Louis (2026): Average Price & Estimate

Home Addition Cost in St. Louis

Estimated home addition cost in St. Louis

$38,400–$115,200

Roughly about 4% below the national average.

An affordable labor market keeps prices near or below average.

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Addition size (square feet)

Addition type

Finish level

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Based on St. Louis, MO pricing.

Estimated cost range

$38,400–$115,200

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An estimate for planning, not a quote. Get written quotes from local pros below.

Estimate, not a quote. Local prices vary by contractor and project. These are 2026 estimates for St. Louis, MO. Get written quotes from licensed St. Louis contractors before you budget.

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What to know about home addition in St. Louis

Frost heave and freeze-thaw in St. Louis can stress foundations, so good drainage and proper footing depth matter for a lasting result.

What affects home addition cost in St. Louis

Beyond the local market, the same factors that drive home addition cost everywhere apply in St. Louis:

Addition size in square feet.
Type: a bump-out is cheapest, a second-story addition the most expensive.
Whether it includes a kitchen or bathroom (plumbing).
Foundation, framing, roof, and tie-in to the existing structure.

Home Addition cost by addition type in St. Louis

These figures are adjusted for St. Louis pricing (about 0.96x the national average), so they reflect what local homeowners actually pay.

Estimated home addition cost by addition type in St. Louis (2026)

Addition type	Cost in St. Louis	Typical total
Bump-out (a few feet)	$76.80 to $230 /sq ft	About $30,700 to $92,200
Sunroom	$86.40 to $259 /sq ft	About $34,600 to $103,700
Single room addition	$96 to $288 /sq ft	About $38,400 to $115,200
In-law / suite with bath	$115 to $346 /sq ft	About $46,100 to $138,200
Second-story addition	$134 to $403 /sq ft	About $53,800 to $161,300

Frequently asked questions

How much does home addition cost in St. Louis?

In St. Louis, MO, home addition typically costs $38,400 to $115,200 in 2026 for a standard project, about 4% below the national average. Your exact price depends on size, materials, and scope.

Why does home addition cost more or less in St. Louis?

An affordable labor market keeps prices near or below average. Labor rates, permit costs, and local demand are the main reasons St. Louis prices differ from the national average.

Do I need a permit for home addition in St. Louis?

Most home addition projects require a permit. Requirements vary by city and Missouri jurisdiction, so confirm with your local building department. A licensed contractor usually pulls the permit for you.

When is the best time of year for home addition in St. Louis?

In St. Louis, exterior work is easiest from late spring through early fall. Winter weather can delay roofing, siding, concrete, and foundation jobs, and some crews book up fast once the weather breaks.

Is home addition cheaper outside St. Louis?

Sometimes. St. Louis runs about 4% below the national average. Nearby smaller towns with lower labor costs can come in cheaper, while denser urban areas often cost more. Always compare quotes from contractors who serve your specific area.