2-Story Barndominium in Tennessee

The code draws the line, not the marketing. The Tennessee 2018 IRC defines a mezzanine or loft as an intermediate level between the floor and ceiling of a storey with an aggregate floor area of not more than one-third of the room it sits in, and it stays open to that room. The same code says in terms that mezzanines complying with Section R325 "shall not be considered as stories". Cross either limit — cover more than a third of the space below, or close it in — and it is a second storey: its own floor plate, its own structure spanning the building, and a storey that gets counted when a zoning ordinance counts storeys. The one-third figure can go to one-half in a dwelling unit fitted with an automatic sprinkler system, which is a local question rather than a statewide one. If you are looking at a plan and cannot tell which it is, the test is simple: is the upper level open to the room below, and is it under a third of that room's area? If either answer is no, price it as a storey.

Not necessarily, but it is the decision the whole design turns on. A second floor plate over a 40 ft clear span is past every row of the Tennessee 2018 IRC's prescriptive joist tables, which stop at 23 ft 3 in for living areas and 25 ft 7 in for sleeping areas even on their best rows. So it gets solved one of five ways: engineered floor trusses, prefabricated I-joists or structural composite lumber, cold-formed steel floor framing, steel beams that shorten the deck span, or an interior bearing line. The bearing line is the cheapest and it puts structure back in the middle of the ground floor, which is the thing a clear-span building was chosen to avoid. Any of the other four keeps the span open and costs more. We would rather put that choice in front of you with the plan than let it arrive as a change during framing.

Treat that as a no unless the building was engineered for it from the first drawing. A second floor changes the column loads, the connections and the footings underneath them, and none of those are reachable once the slab is poured and the frame is up. Cumberland County puts a number on the footing half of it in its own inspection expectations: 8 inches thick on a single-storey home, 10 inches on a brick or two-storey one. If a second storey is a possibility rather than a plan, the useful move is to have the frame and foundation designed for the future load now and defer only the floor system and the finishes. That costs something up front and it is a fraction of retrofitting.

It depends on the jurisdiction, on the roof pitch, and on where the ordinance measures from — and all three are worth checking before anything is drawn. Unincorporated Hamilton County allows two and a half stories or 35 feet, Robertson County 35 feet with no more than three full or partial stories entirely above grade, Knox County's A zone three storeys and 35 feet, Loudon County three storeys or 36 feet, Wilson County three storeys or 35 feet, Rutherford County and Sumner County 35 feet, and Maury County only two storeys in its RG district. Metro Nashville caps single-family and two-family dwellings at three stories. Williamson County's rural RP-5 and RD-5 districts record maximum height as Not Applicable. The measurement point matters as much as the number: Blount County measures its 35 feet from the highest natural grade immediately adjacent to the structure, so on a cross-slope lot the uphill side is the datum and an exposed lower level on the downhill side does not eat into the allowance. We confirm the cap, the datum and any pitch requirement before the elevation is fixed.

More than people budget for, and it comes out of both levels rather than one. Work it from the code numbers a Tennessee jurisdiction publishes. Knox County's own residential stair handout for the 2018 IRC gives a maximum riser of 7 3/4 inches and a minimum tread of 10 inches. A nine-foot floor-to-floor needs 14 risers at that maximum, so 13 treads at the minimum depth make a run of 10 ft 10 in before you add a landing at either end. At the 36-inch minimum clear width that is roughly 32 sq ft for the flight alone, and closer to 45 or 50 once the landings are in — on each level. Taller ground-floor ceilings, which is normally why someone wants this building type, make the run longer again. Local amendment can change the arithmetic: Loudon County raises the maximum riser to 8 inches and reduces the minimum tread to 9 inches, which pulls the same flight in to 9 ft 9 in, and it shifts the handrail trigger from four or more risers to a total rise of 30 inches or more.

It depends entirely on what you hold constant, and that is the honest answer rather than a hedge. Compared with a single-storey building of the same footprint, adding a second storey is a real added cost: a stair, a floor system that has to span, taller walls, more wall area to insulate and finish, deeper footings and more engineering. Compared with a single-storey building of the same total finished area, the two-storey usually comes out ahead per square foot, because it needs roughly half the foundation and half the roof to deliver the same conditioned space. Both comparisons are legitimate. They answer different questions, and the one you are actually asking decides which number matters.

In practice, yes, and two Tennessee counties say so in their own words rather than leaving you to infer it from R301.1.3. Rutherford County's residential plans review list includes "pole barn type structures with living space regardless of square footage", and its footnote requires that drawings for pole barns or pre-manufactured steel structures intended for occupation "shall be design drawings prepared and sealed by a Tennessee Registered Architect or Engineer", labelled as designed to the edition the county has adopted; the county's published plans review fee is $200.00. Washington County answers its own frequently asked question with "Yes - Anywhere single family dwellings are allowed. Stamped drawings from a design professional are required for all alternative construction methods." Cumberland County requires blueprints by a registered design professional for two-storey homes and for any built-in basement. That is the same conclusion R301.1.3 reaches from the code side: a building whose structural elements exceed the limits of Section R301 is designed in accordance with accepted engineering practice, and a 40-foot clear-span floor plate is well outside those limits. We engage a Tennessee-licensed engineer for the structure and the seal.