ADU Construction cost per square foot in St. Louis
ADU Construction cost per square foot in St. Louis, Missouri in 2026.
Low
$141,000
Average
$211,500
High
$282,000
St. Louis crews quote about $235 – $470 per square foot.
Multiply local unit rates by your real measurements.
What drives adu construction prices in St. Louis
Local labor, permitting and climate move St. Louis prices away from the national average.
Labor market
Licensed trade labor in St. Louis runs about 94% of the national average, and the best crews book out fastest in spring and early summer.
Permits
Most St. Louis, MO projects that change structure, electrical, plumbing or mechanical systems need a permit from the local building department; cosmetic work usually does not.
Climate
Missouri weather drives material choices here, so ask contractors what they install most often in St. Louis and why.
St. Louis unit pricing by material
Ways to lower your St. Louis price
- Use pre-approved ADU plans where your city offers them — saves months and design fees.
- Detach only if required; attached and conversion ADUs cost far less.
- Collect three written bids on an identical scope — spreads of 20–40% are normal.
- Book in the off-season and stay flexible on the start date to save 5–15%.
- Bundle nearby work into one mobilization so you only pay setup and travel once.
- Ask what the contractor would change to cut 10% without hurting durability.
St. Louis questions
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