Callaway County No code adopted here

Barndominium Builders in Callaway County, MO

Callaway County is the land bank north of the Missouri River from Jefferson City, and it answers the building-code question in a way almost nobody publishes. It is one of only three second-classification counties in Missouri on the Missouri Association of Counties list published May 2025, which means RSMo 64.170 empowers it to adopt a building code — and it has not. The County Commission publishes a signed letter, reissued every year and current for 2026, that says in eleven words what a land buyer most wants to know: Callaway County has not adopted planning or zoning, and no occupancy permits or building permits are required in unincorporated areas. That is not the same as saying nothing is inspected. The letter names three offices instead of a building department, and between them they are the real gate. The Callaway County Sewer District — organised by countywide vote in August 2018 and now the contact point for on-site septic permitting — administers a county sewage ordinance under which no new construction may be occupied until the sewer system has passed a final inspection, and under which the sewer permit form is the document that produces your 911 address. The county's floodplain administrator answers for anything in a mapped flood hazard area. Road and Bridge issues the right-of-way access permit without which no driveway entrance may be built onto a county road. Inside the cities the answer changes again and it changes twice: Fulton permits and inspects under the 2015 International Residential Code adopted by Ordinance No. 1439-17, and Holts Summit under the 2012 International Residential Code adopted by Ordinance No. 2654 — two editions, twelve miles apart, in one county, and neither of them fills in Table R301.2(1) with a local wind speed, snow load or frost depth. The ground is the other half of the story. The Missouri River is a soil boundary as well as a county line: Callaway carries about 83,074 acres of claypan soils where Cole County, across the water, carries none, and just over half the county's map units are rated somewhat poorly drained or worse. On that ground the foundation conversation starts with water that sits on top of a dense subsoil for months, not with rock.

Callaway County at a glance

County: Callaway County
Population: 45,126
ZIP codes: 65251, 65043, 65231, 65063, 65262, 65059, 65067, 65077, 65080, 63388
Site visits: Same-week site visits across Callaway County — Fulton, Holts Summit, New Bloomfield, Auxvasse, Kingdom City, Millersburg, Williamsburg, Mokane, Tebbetts, Steedman and Portland, and the section roads between them. The line that matters here is not a county line but a city limit: 25,736 of the county's 45,126 residents live outside every incorporated place, and that is where the ground rules change completely.

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Building conditions in Callaway 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 Callaway 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 may have a building code and has chosen not to

Callaway is second classification, one of only three counties in that class statewide. RSMo 64.170(1) empowers 'the county commission in all counties of the first and second classification' to control construction and issue building permits, and RSMo 64.205 repeats that sections 64.170 to 64.200 'shall apply to all counties of the first and second class'. So the power exists here — which is the opposite of the position in the 89 third-classification counties, where the legislature has never granted it and no commission vote could create it. Callaway has not exercised it. Any future adoption would run through RSMo 64.170(2), which requires voter approval from a county that had no code before 28 August 2001, and RSMo 64.170(3), which limits the vote to the affected unincorporated area. Classification is set by assessed valuation rather than population under RSMo 48.020, and it moves.

RSMo 64.170 (effective 28 Aug 2008), RSMo 64.205 (effective 28 Aug 1963) and RSMo 48.020 (effective 28 Aug 2026), rendered from revisor.mo.gov and read 8 Sep 2026; Missouri Association of Counties, 'Missouri Counties by Classification', published May 2025, mocounties.com/s/Missouri-Counties-by-Classification-2025.pdf, downloaded and text-extracted 8 Sep 2026 — CLASS 2 (TOTAL 3): Callaway, Lincoln, Newton

The county says so itself, in a signed letter it reissues every year

The Callaway County Commission publishes a planning-and-zoning letter, signed and posted as a separate document for 2022, 2023, 2024, 2025 and 2026, and prints the same text on the county website with the note that the information 'is current as of 2022, 2023, 2024, 2025, and 2026 … it has not changed'. The operative sentences are 'Callaway County has not adopted planning or zoning' and 'No occupancy permits or building permits are required in unincorporated areas of Callaway County'. The letter then names the only three contacts for new construction — the sewage ordinance, the floodplain ordinance, and the county road and bridge engineer — and lists the incorporated places that may have their own rules: Fulton, Holts Summit, Lake Mykee, New Bloomfield, Mokane, Kingdom City and Auxvasse. That is a rare thing to find published at all, and it is why the county limit matters less here than the city limit.

Callaway County, Missouri, 'Callaway County Planning and Zoning Information', callawaycounty.org/commission/callaway-county-planning-and-zoning-information/, read 8 Sep 2026, with the signed 2026 letter posted at /wp-content/uploads/2026/03/Planning-and-Zoning-Information-2026.pdf; corroborated by the county's 'Ordinances, Policies, and Resolutions' index, callawaycounty.org/commission/ordinances-and-policies/, read 8 Sep 2026, which lists 30 instruments and no building code and no zoning ordinance

Septic is the permit, and it is what gets you an address

The Missouri Department of Health and Senior Services records Callaway's on-site wastewater authority type as Ordinance, with the Callaway County Sewer District as the contact — so the county applies its own standards rather than the state minimum, and the three-acre exclusion in RSMo 701.031 for single-family lots does not appear in the county's version of that section at all. What the county ordinance does say is unusually direct. Every on-site single-home system needs a permit to install or upgrade, and contractors must notify the office at least 24 hours before work. An engineering design stamped by a Missouri-certified professional engineer is required for any new construction on a lot under two acres, and for any site whose soil morphology shows poor suitability. Anyone applying for an official address must first register with the district on the sewer permit form, which the district then forwards to the county Emergency Operations Center for the address to be issued. And no new construction may be occupied until final inspection of the sewer system. There is also no grandfathering of existing systems in this county.

Missouri Department of Health and Senior Services, OWTS Construction Permit Process county selector, health.mo.gov/business-professionals/onsite-wastewater-treatment/owts-construction-permit-process?county=Callaway, read 8 Sep 2026 — Agency: Callaway County Commission; Authority Type: Ordinance; Callaway County Sewer Ordinance §§ 701.031, 701.043 and 701.046, effective 1 March 2006 and revised 15 November 2011, as posted by the Callaway County Sewer District at callawaysewer.org (both the 'Revised sewer ordinance 2025' and 'Revised Sewer ordinance – Sewer District Authority' copies), read 8 Sep 2026; Callaway County Sewer District, 'On-site Single Home', 'About Us' and 'FAQs' pages, read 8 Sep 2026

The Missouri River is where the claypan starts

Callaway County's soil survey covers 542,355 acres, and about 83,074 of them — 15.3 percent — carry a Central Claypan series as a major map-unit component: Mexico on 64,565, Armstrong on 13,635, Putnam on 4,760 and Leonard on 114. Cole County, immediately across the Missouri River, carries none of those series as a major component at all. The USDA's own description of the Mexico series puts the top of the claypan 7 to 18 inches down, calls the soil poorly drained with very slow permeability, and records a perched water table with an upper limit of half a foot to a foot and a half below the surface from December to May in most years. The county's single most extensive soil is not even a claypan series: Keswick, on about 86,545 acres, is a smectitic, somewhat poorly drained soil with a perched saturated zone at about a foot from April to June and a linear extensibility of more than 6 centimetres in the top metre — which is the shrink-swell criterion in its own taxonomic class. Overall, 272,677 acres of the county, just over half, are rated somewhat poorly drained, poorly drained or very poorly drained.

USDA-NRCS Soil Data Access (SDMDataAccess.sc.egov.usda.gov/Tabular/post.rest), queried 8 Sep 2026 for survey areas MO027 (Callaway) and MO051 (Cole), joining legend → mapunit → component on majcompflag = 'Yes'; USDA-NRCS Official Series Descriptions for MEXICO and KESWICK, soilseries.sc.egov.usda.gov/OSD_Docs/M/MEXICO.html and /K/KESWICK.html, rendered and read 8 Sep 2026; drainage-class acreages from the muaggatt table for MO027, same query session

Two cities, two code editions, and neither one fills in the design table

Fulton adopts the 2015 International Residential Code for One and Two Family Dwellings at City Code § 18-156, by Ordinance No. 1439-17 of 8 August 2017, alongside the 2015 IBC, IEBC, IPMC, IMC, IPC, IFC and IFGC and the 2017 National Electrical Code. Holts Summit adopts the 2012 International Residential Code at § 10-1, by Ordinance No. 2654 of 11 May 2017 effective 1 June 2017, alongside eleven other 2012-edition ICC codes. Neither city adopts an International Energy Conservation Code at all, which matters more for a metal-skinned building than for a stick-built one, because the envelope specification is most of the job. And neither publishes a filled-in Table R301.2(1): Fulton's amendment section says only 'Table R301.2(1) AS SPECIFIED IN THE ADOPTED CODE', and Holts Summit's adopting section makes no Table R301.2(1) amendment. The nearest thing to a published local figure in either code is Fulton's insert of 24 inches at IRC § P2603.5.1 and IPC § 305.4.1 — the minimum depth for a building sewer below finished grade, not a footing frost line. Fulton also limits the residential sprinkler requirement to structures of three or more storeys, and Holts Summit states that internal sprinklers are not required in any new residential structure.

Fulton, Missouri, Code of Ordinances ch. 18 arts. II–X, §§ 18-31, 18-45, 18-56, 18-81, 18-106, 18-131, 18-133, 18-156, 18-158, 18-166 and 18-176 (Ord. No. 1439-17, 8-8-17; as amended by Ord. Nos. 1468-18, 1477-18 and 1516-19), Municode Supplement 33, online content updated 27 March 2026, codified through Ordinance No. 1703-25 enacted 18 November 2025, read 8 Sep 2026 and § 18-158 re-read after independent re-navigation the same day; Holts Summit, Missouri, Code of Ordinances § 10-1 (Ord. No. 2654, §§ 2—5, 5-11-2017), Municode Supplement 14, online content updated 28 July 2026, codified through Ordinance No. 2891 enacted 9 December 2025, read 8 Sep 2026

Inside Fulton, the shop may not outgrow the house

Fulton's zoning chapter caps detached accessory buildings on a ten-band ladder keyed to lot size — 500 square feet up to 7,000 square feet of lot, then 780, 950, 1,080, 1,500 at half an acre to an acre, 2,000, 2,500, 3,000, 4,000 at two and a half to five acres, and at five acres or more '5,000 square feet for each 5 acres of property owned'. Combined accessory structures may not cover more than 30 percent of a rear yard, no single one may exceed the table, and there must be ten feet between them. Two general rules bite harder than the table. An accessory structure 'shall be subordinate in area, extent of use, and fair market value to its principal building or structure', and 'accessory buildings may not be used for dwelling purposes'. A shop larger or more valuable than the house does not clear that inside the city limits. The ladder is written for the R-1, R-2, R-3, C-1, C-2 and MH-1 districts and does not name the A-1 agricultural district, where Fulton sets no minimum lot area, no minimum frontage, a 45-foot height limit and allows two or more principal buildings on a lot. None of it reaches the unincorporated county, which has no zoning at all.

Fulton, Missouri, Code of Ordinances §§ 120-31(f) and 120-111 including Table 4, Graduated Increase in Accessory Structure Size (Ord. No. 1583-22, § 1(Att.), 4-26-22), Municode Supplement 33, codified through Ordinance No. 1703-25 enacted 18 November 2025, read 8 Sep 2026 and re-read after independent re-navigation to § 120-111 the same day

Also worth knowing before you build in Callaway County

Exterior materials, roof pitch and floor area: what the codes here actually say: Fulton's zoning chapter contains no restriction on exterior wall or roof materials, no minimum roof pitch for a dwelling, no minimum eave projection, no architectural or design review of a single-family house, and no minimum dwelling floor area — its R-1 district table sets a 7,000-square-foot lot, 65 feet of frontage, 25-10-25 setbacks, a 35-foot height limit and one principal building per lot, and nothing about appearance. The only roof-pitch figure in the chapter is a 3:12 threshold in the solar-array access provisions, and the only mention of architectural character is in the supplemental data required for a planned unit development site plan. Holts Summit is different in kind rather than in degree: § 48-401, 'Exterior appearances', requires that 'the exterior appearance of all buildings shall be in reasonable conformance with the exterior appearance of other structures in the immediate vicinity' — a compatibility test that names no material, no pitch and no eave, but that does reach every building in every district. Auxvasse's zoning does carry a 3:12 minimum pitch and a materials list, but only inside its definition of a 'prefabricated home', and that definition expressly includes steel siding as an acceptable exterior. None of these reaches unincorporated ground.
Fire districts here are fire districts, not building departments: RSMo 321.220(12) lets a fire protection district board adopt ordinances whose standards may be 'industrial codes adopted by nationally organized and recognized trade bodies', which in some Missouri counties has made a district the only construction authority on the ground. It has not happened here. Holts Summit Fire Protection District, North Callaway Fire Protection District and South Callaway Fire Protection District each publish a full public site and none of them names an adopted building, residential or fire code, a permit programme or a plan review; two of the three state plainly that they have no burning regulations either. Two things are worth knowing alongside that. RSMo 321.228, effective 28 August 2012, provides that where a city or county adopts, implements and enforces a residential construction regulatory system, fire districts inside it are 'without power, authority, or privilege' to run one — so inside Fulton and Holts Summit, which both do, a district could not take that role even if it wanted to. And RSMo 321.220(12) itself bars a district from imposing regulations or requiring permits 'with respect to the erection, maintenance, repair, alteration, or extension of farm buildings or farm structures', which is a carve-out for farm buildings and not for a dwelling.
The Callaway Energy Center does not reach your house: The county's nuclear station sits at the centre of a 10-mile plume exposure pathway emergency planning zone and a 50-mile ingestion exposure pathway zone, as the State Emergency Management Agency defines them. Both are emergency-preparedness constructs: they create planning, notification and public-information duties for government and the operator, and they produce sirens, alert-radio arrangements and the county's Smart911 notification system for residents. They are not a land-use instrument. Nothing in the county's complete published index of ordinances, policies and resolutions, nothing in the Commission's signed planning-and-zoning letter, and nothing in the Fulton or Holts Summit building or zoning chapters attaches any siting rule, setback, design requirement, disclosure duty or permit to a parcel's position inside either zone. Stated plainly because it is the kind of thing a buyer worries about and nobody answers: for the purpose of building a house on land in Callaway County, the plant changes nothing about what you may build or what approvals you need.
A stormwater permit exists on the Holts Summit side and nowhere else in the county: Because the unincorporated ground around Holts Summit and Jefferson City is dense enough to fall inside the Census-defined Jefferson City Urban Area, that part of Callaway County is a regulated municipal separate storm sewer system and holds a state operating permit. The county adopted MS4 Stormwater Regulations on 15 October 2024 under RSMo 64.907 — a statute that authorises any county subject to the federal stormwater rules to regulate, with no reference to county classification at all. Inside the mapped area a land disturbance permit is required before disturbing more than one acre, and separately before grading more than 3,000 square feet or using motorised equipment in or near a sinkhole, losing stream, cave, spring, wetland or other sensitive feature, with a stated minimum initial fee of $300. The same regulations set a construction restriction that reads like zoning and is not: no house, building or other structure may be built within 60 feet of the ordinary high-water mark of a watercourse or other drainage facility, or with openings below one foot above the 1% annual chance flood elevation. Projects exclusively agricultural or silvicultural are exempt, and individual lots in a new subdivision are treated as part of the subdivision rather than as separate projects.
You need a permit for the driveway even though you need none for the house: Callaway County maintains 820 miles of road, and its Policies and Specifications for Road Construction and Acceptance require a Right of Way Access Permit from the Road and Bridge Department before constructing any driveway entrance, temporary or permanent, onto a county-maintained road. The location must be approved before construction. The department sets the pipe diameter and final location; the minimum culvert is 15 inches in diameter and 24 feet long, a culvert longer than 30 feet steps up one pipe size, nothing longer than 50 feet goes in without prior approval, and all driveway culverts must be annular riveted corrugated metal pipe with at least Aluminized Type 2 coating or HDPE — 'no galvanized pipes will be allowed'. The owner buys the pipe; the county installs it and covers it with one load of rock. Where the entrance is onto a state route instead, the Missouri Department of Transportation requires its own permit to work on its right of way for construction of a driveway or modification of an existing one, and Callaway sits in MoDOT's Central District. A city entrance is a third answer again.
New Bloomfield is not in the flood insurance programme: Callaway County itself joined the National Flood Insurance Program's regular phase on 3 January 1985 and remains a participating community, as do Fulton (15 June 1983), Mokane (18 September 1986), Kingdom City (8 March 2006) and Holts Summit (16 January 2007); the effective flood insurance rate map for all of them dates from 5 September 2012. The City of New Bloomfield does not participate in the NFIP — a status FEMA has recorded, with the sanction that accompanies it, since 2 May 1976. That is a live commercial fact rather than a technicality: flood insurance written through the federal programme is not available in a non-participating community, which is a problem for any lender that requires it on a parcel inside a mapped special flood hazard area there. On the county side of the line the floodplain administrator is the county's emergency management director, and the county carries a Floodplain Management Ordinance and flood damage prevention resolutions in its published index.
Karst is not the story here — bedrock and bottomland are: The Missouri Department of Natural Resources sinkhole inventory holds 16,001 records statewide. Seven of them fall inside Callaway County. Cole County across the river has nine; Boone County, one county west, has 438. So the sinkhole checks and setbacks that dominate a build in the karst counties are largely beside the point on this ground. Two other measurements matter more. About 92,689 acres of the county — 17.1 percent — sit in map units whose shallowest bedrock is 20 inches or less, concentrated in the dolomite bluff country along the Missouri River and the Auxvasse and Loutre drainages, where Gasconade soils and mapped rock outcrop together account for roughly 37,000 acres. And about 133,955 acres, a quarter of the county, sit in map units with a seasonal high water table within 30 inches of the surface. Those are two different foundation problems on two different parts of the same county, and which one a parcel has is a question the soil survey answers before anyone digs.
Most people here already live where there is no code: The Census Bureau's 2024 population estimates put Callaway County at 45,126, of whom 12,573 are in Fulton, 4,714 in Holts Summit, 1,023 in Auxvasse, 744 in New Bloomfield, 187 in Mokane, 135 in Kingdom City and 14 in the sliver of Jefferson City that crosses the river. That leaves 25,736 people — 57 percent of the county — in the balance of the county, outside every city limit. The agricultural census counts 1,271 farms on 289,024 acres, an average of 227 acres, made up of 142,478 acres of cropland, 65,801 of pasture and 62,830 of woodland; 525 of those farms are between 50 and 179 acres and 308 are between 10 and 49. Land in farms fell 12 percent between 2017 and 2022. This is not a county where acreage has to be hunted for at the edges — it is most of what the county is.
Auxvasse codifies buildings without adopting a building code: Not every incorporated place in this county runs a building department, and the difference is worth checking before assuming a city limit means inspections. Auxvasse has a full chapter headed Buildings and Building Regulations, and what is in it is a lead-pipe ban, a demolition permit procedure, a dangerous-buildings article with a building inspector and building commissioner, and a building-numbering article — with no adopted building code, no adopted residential code, and no building permit requirement anywhere in the chapter. Its zoning sets a 6,000-square-foot minimum lot in R-1 with 65 feet of width, limits accessory buildings to 30 percent of a rear yard without capping their floor area, and sets no minimum dwelling floor area. Its whole zoning chapter was re-adopted by Ordinance No. 773-2025 on 17 December 2025.
This county is close to changing classification, and it would not change the answer: RSMo 48.020 sets the first classification at an assessed valuation of $900 million and over, the second at $600 million and up to that figure, and directs in subsection 2 that the required valuation for each classification be increased annually by the change in the CPI-U, with the State Tax Commission calculating and publishing the indexed amount. The Commission's 2024 annual report gives Callaway County a total assessed valuation of $1,104,624,464 — $1,066,745,651 locally assessed plus $37,878,813 in centrally assessed companies. Under RSMo 48.030.3 a county may move to the first classification once its valuation qualifies and its governing body elects to change. A reader watching that should know what it would and would not do. It would not create or remove building-code authority, because RSMo 64.170 reaches the first and second classifications alike, and it would not lift the referendum requirement in subsection 2. It is a reason to date any statement about this county's class rather than treat it as permanent.

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 Callaway County

All nine services are available in Callaway 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.

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What a build looks like

Three stages every Callaway 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 Callaway County. Tell us what you want to build and we will draw it to them.

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Where we build around Callaway County

Callaway 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 Callaway 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 Callaway 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.

Boone County

Jefferson City

Cole County

Columbia

Boone County

Building in Callaway County: common questions

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

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Do I need a building permit to build a house in unincorporated Callaway County?

No. The County Commission's own signed letter, reissued for 2026, states that no occupancy permits or building permits are required in unincorporated areas of Callaway County, and that the county has not adopted planning or zoning. What that settles is that the county does not permit or inspect the building. It does not settle that nothing is required of you. Before the house is occupied the Callaway County Sewer District has to have permitted the on-site wastewater system and passed a final inspection on it; if any part of the site is in a mapped flood hazard area the county's floodplain administrator has to be satisfied; if the driveway meets a county road you need a right-of-way access permit from Road and Bridge, and if it meets a state route you need one from the Missouri Department of Transportation; and if the parcel is in the unincorporated urbanised area near Holts Summit and you disturb more than an acre, you need a land disturbance permit under the county's MS4 stormwater regulations. Inside Fulton, Holts Summit, Auxvasse, New Bloomfield, Mokane, Kingdom City or Lake Mykee the answer changes entirely and you should ask the city.

Could Callaway County adopt a building code later, after I have built?

It could, and this is one of the counties where the question is real rather than academic. Callaway is second classification, and RSMo 64.170(1) empowers county commissions in the first and second classifications to control construction and issue building permits — so unlike the 89 third-classification counties, the power exists here and is simply unused. Two limits sit on any future adoption. RSMo 64.170(2) provides that a county which had not adopted a building code before 28 August 2001 has no authority to adopt one unless the voters approve it, and nothing the county publishes records any earlier code. RSMo 64.170(3) then limits that vote to the area affected, meaning voters in incorporated territory do not decide it. And under RSMo 64.180 a county code reaches unincorporated territory only. A code adopted in the future would not reach back and make an already-built house unlawful, but it would govern later additions and alterations, which is one good reason to keep your build documentation.

There is no county code. Does that mean nothing about my build is inspected?

No, and the distinction matters. What the county's classification and its own letter establish is that the county does not inspect the building. Several other things about the same project are inspected by someone. The septic system is permitted and inspected by the Callaway County Sewer District under a county ordinance, and the district's rule is that at least 80 percent of systems constructed, modified or repaired are inspected, with no backfilling before approval and no occupancy of new construction before the final sewer inspection. Anything in a flood hazard area answers to the county floodplain administrator. A driveway entrance is inspected by whichever road authority owns the road. Electrical service is a matter between you and your utility. And a lender or insurer will very often want an engineered foundation design regardless of whether any government asks for one — which, on claypan ground, is a reasonable thing for them to want.

The claypan keeps coming up. What does it actually mean for a foundation?

A claypan is a dense clay layer close to the surface that water cannot get through quickly. The USDA description of the Mexico series, which covers about 64,565 acres of this county, puts the top of that layer 7 to 18 inches down, calls the soil poorly drained with very slow permeability, and records a perched water table sitting between about six inches and a foot and a half below the surface from December through May in most years. So for roughly half the year the top of the profile can be saturated while the layer below it stays effectively sealed. Practically that means three things. Surface and roof water has to be taken away from the building deliberately rather than allowed to pond. The clays involved are smectitic, which is the shrink-swell mineralogy, so footing depth and slab detailing are decisions to make on measured soil data rather than on habit. And a septic drainfield in very slow soil is a design problem, which is why the county requires an engineering design stamped by a Missouri-certified professional engineer on lots under two acres and wherever soil morphology shows poor suitability. Order a soil investigation on the actual building footprint before the slab is designed.

How big a shop can I build next to the house?

In unincorporated Callaway County there is no zoning at all, so there is no accessory-building size cap, no coverage limit and no rule that the shop be smaller than the house. The practical limits are your septic design, your driveway and culvert, your setback from any watercourse if you are in the MS4 area near Holts Summit, and your own budget. Inside Fulton the answer is very different. Fulton caps detached accessory structures on a ladder by lot size, from 500 square feet on the smallest lots up to 5,000 square feet for each five acres owned at five acres and above, limits all accessory structures together to 30 percent of a rear yard, requires that an accessory structure be subordinate in area, extent of use and fair market value to the principal building, and prohibits accessory buildings from being used for dwelling purposes. That combination is what a shop-first buyer needs to read before choosing a lot inside the city. Holts Summit sets no accessory floor-area cap but does require every building's exterior appearance to be in reasonable conformance with structures in the immediate vicinity, and its agricultural district has a five-acre minimum lot.

Is metal siding or a metal roof restricted anywhere in this county?

Not on a site-built house in unincorporated Callaway County, where there is no zoning ordinance to restrict anything, and not in Fulton, whose zoning chapter carries no exterior material restriction, no minimum roof pitch for a dwelling, no eave requirement, no design review of a single-family house and no minimum dwelling floor area. Two things elsewhere in the county are worth knowing precisely rather than vaguely. Auxvasse's zoning sets a 3:12 minimum roof pitch and lists acceptable exterior materials, but only inside its definition of a prefabricated home — and that definition expressly names steel siding as one of the acceptable materials found on standard houses. Holts Summit has no material list and no pitch rule, but § 48-401 does require that the exterior appearance of all buildings be in reasonable conformance with the exterior appearance of other structures in the immediate vicinity, which is a judgement standard rather than a specification. If you are buying inside Holts Summit and planning an all-metal exterior, that is the section to raise with the city before you close.

What does the nuclear plant mean for building a house here?

For the build itself, nothing. The Callaway Energy Center sits inside a 10-mile plume exposure pathway emergency planning zone and a 50-mile ingestion exposure pathway zone as the State Emergency Management Agency defines them, and those zones create planning, notification and public-information duties for government and the plant operator. For a household they produce emergency preparedness — sirens, alert radio, the county's Smart911 notification system and periodic public information — and not a construction requirement. The county's published index of ordinances, policies and resolutions contains no instrument tied to the zone, the Commission's planning-and-zoning letter names only the sewage, floodplain and road contacts for new construction, and the Fulton and Holts Summit building and zoning chapters attach no siting rule, setback, material requirement or permit to a parcel's position inside it. There is no additional approval to obtain and no design change to make because a parcel is inside the ten-mile ring. It is worth registering for the county's alert system, which is a sensible thing to do anywhere in the county.

Is there a minimum acreage before I can put in a septic system?

Callaway is an ordinance county, so the state's general three-acre exclusion for single-family lots in RSMo 701.031 is not the operative rule here — the county's own version of that section omits the exclusion entirely and requires that all new construction pass a final sewer inspection before the building is occupied. The county sets no minimum lot size for an on-site system. What it sets instead is a design threshold: on a lot smaller than two acres, or on any site whose soil morphology examination shows poor suitability, the system has to be an engineered design carrying the stamp and number of a Missouri-certified professional engineer. A soil morphology report is the starting point, and the district publishes a list of soil scientists working in the county. A homeowner may not install the system personally unless they hold a state installer number. And there is no grandfathering of existing systems in this county, so if you are buying a parcel with an old system on it, get it evaluated by a state-licensed inspector before closing rather than after.

Where in the county is land actually available, and how much of it is there?

Most of the county. The 2022 agricultural census counts 1,271 farms on 289,024 acres in Callaway, averaging 227 acres, and 833 of those farms are under 180 acres, which is the size range most barndominium buyers are shopping in. The Census Bureau's 2024 estimates put 25,736 people — 57 percent of the county — outside every city limit. The practical geography splits three ways. The south and west, around Holts Summit, New Bloomfield and Millersburg, is the commuter side, closest to Jefferson City and Columbia and the only part of the county touched by the MS4 stormwater regulations. The centre, around Fulton, Millersburg and Hatton, is the deepest claypan and the flattest ground. The north and east, around Auxvasse, Williamsburg and Kingdom City, is farm country on I-70 with the longest drive times. And the river frontage along the south edge, from Mokane through Tebbetts to Portland and Steedman, is bluff and bottomland, where bedrock is shallow in places and floodplain mapping matters most.

Building in Callaway 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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