Barndominium with a Wrap-Around Porch in Tennessee

Yes, and it is the detail most often missed. IRC R401.3 requires impervious surfaces within ten feet of the building foundation to be sloped not less than two percent away from the building, and it requires the grade to fall not fewer than six inches within that first ten feet. A porch deep enough to put furniture on is eight to twelve feet deep, so it occupies that entire zone and its own slab or deck is the impervious surface the clause is describing. Two percent is about a quarter of an inch per foot, which is roughly two and a half inches of drop across a ten-foot porch. On a covered floor people expect to be level, two and a half inches is visible. It changes the column base heights, the step at every door onto the porch, and where the water leaves. Beyond the porch edge the six inches of fall still has to be achieved, or a drain or swale constructed under the section's own exception, which on a flat parcel with a deep wrap is often the real answer.

It is inside the engineering, not outside it. The residential code lets a house be built prescriptively to one of a short list of standards, named at R301.1.1: the AWC Wood Frame Construction Manual, AISI S230 for cold-formed steel framing, or ICC 400 for log structures. A clear-span rigid frame or a post-frame building is none of the three, so R301.1.3 governs, and it says structural elements exceeding the limits of Section R301 or otherwise not conforming to the code shall be designed in accordance with accepted engineering practice. Those section numbers hold across every edition in use in this state. Two counties have reached the same conclusion in their own documents: Rutherford County's residential plans-review list names pole barn type structures with living space regardless of square footage and requires drawings sealed by a Tennessee registered architect or engineer, and Washington County answers in its own guidance that stamped drawings from a design professional are required for all alternative construction methods.

Because it is an order of magnitude past the point where an overhang stops being an overhang. Published framing guidance limits ladder framing to overhangs of roughly eight to twelve inches and switches to outrigger framing above twelve inches. A usable porch roof projects eight to twelve feet. On top of that, the deck provisions of the residential code state that deck ledgers shall not support concentrated loads from beams or girders, and a covered porch's roof beam is precisely that kind of load. So the beam cannot be picked up by a ledger bolted to the band joist. It lands on a column, the column lands on its own footing, and every joint between roof member, beam, column and footing is a designed connection. Technical guidance from the Building America Solution Center puts metal connectors at three of those locations for exactly this reason, and describes an attached porch as needing a strong and continuous load path from the roof to the foundation.

Below the frost line, and the depth is a jurisdiction figure rather than a state one, because Table R301.2 is filled in locally. Eight of the jurisdictions we work in publish theirs. Twelve inches is the figure in Knox County and the City of Knoxville, Loudon County, Jefferson City, Alcoa, Maryville, Clarksville, Montgomery County and Cumberland County. Maury County publishes ten inches. Cumberland County's own document states it in the terms this page cares about: deck footings must extend below the frost line, which is twelve inches below the virgin earth. Those are shallow depths, and that is genuinely good news for a porch. But depth is not size. A porch post carries a concentrated point load down onto ground that in this state can be rock at one column and deep residual soil at the next, so each footing is sized for its load, its span and what it is actually bearing on. Confirm the criteria for your own parcel rather than borrowing a neighbouring county's.

Rarely as an appearance question, often as a dimensional one. Most of the jurisdictions we work in set no minimum roof pitch, no required overhang, no required porch and no exterior material standard on a detached single-family dwelling at all. What does bite is measurement. Washington County allows uncovered porches, steps, terraces and ramps to project ten feet into the required rear yard, and the word doing the work is uncovered, so a roofed wrap gets no projection and has to sit inside the full setback. The City of Murfreesboro replaced IRC R302.1 with a local rule that keeps exterior walls and their projections, including decks and roof overhangs, at least five feet from a side lot line. And because a covered porch is roofed, it counts toward lot coverage everywhere and toward impervious area where that is measured, which is where Sevier County's fifteen percent Critical Slope Overlay cap and Maury County's ten percent AP district cap start to matter. In Nashville, Metro's stormwater capacity fee runs on total post-construction impervious area and is payable in full before grading permit approval, so the porch has a line on that bill.

Screening one bay is usually the right call and screening the whole wrap usually is not. Where you put it can be a rule rather than a preference. Robertson County defines a porch as a roofed open area that cannot be heated or air conditioned, and states that side and rear porches may be screened but front porches may not be screened or enclosed in any manner, so on a Robertson County wrap the screened bay goes on a side or rear leg. Screening does not make it living space, and heating it can cost you more than you expect: in Robertson County a heated or air-conditioned area stops meeting the county's own definition of a porch, and conditioned space is what the Adequate Facilities Tax is measured on at $1.50 per square foot, while the porch itself sits outside that base. Sumner County draws the same line on its adequate facilities tax form, which excludes garages and open porches while including an unfinished basement or bonus room. Practically, a screened bay stays at ambient humidity all summer in climate zones 3A and 4A, and its bottom rail forms a continuous low element close to grade, so it gets detailed with the same care as the base of a wall.