Barndominium with a Garage in Missouri

A garage looks like the simplest thing on the drawing and it is the one that most often moves the building. In Missouri the choice between attaching it to the house and standing it off as its own structure changes the setback it has to meet, whether it counts against an accessory-structure cap, and whether a licensed contractor is required to build it. And once living space adjoins a garage or shop bay, two Missouri counties publish a prescriptive separation detail — footing depth, gypsum board, door rating and where a door may not open — that answers "can I live in half of it" better than anything a vendor will tell you.

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What actually changes with this feature

The look is the easy part. These are the decisions that follow from it.

What has to separate the garage from the living space

Greene County Resource Management's Appendix T publishes a section headed "Living Quarters in Barns/Accessory Buildings," and Christian County's Building Regulations Department publishes the same specification. The dividing wall between the living side and the garage or shop side needs a minimum of half-inch gypsum board applied on the garage side, continued to the underside of the roof; the area over the living space must be insulated and its ceiling carries half-inch gypsum board; windows are not allowed between the living area and the garage at all; and a door from the garage into the living area must be solid wood not less than 1⅜ inches thick, solid or honeycomb steel of the same thickness, or 20-minute fire rated — Greene County adding that "Panel doors do not have the required rating or thickness." No door or window may open into a sleeping area from the garage side.

The footing under it, which is not the house's footing

Greene County's Appendix T sets its own foundation rule for living quarters in an accessory building: footings must extend to the exterior wall side of the supporting post on a pole-type structure, with the bottom of the footing a minimum of 18 inches below finish grade, footings a minimum of 12 inches wide and 8 inches thick with two rows of #4 rebar supported at least 4 inches off the bottom, lapped and tied. Christian County publishes the same 18-inch minimum, 12-by-8-inch footing and two rows of #4 rebar. Note that 18 inches against the City of Springfield's published 24-inch frost line in the same county — one county, two depths, decided by which side of the city line the parcel sits on. Across the jurisdictions that publish their own Table R301.2(1), the sourced spread is wider still: 36 inches in Kansas City and Lee's Summit, 30 in Columbia, Boone County, St. Charles County and St. Louis County and City, 24 in Springfield, 18 in Branson, Nixa and the city of Ozark, and 15 in Sikeston.

How much garage the lot is allowed to carry

Two Missouri cities meter garage space against lot area rather than against the house. Columbia's Unified Development Code provides that for a one-family lot one garage space is permitted per 2,000 square feet of lot area and that total garage space shall not exceed the total habitable first-floor area of the primary dwelling. Lee's Summit limits a detached garage outside the AG district to 250 square feet for each 5,000 square feet of lot area, with a maximum of 2,500 square feet for lots under five acres and 3,500 square feet at five acres or more, and permits only one garage structure — while its AG row reads simply "No limitation on size in AG." Branson takes the third route and caps all accessory structures in a residential district at 800 square feet combined, unless a special use permit is granted.

The floor drain, which cannot go where people assume

Missouri's minimum construction standards for on-site sewage disposal systems, 19 CSR 20-3.060(4)(A), require all liquid waste and washwater to discharge into the sewage tank and then except a specific list: "Roof, garage, footing, surface water, drainage, cooling water discharges and hazardous wastes shall be excluded from the sewage tank." A garage floor drain, a wash bay and roof and footing drainage therefore need a designed route that is not the septic system. On a slab-on-grade metal or post-frame building that is a decision made before the pour, alongside the vapour retarder and any sub-slab radon provision — Columbia, for instance, adopts the residential code's radon control appendix and amends it to apply "without regard to zone designation," so the national radon map does not settle it there.

The attached/detached decision

In Missouri, detaching the garage is a code decision before it is a design one

The Platte County Zoning Order of 1990 is the sharpest sourced illustration in the state. Section 400.130(D) gives a dwelling in the AG district a 30-foot side yard on an interior lot and a 100-foot front yard — and then requires "accessory buildings other than dwellings" to sit not less than 100 feet from every exterior and interior side lot line, with the rear yard 100 feet for the dwelling and 50 feet for an unattached accessory building. On a narrow tract, detaching the garage can cost seventy feet of side yard that attaching it does not. The count matters too: St. Louis County's SLCRO § 1003.107.4.B allows a maximum of two detached accessory structures in the NU Non-Urban District, "three when one of them is a detached garage," while capping all of them together at 1,000 square feet of gross floor area regardless of lot or house size. And two cities tie garage space directly to the land underneath it — Columbia allows one garage space per 2,000 square feet of lot area and provides that total garage space shall not exceed the total habitable first-floor area of the primary dwelling, while Lee's Summit's Table 6.IV-1 limits a detached garage outside the AG district to 250 square feet for each 5,000 square feet of lot area, capped at 2,500 square feet under five acres and 3,500 at five acres or more, with only one garage structure permitted. None of that is a preference. It is four jurisdictions writing four different consequences onto the same decision.

Common ways to build this

Common configurations we see. Yours does not have to match one exactly — this is a starting point for the conversation, not a catalog.

Attached garage on the house's slab

2 bays attached / 1,800 sq ft living

The configuration that generally avoids the accessory-structure caps and the detached-accessory setbacks, at the cost of bringing the separation detail above into play at the shared wall. In Platte County's AG district this is the difference between a 30-foot side yard for the dwelling and a 100-foot side yard for a detached accessory building. Confirm with the reviewing office in writing that an attached garage is reviewed as part of the principal building on your parcel rather than as an accessory structure, because the ordinances quoted here are written for detached buildings.

Detached garage as a third structure

900 sq ft garage / separate 2,000 sq ft house

Where the garage stands alone it counts against whatever accessory rule the jurisdiction runs. In St. Louis County's NU district a detached garage is the reason a third detached accessory structure is allowed at all, and all of them together still stop at 1,000 square feet. In Lee's Summit outside AG only one garage structure is permitted and its size is metered at 250 square feet per 5,000 square feet of lot. Jackson County requires detached accessory buildings to sit in the rear yard, with a detached garage the single exception to that rule.

Garage bays inside the barn envelope

3 bays / 1,600 sq ft living, one structure

The shop-house arrangement, where the garage doors and the living space share one frame. This is where Greene County's and Christian County's published separation specification does the most work: insulated and covered walls floor to ceiling around the living area, half-inch gypsum on the garage side of the dividing wall continued to the underside of the roof, no windows between the two, a rated or solid 1⅜-inch door, and no door or window opening into a sleeping area from the garage side.

Ways to build this size

A footprint can go together several ways. These are the service lines most relevant to it.

Post-Frame Homes

Post-frame and pole barn construction built as a dwelling — with a straight answer on Missouri's farm-building exemption, a zoning exemption only.

Metal Homes

Metal-clad homes built to the standard your own jurisdiction sets — and specified in writing, because across much of Missouri no county inspector will ever see the envelope.

Permitting & Approvals

Establishing who actually has authority over your parcel, then carrying the approvals that genuinely apply — which in much of Missouri is not a building permit.

Barndominium with a Garage: common questions

8 questions we get asked most often about this footprint. If yours is not on the list, ask it directly.

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Is an attached garage or a detached garage easier to permit in Missouri?

It depends entirely on the jurisdiction, and the difference can be large enough to redesign the site plan around. The Platte County Zoning Order § 400.130(D) sets a 30-foot side yard for the dwelling in the AG district and not less than 100 feet for accessory buildings other than dwellings, so attaching is worth 70 feet of side yard there. St. Louis County allows two detached accessory structures in the NU district and three when one is a detached garage, but caps them at 1,000 square feet combined. Lee's Summit permits only one detached garage structure outside AG and meters its size against lot area. Jackson County requires detached accessory buildings to be in the rear yard and expressly exempts a detached garage from that rule. What is consistent is that the accessory-structure rules in every one of those ordinances are written for detached buildings — so the practical question to put in writing is whether your reviewing office treats an attached garage as part of the principal building, and what setback it then has to meet.

What has to go between the garage and the living space?

Greene County and Christian County both publish the answer, and it is the same answer. The wall between the living area and the garage or barn needs a minimum of half-inch gypsum board applied on the garage side, continued to the underside of the roof; every wall around the living area must be insulated and covered floor to ceiling; the area over the living space must be insulated with half-inch gypsum board on the ceiling; windows are not allowed between the living area and the garage at all; a door from the garage into the living area must be solid wood not less than 1⅜ inches thick, solid or honeycomb steel of the same thickness, or 20-minute fire rated, and Greene County notes that "Panel doors do not have the required rating or thickness"; and no door or window may open into a sleeping area from the garage side. This is the identical specification described on the shop page of this site, because the counties' documents do not distinguish between a garage bay and a shop bay. Outside Greene and Christian counties there is no reason to assume the same figures apply — Missouri has no statewide residential building code, and whatever code edition your own jurisdiction adopted governs instead.

Can I put living space over the garage?

Sometimes, and it is worth asking two separate questions. On zoning, unincorporated Jackson County's rule for an accessory dwelling unit expressly contemplates it: an ADU may be built only in the AG and RR districts, on a building permit, and "is limited to one storey unless it sits over a garage," with a ceiling of 1,000 square feet of heated area, and the county's permit packet applies the same 1,000 square foot ceiling to finished area inside a garage or pole barn. Christian County's Zoning Regulations cap the living area in an accessory structure at 1,000 square feet, and Boone County caps a permitted accessory dwelling at 75 percent of the primary dwelling's floor area or 1,500 square feet, whichever is less. On construction, note the limit of what Greene County and Christian County actually publish: their specification addresses the wall between the two halves and the ceiling over the living area. A habitable room sitting above a garage is a different geometry from a living area beside one, and it should be put to the building official in writing rather than inferred from those documents. The loft page on this site covers what a room above changes structurally.

Can the garage be bigger than the house?

In some Missouri jurisdictions the ordinance answers this directly and the answer is no. Columbia provides that total garage space shall not exceed the total habitable first-floor area of the primary dwelling, and separately that the aggregate first floor square footage of all accessory structures shall not exceed the first floor square footage of any principal structure. Springfield allows one Secondary Building at no more than half the principal building's footprint, and § 36-5.03.B.6 provides that anything beyond the limits "shall be treated as a second principal building and meet all lot and building design standards for a principal building." Boone County and Columbia both define an accessory structure as one that "shall not exceed the height of the main structure," so a taller garage fails even where a larger one might pass. At the other end, Lee's Summit's AG row prints "No limitation on size in AG" and St. Charles County's "A" district states no maximum square footage at ten acres or more.

Do I need a licensed contractor to build a detached garage?

In two of the sourced Missouri jurisdictions, yes, at thresholds a real garage clears easily. Kansas City Code § 18-14(j) requires anyone contracting to construct, structurally alter or enlarge a one- or two-family dwelling "including detached accessory buildings in excess of 400 square feet in area" to be licensed as a residential building contractor or to work under one, and § 18-16(b)(1)a exempts from a building permit only a one-storey detached accessory building whose projected roof area does not exceed 200 square feet. Lee's Summit requires a permit for a detached accessory structure over 120 square feet, sealed drawings above 600 square feet, and a contractor holding at least a Class C city licence for a building over 600 square feet or more than one storey — unless the owner is building it themselves, in which case no contractor certification is required. Springfield's exemption is narrower still, covering only "One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided the floor area does not exceed 100 square feet," with the same section stating that "Work not listed herein shall be assumed to require a permit unless indicated otherwise in writing by the building official." Missouri has no statewide general contractor licence, so this is a purely local question and the answer changes at the city line.

How deep does the garage slab and footing have to go?

Whatever your own jurisdiction publishes, and the sourced spread across Missouri is more than twofold. Kansas City Code § 18-57 and Lee's Summit Code § 7-902 both publish a 36-inch frost line depth; Columbia, Boone County, St. Charles County, St. Louis County and the City of St. Louis publish 30 inches; Springfield publishes 24; Branson, Nixa and the city of Ozark publish 18; Sikeston publishes 15. Greene County's Appendix T sets a separate 18-inch minimum below finish grade specifically for the footings under living quarters in a pole-type accessory building, and Christian County publishes the same. On a post-frame garage that number sets the depth of every post hole, so it is the figure that moves the excavation quote before it moves anything else. There is no statewide Missouri frost depth to fall back on; ask for the jurisdiction's own Table R301.2(1) in writing.

Can the garage go in front of the house?

Frequently not, and the rule is usually about position rather than size. Jackson County's UDC § 24005.2(c)(1) requires detached accessory buildings to be placed in the rear yard and prohibits them in front of the principal building, with a detached garage the only exception to that rule. Lee's Summit's Table 6.IV-1 prohibits front placement for a detached garage in AG. St. Louis County's NU district allows no detached accessory structure in the front yard. Columbia requires detached accessory structures to sit behind the principal structure. Springfield requires a Secondary Building to be set behind the front of the principal structure, three feet from side and rear lines and at least ten feet from the principal building, and adds a design requirement — the accessory building "shall be compatible with the principal building considering materials, architectural details and style, window and door details, and roof forms."

Will my garage doors and steel siding be allowed?

Check the zoning ordinance for an exterior materials clause, because at least one Missouri metro county writes one. Clay County's Land Development Code § 151-10.6 excludes smooth, ribbed or corrugated metal or plastic panels as house siding and corrugated, galvanized and zinc roofs, and sets a 4:12 minimum pitch and a 12-inch eave — a stock steel package does not clear that. Lee's Summit does not ban materials but does require at UDO § 8.030.C that accessory buildings comply with the design standards required for the principal building and that "The exterior building materials and colors shall be similar to the principal building," with § 6.1350.F.4 applying the same test to any detached garage or storage building over 120 square feet. Boone County, Camden County and Taney County were each checked and carry no exterior material restriction, no minimum roof pitch and no design review for a site-built dwelling. Where a rule does exist, it is often buried in a manufactured-home subsection and does not reach a site-built house at all, which is why the clause has to be read rather than summarised.

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