ADU Construction in St. Louis, MO
Global Home Views connects homeowners in St. Louis, MO with accessory dwelling units, garage conversions and in-law suites contractors through one national line. Accessory dwelling units built to code - detached builds, garage conversions and basement suites - from feasibility and zoning through final occupancy. St. Louis has a mixed housing stock: 43% detached houses, 4% attached or townhouse units and 26% in buildings of five or more units.
- Licensed and insured contractors only
- Written scope before work starts
- No obligation on quotes
- Local permit knowledge
ADU Construction cost in St. Louis
Typical St. Louis range: $69,700 - $254,200 per unit. Reflects Missouri labor and material costs. Estimate for planning, not a quote - call (844) 624-3161 for a written scope.
An ADU is a zoning project before it is a construction project. Setbacks, lot coverage, parking relief, owner-occupancy rules and utility capacity decide what can legally go on your lot, and they vary street by street.
Freeze-thaw cycling is the governing condition. Water that gets into masonry, grout or a roof detail expands when it freezes and widens the gap it entered through.
Utilities are the line item that surprises people: whether your existing panel and sewer lateral can carry a second dwelling, or whether you are trenching to the main.
What the job includes
- Zoning and feasibility review
- Plan sets and permit submittal
- Detached, attached and garage conversions
- Separate utility metering
- Kitchen and bath rough-in
- Final inspection and occupancy sign-off
Homes in St. Louis and adu construction work
Public figures for the city of St. Louis in St. Louis city, not the metro, and the general practice that follows.
St. Louis has a mixed housing stock: 43% detached houses, 4% attached or townhouse units and 26% in buildings of five or more units.1 On a mixed stock, feasibility turns on the individual lot - detached houses on larger parcels are the usual candidates; attached homes rarely qualify. Building permits in St. Louis are normally issued by the city, which is not part of a county.2,3 ADU plan review and permits go through the city building department; the contractor prepares the plan set and submits it.
Owners and renters are roughly balanced in St. Louis, with 45% of occupied homes owner-occupied (68% statewide).1 Where most occupied homes are rented, ADU inquiries often come from owners of rental property; the feasibility review is the same. The stock is old by national standards: 86% of St. Louis's housing units were built before 1980 (U.S. 50%), and only 4% since 2010.1 Older lots often have existing detached garages, the usual candidate for a conversion; the slab height and moisture barrier decide the real scope.
St. Louis sits in IECC climate zone 4A (Mixed-Humid).4 In this climate zone the energy code sets wall and ceiling insulation levels that a conversion must meet. The median owner-occupied home in St. Louis is valued at $197,500 (ACS), below the Missouri median of $230,300.1 With values below the state median, phased scopes - the essential work first - are a common way to keep a project sensible.
Heating dominates the year: about 4,433 heating degree days against 1,713 cooling degree days (base 65°F).5,6 In a heating-led climate, insulation and air sealing carry most of the energy-code weight for any work that opens the envelope.
| Before 1940 | 57.9% |
|---|---|
| 1940-1959 | 17.6% |
| 1960-1979 | 10.7% |
| 1980-1999 | 6.1% |
| 2000-2009 | 4% |
| 2010 or later | 3.7% |
Sources and notes (6)
- U.S. Census Bureau, American Community Survey 5-year estimates (ACS 2020-2024 5-year (released 2026-01))
- U.S. Census Bureau population estimates (Vintage 2024)
- U.S. Census Bureau geographic code files (2020)
- Guide to Determining Climate Zones by County: Building America and IECC 2021 Updates (PNNL-33270) (September 2022 (IECC 2021 county map))
- NOAA NCEI U.S. Climate Normals, nearest station (1991-2020 normals (published 2021))
- NOAA NCEI normals station inventory (1991-2020)
- Climate figures are for NOAA station St Louis Lambert Intl Ap, 10.7 miles from the place center; housing figures are ACS ACS 2020-2024 5-year with 90% margins of error in the source tables.
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St. Louis and nearby
Requests for St. Louis go through our national line, (844) 624-3161; we confirm whether a contractor can take the job. How a referral works.
ADU Construction nearby
Straight-line distances between place centers, not drive times. All ADU Construction in Missouri
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Open St. Louis, MO in Google MapsADU Construction questions in St. Louis
How much does adu construction cost in St. Louis, MO?
Most adu construction projects in St. Louis, MO land between $69,700 and $254,200, depending on scope, access and material grade. That is an estimated range for planning, not a quote - call (844) 624-3161 and we will scope your job properly.
Can I legally build an ADU on my lot?
That depends on your zoning, setbacks, lot coverage and utility capacity. Feasibility review comes first, before any design spend.
What kind of housing does St. Louis have?
St. Louis has a mixed housing stock: 43% detached houses, 4% attached or townhouse units and 26% in buildings of five or more units. Owners and renters are roughly balanced in St. Louis, with 45% of occupied homes owner-occupied (68% statewide). Census figures for the place itself, not the metro.
Who issues building permits in St. Louis?
Building permits in St. Louis are normally issued by the city, which is not part of a county. Whether a specific job needs one is decided by that office; the contractor confirms it before work starts.
Other services in St. Louis
Get a free St. Louis ADU Construction quote
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