St. Louis County County-adopted code, county inspection

Barndominium Builders in St. Louis County, MO

This is the county the office sits in, in Jennings, and it is also the hardest county in Missouri to buy building acreage in: the 2022 Census of Agriculture counted 222 farms on 21,936 acres here, an average holding of 99 acres, with land in farms down 52 percent in five years. What is left is at the western edge — Wildwood, which spreads 35,082 people across 66.7 square miles of land, and the Eureka fringe — where the county's own NU Non-Urban zoning sets a three-acre minimum for a dwelling and caps every detached accessory structure on the lot at 1,000 square feet put together, which is the sentence a shop-and-house buyer needs to read before anything else. For a workshop-and-home building on land that is actually for sale, the honest answer is west and north of here: Franklin, Warren, Lincoln and Jefferson counties, all inside an hour of the Page Avenue and I-44 corridors. And the second thing to know is that "St. Louis County" is not one permitting authority — 88 incorporated municipalities sit wholly or partly inside it, many of them contracting code enforcement back to the County under SLCRO § 1115.050 while keeping their own zoning approval, so the answer for a specific suburb is that suburb's answer and not the county's.

St. Louis County at a glance

County: St. Louis County
Population: 992,929
ZIP codes: 63005, 63011, 63017, 63021, 63025, 63031, 63033, 63034, 63038, 63040, 63042, 63043, 63044, 63045, 63074, 63088, 63105, 63114, 63117, 63119, 63121, 63122, 63123, 63124, 63125, 63126, 63127, 63128, 63129, 63130, 63131, 63132, 63133, 63134, 63135, 63136, 63137, 63138, 63140, 63141, 63143, 63144, 63146
Site visits: Usually the same week — the office is in Jennings, inside the county

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Building conditions in St. Louis County

Missouri sets no residential building code and no statewide way of adopting one, so the first question on any parcel is not what the code says — it is whether there is one. Only counties of the first and second classification may adopt a building code at all, and classification is set by assessed valuation rather than population, so a small county can hold the power while a much larger one does not. Zoning is a separate power with its own answer, granted only after a vote of the people and repealable by another. What changes from one jurisdiction to the next is whether the work is inspected, who issues the permit, what that office charges, how the parcel is zoned, and the design figures your drawings have to satisfy.

Build conditions for St. Louis County, drawn from the sourced facts on this page. Every figure above is cited in the quick-facts panel below, with its source and vintage.

The county's authority comes from its charter, not RSMo 64.170

St. Louis County is one of Missouri's five charter counties, and a charter county sits outside the four-class system that decides whether an ordinary Missouri county may have a building code at all. The county states the source of its own power in its own ordinance: "St. Louis County derives its zoning authority from its Charter, as authorized by Article VI, Section 18(c) of the Missouri Constitution." That is why the statute a reader will find quoted everywhere else about Missouri county codes — RSMo 64.170, which reaches only counties of the first and second classification — is the wrong citation here.

St. Louis County Revised Ordinances § 1008.010 (Floodplain Management Regulations, Findings of Fact and Purposes), read via the Municode API (productId 11512) 6 September 2026; Missouri Association of Counties, "Missouri Counties by Classification", published May 2025, CHARTER list (5 counties), PDF read 6 September 2026; Mo. Const. Art. VI, §§ 18(a) and 18(c)

The adopted residential code is the 2015 IRC

For unincorporated St. Louis County the residential code is the 2015 International Residential Code for One- and Two-Family Dwellings, including Appendix K, adopted as the Residential Code of St. Louis County. The commercial side is the 2015 International Building Code, adopted with Appendix C (Group U — Agricultural Buildings) and Appendix H. Both were enacted by the same instrument on the same day, and the residential code's administrative chapter is deleted outright and replaced by the building code's, so permits, plan review, fees, inspections and the certificate of occupancy for a house all run through the building code's Chapter 1 as the county amended it.

SLCRO §§ 1116.020 and 1115.020, both Ordinance No. 27654, adopted 18 December 2019; administrative replacement at SLCRO §§ 1116.101 and 1115.101; read via the Municode API (productId 11512) 6 September 2026

The county fills in its own design table — and here is the whole row

St. Louis County prints a completed Table R301.2(1) in the ordinance itself: ground snow load 20 lbs/ft²; wind speed V_ult 115 mph and V_asd 89 mph; topographic effects NO; special wind region NO; wind-borne debris zone NO; seismic design category C; weathering severe; frost line depth 30 inches (762 mm); termite slight to moderate; winter design temperature 2 °F; ice barrier underlayment NO; flood hazards May 24, 1985; air freezing index 1,000; mean annual temperature 55.2 °F. That 30-inch frost line is the number that sets the depth of every pier and every post hole on a post-frame building, and it is the figure to hand a foundation quote.

SLCRO § 1116.103, Table R301.2(1) (Amendments to the International Residential Code for One- and Two-Family Dwellings, 2015 edition — Chapter 3 Building Planning), Ordinance No. 27654, 18 December 2019; read via the Municode API (productId 11512) 6 September 2026

88 municipalities, and the county's answer is not theirs

88 incorporated cities, towns and villages lie wholly or partly inside St. Louis County, and about 317,000 of the county's 993,000 residents live in the unincorporated balance the county code actually governs. The county's building official may contract with a municipality to enforce the code there, but only where that municipality has itself adopted a code identical in substance, and even then the county will not issue the permit until the municipality has approved the plans against its own zoning. The residential code says the same thing from the other end: a county permit does not relieve anyone from "the zoning ordinance or other applicable laws of any municipality in St. Louis County." Check the municipality, not the county.

SLCRO §§ 1115.050, 1115.051, 1116.050, 1116.051 and § 1116.101 (amended IRC R102.2.2), Ordinance No. 27654, 18 December 2019, read via the Municode API 6 September 2026; municipality count and unincorporated population derived from U.S. Census Bureau Vintage 2024 Subcounty Population Estimates, file sub-est2024_29.csv, SUMLEV 157 records for county FIPS 29189, fetched 6 September 2026

Jennings is on the 2018 code while the county is on 2015

The City of Jennings — an inner-ring municipality inside St. Louis County, 13,024 people on 3.7 square miles — adopted the 2018 International Residential Code as its residential code, along with the 2018 International Building Code, the 2018 International Mechanical Code, the 2018 International Existing Building Code and the 2018 International Energy Conservation Code. The county around it is on the 2015 editions. One county line, two code editions, three years apart, and Jennings takes its authority to adopt from the municipal statutes (RSMo 77.500 and 67.280) rather than from anything the county holds. This is the cleanest proof available that a suburb's answer has to be read from that suburb's own code.

City of Jennings Code of Ordinances ch. 17.1 § 17.1-2 (Ord. No. 2530, §§ 1–2, 27 January 2020), § 7-16 (2018 IBC), § 7-31 (Ord. No. 2534, § 2, 27 January 2020), § 7-18 (Ord. No. 2535, 27 January 2020), § 7-2 (2018 IECC), and ch. 7 state-law reference to RSMo 77.500 and 67.280 — read via the Municode API (productId 11051) 6 September 2026; population and land area from U.S. Census Bureau Vintage 2024 Subcounty Population Estimates and the 2024 Census Gazetteer places file, fetched 6 September 2026

222 farms left, and land in farms fell by half in five years

The 2022 Census of Agriculture found 222 farms in St. Louis County on 21,936 acres, an average holding of 99 acres — the smallest average of any county in the state. Between 2017 and 2022 the number of farms rose 21 percent while land in farms fell 52 percent and average farm size fell 60 percent, which is what subdivision of remaining holdings looks like in the data. 88 of the 222 are between one and nine acres and another 57 are between ten and forty-nine; only twelve are 500 acres or more. Against a 508-square-mile county — roughly 325,000 acres of land — that is what "there is very little left here" means with a number attached.

USDA NASS 2022 Census of Agriculture, County Profile — St. Louis County, Missouri (cp29189.pdf), downloaded and text-extracted 6 September 2026; county land area from the 2024 Census Gazetteer counties file (ALAND_SQMI 507.995), fetched 6 September 2026

Also worth knowing before you build in St. Louis County

Wildwood and the Eureka fringe are the exception: One place in St. Louis County still reads as country. Wildwood holds 35,082 people across 66.681 square miles of land — about 526 people per square mile, against 3,489 per square mile in Jennings — and the Eureka and far-western fringe beyond it is the other pocket where the land question has not already been answered. Both are municipalities with their own councils and their own ordinances, so the county's code and the county's NU zoning are the starting point for the question, not the end of it.
A four-square-mile karst district in north county: St. Louis County zones an approximately four-square-mile area of north county, in the Old Jamestown community, as the KP Karst Preservation District. The ordinance's own account: it is the "Florissant Karst", identified as one of the finest examples of deep funnel-shaped sinkholes in the central United States, internally drained with no surface channels, and presenting "serious constraints to urban development in particular soil creep near sinkhole depressions, localized flooding near sinkholes, and potential groundwater contamination." Development there may not block or fill a sinkhole, route stormwater between sinkholes or discharge developed stormwater into one, and most new development needs a geotechnical report submitted by a geotechnical engineer, with a signed and sealed certification carried on the site plans. A single-family dwelling needs three acres, the same as NU.
The floodplain permit is separate, and it is somebody else's desk: Development in a mapped flood hazard area of unincorporated St. Louis County needs its own floodplain development permit, issued by the Director of Highways and Traffic as floodplain administrator, in addition to the building permit under the Building or Residential Code and a land disturbance permit under the Land Disturbance Code. The county's regulations run against the Flood Insurance Rate Map index panels 29189CIND1A, 29189CIND2A and 29189CIND3A dated 4 February 2015 as amended. A separate permit for each structure is required, and construction may not start on any of them until all are in hand.
The county licenses the trades, not the builder: There is no general or building contractor licence in St. Louis County. Title XI of the county ordinances runs to electrical (ch. 1102), plumbing (ch. 1103) and mechanical (ch. 1108) licensing and contains no chapter licensing general or building contractors at all. The county's own permit machinery shows it: an integrated permit applicant must return the plumbing, electrical and mechanical permit forms carrying the name, signature and licence number of the appropriate subcontractor — the numbers demanded are the trades', not the builder's. Separately, anyone other than the property owner repairing storm damage must register with the building official first.
Metal siding, roof pitch, eaves, design review: the county code regulates none of them on a house: This is the question to settle before a steel package is ordered, because a jurisdiction that forbids exposed metal on a dwelling has made the building unbuildable as drawn. Unincorporated St. Louis County does not. Chapter 1003, the county's zoning ordinance, was read through for exterior material restrictions, minimum roof pitch, minimum eave projection, appearance or design review and minimum dwelling floor area, and the NU Non-Urban and KP Karst Preservation districts — the two that cover what open land the county has left — carry none of them. The word corrugated does not appear anywhere in the chapter. The one materials list in it is a definition, at § 1003.020, of "high quality material" as "building materials that are both durable and attractive including, but not limited to, brick, stone, treated or textured concrete masonry units, and wood", and no district regulation in the chapter invokes it. Two instruments in the chapter can reach appearance, and both are mapped or petitioned rather than general: § 1003.158 Form Based Development is a place-type overlay whose standards run to build-to lines, heights, building types, parking and impervious coverage with no materials palette at all, and § 1003.191 Landmark and Preservation Area is a designation the County Council makes by ordinance parcel by parcel, with "design and construction standards for building facades, setbacks, height, scale, material, color and texture, trim, roof design and landscaping" written into that particular ordinance. The building code says the same thing by omission: the county amends the 2015 IRC chapter by chapter from § 1116.101 through § 1116.144, and the series skips 1116.107 — Chapter 7, Wall Covering, is adopted with no local change, so the model code's own exterior covering provisions are what a plan reviewer here works from. All of that is unincorporated territory, and each of the county's municipalities answers this question for itself.

Below the slab

The expensive surprises are in the ground, not the building

What moves a Missouri budget is usually below grade, and which problem you have depends on where in the state you are. Across the Ozarks it is karst: the Department of Natural Resources maps more than sixteen thousand sinkhole points, and what matters there is what is under the slab rather than what the slab sits in. Across the north and centre it is claypan — dense, slow-draining subsoil that perches water above it for months of the year. In the Bootheel it is deep alluvium carrying the highest seismic demand in the state, where the same soils modelled for liquefaction attack post embedment and slab bearing rather than the frame above them. The same ground then decides the septic system, and Missouri does not run that on a percolation test alone: the rule allows a perc test or a soil morphology examination in a profile pit, and the authority reviewing your parcel picks which. Where a drainfield sits near a sinkhole's drainage, perc testing on its own is not permitted at all. Whether that authority is the state or your own county is itself a local question, and it changes what you have to file. So the site work, the foundation and the drainfield get resolved together rather than one at a time. We price the dirt before we price the building.

What we build in St. Louis County

All nine services are available in St. Louis County. What a build costs depends far more on the parcel than on square footage, so we price against your land rather than publishing a rate card.

Custom Plans

Barndominium floor plans drawn to your parcel and your soil, and to whichever Missouri authority — a county, a city, or none at all — will review them.

Barndominium Kits

Barndominium shell packages delivered to your Missouri land, drawn to the criteria your own county or city publishes — because the state publishes none.

Turnkey Builds

Start to finish barndominium construction in Missouri: the permits that genuinely apply, site work, shell and interior finish, under one contract.

See all nine services

What a build looks like

Three stages every St. Louis County project passes through, from a raw parcel to a finished home. Site work first, because that is where the budget is decided.

Stage one

The parcel

Zoning, setbacks, flood zone and utility access get checked before anything is drawn.

Stage two

Pad and permit

Clearing, grading and a compacted pad, while the submittal works through whichever office issues the permit where you are building.

Stage three

Frame to finish

Shell erected and dried in, then systems, insulation and interior finish through to CO.

Those are the rules where you are building in St. Louis County. Tell us what you want to build and we will draw it to them.

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Where we build around St. Louis County

St. Louis County and the rural land around it. The buildable acreage for a project this size usually sits outside the city limits, which is frequently what changes who issues your permit.

The St. Louis County service area, including the rural acreage outside the built-up edge, which is where the parcels big enough for a build like this usually sit. The map marks the territory we build in. It is not a branch location, and there is no office at this pin.

Keep reading

The questions that usually come next once you know what St. Louis County allows.

Barndominium Cost Guide

Sourced per-square-foot ranges by tier and by size, with a calculator built on the same figures.

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Is It Legal in Missouri?

Classification, zoning, the HOA gate, and why "nonresidential farm building" does not cover a home.

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How Long Does It Take?

Census build-duration data, and what actually sets the permit clock where you are building.

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Nearby areas we build in

Others we cover nearby, and they are not interchangeable. One may be a county with an adopted building code, another a county with no legal authority to have one, another a city that permits inside its own limits whichever county the land sits in. So the office that issues the permit, whether anyone inspects the work at all, the fees, the zoning and the design figures can differ from one card to the next — sometimes across a single property line.

St. Louis

St. Louis (independent city)

Jefferson County

St. Charles County

Franklin County

Building in St. Louis County: common questions

8 questions we get asked most often about building in St. Louis County. If yours is not on the list, ask it directly.

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Is my address in St. Louis County or in the City of St. Louis?

They are two different jurisdictions and neither one contains the other. The City of St. Louis has been an independent city since 1876, meaning it is not part of any county and performs county functions for itself; the Missouri Constitution recognises it "both as a city and as a county" at Article VI, § 31. St. Louis County is a separate charter county that surrounds it. They are peers, not parent and child: different permitting departments, different assessors, different adopted code editions. A mailing address that says "St. Louis, MO" tells you almost nothing about which one you are in — a great many people who say St. Louis mean the county. Check the parcel with the assessor whose jurisdiction you think you are in before you assume.

Can I actually buy land to build a barndominium in St. Louis County?

Very little, and you should know that before you start looking. The 2022 Census of Agriculture recorded 222 farms in the county on 21,936 acres, an average holding of 99 acres, in a county with about 325,000 acres of land — and land in farms dropped 52 percent between 2017 and 2022. What is left is at the western edge, in and around Wildwood and Eureka. If you want acreage inside an hour of the same job and the same schools, the counties to look at are Franklin, Warren, Lincoln and Jefferson, and each of those has a different permitting answer from this county and from each other.

Can I put up a separate shop building next to the house in unincorporated St. Louis County?

Not a large one, and this is the provision that surprises people most. In the NU Non-Urban District — the district that covers the county's remaining open land — detached above-ground accessory structures may cover no more than 7 percent of the lot, each may be up to 400 square feet or 50 percent of the primary structure's footprint whichever is greater, and the ordinance then caps the total: no structure or aggregate of all accessory structures may exceed 1,000 square feet of gross floor area, "regardless of the size of the primary structure or the size of the lot on which it is located." A maximum of two detached accessory structures is allowed, three when one of them is a detached garage, and none may stand in the front yard. That is SLCRO § 1003.107.4.B, as amended 12 February 2026. A shop that size has to be part of the house, not a separate building — or the land has to be somewhere else.

How big does the lot have to be, and how far back does the building have to sit?

In the NU Non-Urban District a single-family dwelling must sit on a tract of not less than three acres, and the same three-acre minimum applies in the KP Karst Preservation District in Old Jamestown. Setbacks in NU are 50 feet from any roadway right-of-way line at the front and 20 feet from every other property line at the sides and rear. Those are the county's numbers for unincorporated territory only — inside any of the county's 88 municipalities the district, the minimum and the setbacks are that municipality's, and several of them are far tighter.

Which building code applies, and what design numbers come with it?

For unincorporated St. Louis County it is the 2015 International Residential Code for One- and Two-Family Dwellings, adopted by Ordinance No. 27654 on 18 December 2019 and codified at SLCRO § 1116.020. The county fills in its own Table R301.2(1) at § 1116.103: 20 lbs/ft² ground snow load, 115 mph ultimate design wind speed (89 mph on the older allowable-stress basis), seismic design category C, severe weathering, a 30-inch frost line depth, slight-to-moderate termite exposure, a 2 °F winter design temperature and a 1,000 air freezing index, with topographic effects, special wind region and wind-borne debris zone all answered NO. The 30-inch frost line is the number that drives a post-frame foundation. Ask any other jurisdiction for its own copy of that one page rather than assuming this one travels.

The county says seismic design category C, but I have seen D for St. Louis. Which is right?

Both, for different purposes, and the honest thing is to say so. The county's adopted table says C, and that is the figure a permit is issued against, because the code derives the category by its own route from the map current when that edition was written and then freezes. Query the USGS Seismic Design Web Service against ASCE 7-16 at Risk Category II and Site Class D for a point in the middle of the county and it returns Ss 0.401 g, S1 0.152 g and category D. Neither source is in error. Use the county's C for the permit, and put both in front of whoever is doing the structural design, because the difference shows up in connection detailing and in the lateral system rather than in the roof.

Does calling the building agricultural get me out of the county's code?

No. Missouri's agricultural exemption lives in the county planning-and-zoning enabling statutes, not in the building-code provisions, and it protects farm buildings "used for such purposes" — the raising of crops, livestock, orchards or forestry. A dwelling is not one of those, and the same statutes list "residence" as a regulated use in their own text. Missouri's property-tax statute draws the same line even more plainly: RSMo 137.017.1 adds the value of buildings customarily associated with farming to agricultural use value "excluding residential dwellings and related land." In St. Louis County specifically, the zoning ordinance names "Dwelling, single-family" and "Farming" as two separate permitted uses in the NU district — they are two different permissions, and the dwelling is the one that carries the three-acre minimum.

Do I need a licensed contractor to build here?

St. Louis County issues no general or building contractor licence — Title XI of the county ordinances licenses electrical, plumbing and mechanical work and contains no chapter for general or building contractors. The county's integrated permit form asks for the name, signature and licence number of the appropriate subcontractor for each of those trades, which is the code's own demonstration of where the requirement sits. Missouri issues no statewide general contractor or residential builder licence either; the Division of Professional Registration's boards include electrical contractors, but no general contractor or home builder board. Two caveats worth knowing: some municipalities inside this county do license or register contractors, and separately, anyone other than the property owner repairing damage after a declared disaster must register with the county building official before starting.

Building in St. Louis County?

Start with the plan. Tell us what you want to build and we will draw it, then confirm which office issues the permit for your parcel, what it will let you put there, and what wind load it has to meet. That conversation costs nothing.

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