Common Barndominium Sizes in Kentucky

Almost every size question about this building type in Kentucky comes in one of two vocabularies. People either ask for a dimension — 30x40, 30x50, 40x60 — or for a living area, usually 1,500, 1,800 or 2,000 square feet. Those are not the same measurement, and the gap between them is where most of the confusion about size, and nearly all of the confusion about cost, actually lives. A 40x60 is 2,400 square feet of footprint; how much of it is heated, floored and finished is a separate decision that can move the answer by half. Underneath the vocabulary there is a Kentucky-specific reason to care about the first number in particular. The Department of Housing, Buildings and Construction wrote its own prescriptive post-frame standard, Section R327 of the 2018 Kentucky Residential Code, and every size limit in it is stated as a width, a height or a spacing — never as a floor area. Table R327.3 then defines what it means by width, in its own column header: building width is the length of the truss, including the overhang. So the first number in 30x40 is the number the code reads, the second one is nearly free, and a page that just lists square footages never gets to any of this.

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What actually changes with this feature

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

48 feet of width, and the eaves count

R327.1's fifth limitation is a maximum building width of 48 feet including the overhang, and Table R327.3 defines building width as the length of the truss including the overhang. That makes the first number in a size the measured one and the second number nearly free — a 40x60 and a 40x100 are the same building on this test. It also means a plan drawn at 48 feet wide with a one-foot eave on each side is already 50 feet by the code's definition and has left the section. None of the three sizes people search for comes close to that line, which is a more useful answer than the vague size warnings the plan catalogues give.

Pier diameter tracks width, not square footage

Table R327.3, Post Frame Pier Diameters, is indexed across the top by building width in feet — 25, 28, 32, 36, 40, 44, 48 — and by nothing else. At a 20 lb roof snow load the diameters run 18, 22, 24, 26, 28, 28 and 30 inches; at 30 lb they run 24, 26, 28, 28, 30, 30 and 32 inches. Footnote 3 rounds a fractional width up to the next column, so a 30-foot-wide building takes the 32-foot row. Stretching a 30x40 to a 30x50 does not touch this table. Widening it to 40 feet does. Note also that the table is indexed to a roof snow load, which is not the ground snow load the county table publishes — a distinction worth keeping straight before anyone sizes concrete off it.

Footprint and conditioned area are different numbers

A 40x60 is 2,400 square feet of footprint. A 40x60 with a 40x30 shop bay is 1,200 square feet of conditioned house inside a 2,400 square foot building, and both get called "a 2,400 square foot barndominium" in ordinary conversation. That single ambiguity is why the search terms split the way they do: somebody typing 30x50 and somebody typing 1,500 square feet may be describing the identical building, or two buildings that differ by a factor of two in everything that costs money to finish. Settle which number you mean before comparing anything to anything.

In six counties the size question is moot

The Kentucky Residential Code's amended Section R301.2.2.2.5 states that prescriptive construction shall not be used for irregular structures located in Seismic Design Categories D0, D1 and D2, and its sixth listed irregularity trigger is when shear walls and braced wall lines do not occur in two perpendicular directions. That is the ordinary barndominium shape — a long open volume with an overhead door consuming one wall line. DHBC's Table R301.2.2.1 puts Ballard, Carlisle, Fulton, Graves, Hickman and McCracken in D2, Calloway, Livingston and Marshall in D1, and Caldwell, Crittenden, Lyon, Trigg and Union in D0. On those parcels the building is engineered by rule at 30x40 just as much as at 40x60, and picking a smaller size does not buy a way around it.

The first number is the one the code reads

In Kentucky the size limit is a width, and the code says which number that is

Section R327 of the 2018 Kentucky Residential Code, Third Edition, is a full prescriptive post-frame standard the Department of Housing, Buildings and Construction wrote itself, and it has no counterpart in the base 2015 International Residential Code the book is built on. Its scope is a list of eight structural limitations, and the size ones are a maximum building width of 48 feet including the overhang, a maximum wall height of 16 feet, a maximum mean roof height of 20 feet and a maximum post spacing of 8 feet. There is no floor-area limit anywhere in it. Table R327.3 removes the ambiguity about which dimension counts by titling its own columns "Building width (length of truss) including overhang" — the truss span, not the ridge run. On that test 30x40, 30x50 and 40x60 all sit inside the width cap with room to spare, and their lengths are irrelevant to it. What actually pushes a building out of R327 is not any of the three popular sizes: it is limitation 1, "residential accessory structures," and limitation 2, "single story." A shop, a barn or a detached garage at these dimensions is inside DHBC's recipe. A building people sleep in is outside it at every size, and R327.1 says what happens next in its own words — structural calculations as required by the residential building official, or design under Section R106.1, or design under the Post Frame Building Design Manual that Section R301.1.1 names as an approved alternative.

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.

30x40

1,200 sq ft footprint · 30 ft truss span · 40 ft long

The smallest of the sizes people ask for, and the one that reads least like an outbuilding from the road once it has a porch on the gable end and real windows in the long wall. Thirty feet of clear span is enough for a great room that does not feel like a corridor and still leaves a full bedroom wing behind it, and 1,200 square feet is a genuine two- or three-bedroom house with no shop in it at all. In Table R327.3 a 30-foot width rounds up to the 32-foot column, so the pier schedule is the same as a 32-foot building's. This is also the size where the sq-ft vocabulary and the dimension vocabulary come apart hardest: nobody searches "1,200 square foot barndominium," but a great many people search 30x40 and mean exactly that.

30x50

1,500 sq ft footprint · 30 ft truss span · 50 ft long

The same 30-foot span stretched by ten feet, and visually that is what it looks like — one continuous ridge, a longer eave line, the same roof pitch reading lower and calmer against the ground. Because the extra area is all length, none of R327's size limits move and Table R327.3's pier diameter does not change; what does change is bracing count, since Section R327.4.6 wants the diagonal bracing on each side of the building at a minimum of 25 feet on centre and within 12 feet of each end. A 50-foot wall takes bracing at both ends and the rule is satisfied. This footprint is also the one that lands precisely on 1,500 square feet, which is why the dimension term and the square-footage term for this size are so often the same buyer.

40x60

2,400 sq ft footprint · 40 ft truss span · 60 ft long

The size the Kentucky search volume concentrates on, and the one that actually looks like the pictures — a 40-foot clear span, a taller ridge, gable-end glass that has somewhere to go, and enough length for a shop bay and a house under one roof line without either feeling squeezed. The most common split is 40x30 of living against 40x30 of shop. Ten extra feet of width over the 30-foot sizes is not a free upgrade: it moves the building from the 32-foot column of Table R327.3 to the 40-foot column, it raises the ridge at any given pitch, and the truss itself is the single component whose weight climbs fastest with span. Length is the cheap direction to grow in this building type. Width is the expensive one, and this is the size where that first becomes obvious.

40x60 with the whole footprint finished

2,400 sq ft, all of it conditioned living space

The same shell with no shop in it. Two thousand four hundred square feet on one level is a comfortable four-bedroom, or a three-bedroom with a study, a proper pantry and a mudroom that is actually big enough to be useful on a farm. It is worth separating this from the shop-and-house version deliberately, because the two are quoted as the same building and finished as very different ones. Everything that costs money per square foot — insulation, air sealing, interior partitions, ceiling finish, flooring, mechanical capacity — doubles between the split version and this one while the shell above it stays identical.

1,800 to 2,000 square feet of living area

e.g. 40x50 finished throughout, or 30x40 over two floors

This is the square-footage vocabulary rather than the dimension vocabulary, and it maps back to footprints in more than one way. Forty by fifty finished throughout gives 2,000 square feet on a single level and keeps every R327 limitation intact. A 30x40 with a second floor gives 2,400 in a 1,200 square foot footprint on far less ground — but it leaves DHBC's prescriptive post-frame section on limitation 2, "single story," and on limitation 4, "no attic storage," before anyone has drawn a wall. Neither of those is a problem; they are simply the point at which the engineering becomes a planned line item rather than a surprise at plan review.

Ways to build this size

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

Pole Barn Kits

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Barndominium Kits

We check barndominium kit packages against the wind, snow, frost and seismic criteria the Kentucky Residential Code publishes for your county.

Custom Barndominium Plans

Barndominium plans drawn to Kentucky's published county design criteria — snow, wind, seismic, frost — with engineering where the code calls for it.

Shop Houses

Shop and living under one roof: how Kentucky's code, zoning and septic rules actually treat a shouse, and where the farm exemption stops.

Common Barndominium Sizes: 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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In a 40x60, which number is the width?

The 40. In post-frame convention the first number is the truss span and the second is the length of the ridge, and the Kentucky Residential Code adopts that convention explicitly rather than leaving it to custom: Table R327.3 titles its own columns "Building width (length of truss) including overhang." That matters because every size limit in Section R327 is written against width, not floor area. The fifth structural limitation in R327.1 is a maximum building width of 48 feet including the overhang, so a 40x60 sits inside it at 40 feet plus eaves, and so does a 30x50 and a 30x40. Their lengths do not enter the test at all. It also means the overhang is not decoration for this purpose — a building drawn 48 feet wide with a one-foot eave each side measures 50 feet by the code's own definition.

Does going from 30 feet wide to 40 feet wide change the foundation?

In a post-frame building, yes, and the code prints the numbers. Table R327.3, Post Frame Pier Diameters, is indexed across the top by building width in feet — 25, 28, 32, 36, 40, 44 and 48 — with a diameter for each at a 20 lb roof snow load and again at 30 lb. At 20 lb the diameters read 18, 22, 24, 26, 28, 28 and 30 inches; at 30 lb they read 24, 26, 28, 28, 30, 30 and 32 inches. Footnote 3 rounds a fractional width up to the next column, so a 30-foot-wide building is designed on the 32-foot row and a 40-foot-wide building on the 40-foot row. Footnote 1 sets pier footing thickness at a minimum of one half the footing diameter. Length does not appear in the table anywhere. That is the clearest statement anywhere in Kentucky code of something builders say informally all the time: growing a building lengthways is cheap and growing it across the span is not.

How deep do the footings go for a post-frame building at these sizes?

Deeper than most people expect, and the requirement does not vary with the size. Section R327.3 states that post and frame structures shall have poured-in-place concrete footings installed below all posts, with the top of the footing a minimum of 48 inches below finished grade and diameters complying with Table R327.3. That is an embedment rule for post-frame construction, not a frost rule, and it sits well below the frost-protection depths Table R403.1.4 assigns — that table carries a 24-inch row covering its "All other KY Counties" default, with 27 inches for Bell, Clay, Knox, Lawrence and Owsley, 30 inches for a list including Boone, Campbell, Kenton, Harlan, Perry and Breathitt, and 33 inches for Floyd, Knott, Letcher, Martin and Pike. So the 48-inch post-frame figure governs the pier depth at 30x40 and at 40x60 alike, and it is a real excavation and concrete quantity that a kit price does not carry.

What does a 40x60 cost per square foot in Kentucky?

We publish no prices, and there is a better answer than a number anyway. The cost figures published on Kentucky-facing barndominium pages run from roughly $25 to $300 a square foot — a twelvefold spread — and none of those pages sources its figure. Three things cause the spread and it is worth being able to grade them yourself. Scope: some figures are a material kit, some a weather-tight shell, some a finished house, and they get printed side by side as though they were the same quantity. Denominator: a 40x60 is 2,400 square feet of footprint, and if 1,200 of that is unconditioned shop then a blended dollars-per-square-foot figure is averaging finished living space with a concrete floor and a bare frame. Almost nobody states the split. Site: land, entrance, driveway, well, septic, power run, grading and rock excavation are excluded from essentially every published number, and eastern Kentucky terrain moves that materially. Ask any quote which of the three it has accounted for, and most of the spread resolves itself.

How many square feet is a 30x40, a 30x50 or a 40x60?

Twelve hundred, 1,500 and 2,400 square feet of footprint. That arithmetic is the easy part; the useful part is that footprint is not the same as living area, and the search terms for these buildings mix the two constantly. A 30x50 is exactly 1,500 square feet, which is why "30x50" and "1,500 sq ft barndominium" so often describe the same house. A 40x60 is 2,400 square feet of footprint but very commonly 1,200 square feet of conditioned house with a 1,200 square foot shop attached, so it is simultaneously a 2,400 square foot building and a 1,200 square foot home. Covered porches and lean-tos add a third number again. Before comparing two plans, two quotes or two published cost figures, check that both are counting the same area.

Is there a size at which I need an engineer?

For a dwelling, the honest answer is that size is not what decides it. The Department of Housing, Buildings and Construction's prescriptive post-frame section, KRC Section R327, opens with eight structural limitations, and the first is "residential accessory structures" and the second is "single story." A shop, a detached garage or a barn at 30x40 or 40x60 sits comfortably inside that recipe. A building people live in falls outside limitation 1 at any dimension, and R327.1 states what follows: structural calculations as required by the residential building official, or design under Section R106.1, or design under the Post Frame Building Design Manual, which Section R301.1.1 lists as an approved alternative to Section R301. Separately, in the counties DHBC's Table R301.2.2.1 assigns to Seismic Design Category D0, D1 or D2, Section R301.2.2.2.5 bars prescriptive construction for irregular structures outright, and one of its listed triggers is shear walls and braced wall lines that do not occur in two perpendicular directions. Plan for the engineering as a line item rather than treating it as a penalty for building large.

Does my county's snow load limit how wide I can build?

It does not cap the width, but it changes what the width costs you underground. Table R327.3 publishes two rows of pier diameters — one for a 20 lb roof snow load and one for 30 lb — and the gap between them is two to six inches of diameter at every building width. That is a roof snow load, which is a different quantity from the ground snow load in DHBC's county table, and conflating the two is a common error. On the ground snow side, Table R301.2(1) prints a value for each of the 120 counties: 20 psf for eighteen of them, including Boone, Kenton, Campbell, Bracken, Mason, Lewis, Greenup, Boyd, Gallatin, Grant, Carroll, Trimble and Henry along the Ohio River and Floyd, Knott, Leslie, Letcher and Martin in the eastern mountains, and 15 psf for the remaining hundred, among them Pulaski, Warren, Fayette, Jefferson, McCracken, Daviess, Hardin, Christian, Laurel and Madison. Wind is the one design figure DHBC does publish for the whole state, and the same table states it plainly: a basic ultimate wind speed of 115 mph for all Kentucky counties, with topographic effects to be investigated — which on a ridge-top site is an instruction rather than a footnote.

If I build it as a farm building, do the size rules still apply?

Only if the parcel genuinely qualifies, and the condition is stricter than most people assume. Both Kentucky code books define FARM as property having a bona fide agricultural or horticultural use as defined by KRS 132.010(9) and (10) which is qualified by and registered with the property valuation administrator in the county where the property sits. KRS 132.010(9) puts general agricultural land at a tract of at least ten contiguous acres, with five acres for commercial horticulture or aquaculture. So the exemption is chained to the county tax roll: a parcel that is not registered agricultural with the PVA is not a farm for code purposes regardless of what is grazing on it, and the exemption also requires the structure to be incident to the operation of the farm and outside the limits of a city. Even where all of that holds, zoning is a separate system and KRS 100.203(4)(c) keeps the dwelling within reach of it. On land that does not clear those tests, none of this changes, and building to the code is what a lender, an appraiser and a valuer will each expect to see anyway.

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The pages that answer the next question this one raises.

Barndominium with a basement

The other way to get more square feet out of the same footprint, and why Kentucky ground makes that a foundation decision first.

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