30' x 40' · 1,200 sq ft footprint

30x40 Barndominium Floor Plans in Illinois

A 30x40 is the entry size for barndominium floor plans, and it is more flexible than 1,200 square feet sounds. Thirty feet is a comfortable clear span for a post-frame or steel frame, so there is no interior bearing wall deciding where the rooms go: the partitions are placed for the plan, not for the structure. Built as a house, a 30x40 carries two bedrooms comfortably and three with a tight hall. Built as a shop-house, it gives a one-door bay and a compact one-bedroom living end. The decisions that shape a 30x40 are the split between living and shop, the sidewall height you need for a door, and whether it will be permitted as the home or as a second building on the lot. In Illinois that last question is answered by your county or municipality, and the answers differ a lot between neighbouring counties.

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What actually changes at this size

The dimensions are the easy part. These are the decisions that follow from them.

A 30-foot clear span leaves the plan open

Trusses spanning the full 30 feet put the loads on the sidewall posts or steel columns, so interior walls are partitions you can place anywhere. That is what makes a 30x40 work as either a two-bedroom house with an open great room along one gable end, or a shop-house with a demising wall on a frame line. Roof trusses are designed to the snow load your county publishes rather than one figure for the whole state: Peoria County lists a 20 pound ground snow load for unincorporated homes, while McHenry and Kane counties list 30.

Two bedrooms comfortably, three if the hall is tight

At 1,200 square feet of living, a 30x40 fits two bedrooms, two baths, a laundry and an open kitchen and living room with room to spare. A third bedroom is possible with a short central hall and one shared bath, and it is the layout people most often ask for as a starter home or a retirement downsize. Once a shop bay takes part of the footprint, plan on one bedroom, or two small ones at the 720-square-foot living split.

Sidewall height is set by the door you want

A 10-foot sidewall suits a house and a standard garage door. A 12- to 14-foot wall allows a taller overhead door for a pickup with a rack or a small tractor. Before you pick the taller wall on a second building, check your county's accessory height cap: Madison County's is 20 feet in residential districts and 25 feet in agricultural ones, and Champaign County's is 15 or 24 feet depending on whether the lot is under or over an acre. Measured to the mid-point or the peak, a steep roof on a 14-foot wall can reach those numbers quickly.

Footings go below the frost line your county publishes

Posts, piers and slab edges have to sit below the local frost depth. McHenry, Kane, Will, DeKalb, Winnebago, Rock Island and Peoria counties each publish 42 inches for unincorporated areas; Tazewell County's garage handout gives 36 inches. Rock Island County has also proposed, in the 2021-code amendments it scheduled for 1 October 2026, that residential wood columns not be encased or embedded in concrete, which would move a post-frame 30x40 there onto piers or brackets.

House or second building

The same 30x40 is judged differently as the home than as a building beside one

As the principal dwelling, a 30x40 goes through your building department's new-home process, which in some counties is strict from the start: Will County's building ordinance requires every new one- or two-family residence to have documents signed and sealed by a registered design professional, or as approved by its chief building official. Built as a second building on a lot that already has a house, the 30x40 is an accessory structure, and accessory rules are about height and size rather than bedrooms. Madison County's zoning booklet caps accessory buildings at 25 feet in its agricultural and conservation districts and 20 feet in residential districts, and Champaign County allows 15 feet on lots under an acre and 24 feet on lots of an acre or more. Tazewell County's garage handout says that if the structure will include habitable space, you stop and apply for a new dwelling instead. Decide which of the two you are building before the drawings start, because the answer changes the permit, the plans and sometimes the wall height.

How people actually split 1,200 sq ft

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

Two-bedroom house

1,200 sq ft living

The whole footprint as a home: two bedrooms and two baths at one gable end, a laundry and mudroom by the entry, and an open kitchen and living room under the rest of the span. A covered porch along one 40-foot sidewall adds outdoor room without adding to the conditioned floor area. This is the simplest 30x40 barndominium plan to permit, because it is plainly a house.

Living end with a working bay

480 sq ft shop / 720 sq ft living

A 30x16 shop with one overhead door and a 30x24 living end holding a one-bedroom plan, or two small bedrooms with a shared bath. The shop and the living space share a wall, so a fire-separation detail and a tight door between them belong on the drawings. This split works best as a first building on acreage where a larger house may follow.

Three-bedroom starter

1,200 sq ft living, three bedrooms

Three bedrooms along one sidewall off a short hall, one full bath plus a half bath, and a combined kitchen and living room across the other side. Closets and the laundry are tucked against the hall to keep circulation space small. It is a working family plan on a small footprint, and a covered porch or a detached garage is the usual next addition.

Ways to build this size

A 30' x 40' footprint can go together several ways. These are the service lines most relevant to it.

Custom Plans

Custom and modified barndominium plans drawn for your Illinois lot, your county's code and the kit or build we quote — sealed where your county requires.

Pole Barn Homes (Post-Frame)

Pole barn homes built post-frame for Illinois acreage: wide clear spans, fewer footings, and posts and footings set to your county's rules.

Shouses

Shouse and shop house builds in Illinois: a heated shop and a finished home under one roof, planned around your doors, your county and your land.

Barndominium Kits

Barndominium kits for Illinois land: shell kits or fuller packages, sized to your county's snow load and frost line, delivered and put up by our crew.

30x40 Barndominium: common questions

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

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Is a 30x40 big enough to live in?

Yes. At 1,200 square feet a 30x40 barndominium holds a comfortable two-bedroom, two-bath plan, and a three-bedroom plan with one full bath and a half bath. The open span helps: with no bearing walls inside, you are not losing space to structure. Where it gets tight is when part of the footprint becomes shop, because every foot of shop comes out of the living end. Settle the split first and the rest of the plan follows.

Can I build a 30x40 now and live in it while I build the main house?

Only if your county or municipality allows both parts: living in an accessory building and occupying the site before the main house is finished. The rules differ by county, so ask the building and zoning office before you commit. Tazewell County's garage handout, for example, says that a structure with habitable space goes through the new-dwelling process rather than the garage permit. In Kendall County's agricultural zoning, the county's general rule is one home for each 40 acres, so a second dwelling on a smaller ag parcel may not be available at all.

Do I need a permit for a 30x40 barndominium?

Where your city, village or county has adopted a building code, yes. Illinois does not issue residential building permits itself; the local government does. Madison County, for example, requires a permit for any accessory structure over 200 square feet, far below a 30x40. Some counties issue only a zoning or filing permit: Williamson County's permit application is filed with the Supervisor of Assessments, and its ordinance names no building code. Where no local code applies, the Illinois Residential Building Code Act (815 ILCS 670) requires the construction contract for a new home to name the code it will be built to.

Do 30x40 barndominium plans need a sealed set?

It depends on the county. Illinois's Architecture Practice Act does not require an architect for a detached single-family residence on a single lot, unless a local ordinance does (225 ILCS 305/3). Some counties do require a seal: Will County requires signed and sealed documents for every new one- or two-family residence, and Kane County requires a sealed pier design for detached accessory buildings that sit on piers instead of a turned-down slab. Where a seal is required, a licensed Illinois structural engineer seals the drawings for your project.

Is a 30x40 cheaper per square foot than a larger barndominium?

Usually not. The site costs are nearly the same whatever the size: driveway, pad, power, well and septic. Septic design is based on a soil investigation with at least three borings (77 Ill. Adm. Code 905.55), and that work costs the same for a small house as a large one. What a 30x40 saves is shell, slab and finish, which is real money but a smaller share of the total than people expect. Build a 30x40 because it is the size you want, not to lower the cost per foot.

What changes if my 30x40 is on farmland?

Less than people hope. A barndominium someone lives in is a dwelling, not an agricultural building, in almost every county. Tazewell and Williamson counties' building rules exclude farm residences on operating farms, but the energy code, the plumbing code and the septic permit still apply there. McHenry, DeKalb and Will counties exempt agricultural structures, not houses, and Rock Island County's agricultural building definition says it shall not be a place of human habitation. If you are not farming the land, plan on building to the county's residential code.

Want this drawn for your program and your parcel? That is where a build actually starts.

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Start your plans

Tell us what you want to build and we will draw a 30' x 40' building for your program, then confirm what it looks like on your parcel, who issues the permit, and a realistic budget range. That conversation costs nothing.

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