Deck building
in Smithville

Yes. Smithville's development department lists decks, covered decks and covered porches among the projects that need a building permit, and the city's residential deck guidelines open with the statement that a permit is required for the construction of a residential deck. The guidelines don't set aside a class of low or small decks the way some cities' codes do, and the city's building guidelines state that Smithville requires permits and inspections for all construction.

The city's "When Do I Need a Permit?" flyer defines the scope broadly. A permit is required to construct, enlarge, alter, repair, move or demolish a structure, and the work that doesn't need one is ordinary minor non-structural repair, such as painting and similar finish work. Cleaning and staining a deck falls on the no-permit side. Rebuilding the frame, or tearing out a deck and building a new one, falls on the permit side.

Three administrative rules come from the same flyer. A homeowner who owns or occupies the house may be issued a permit to do the work themselves. Every contractor performing work in Smithville must hold an occupational license with the city, and the building guidelines add that a general contractor can hold a blanket occupation license covering its subcontractors. If work begins before the permit is issued, the regular permit fee is doubled.

The site plan is an overhead drawing, and the application lists what it has to show:

• the deck's footprint in relation to the existing house
• the location of any stairs being added
• the location of the columns, with horizontal measurements
• the distances from both side property lines and the rear property line
• which side of the house is the front yard and which is the rear

By signing, the applicant certifies that the deck is designed in accordance with the City of Smithville's Deck Guidelines. That certification is what ties the drawing to the structural charts below, since the post sizes, pier diameters and joist spans on the plan are the ones the guidelines allow.

The application also carries a state notice: disposal of demolition waste is regulated by the Missouri Department of Natural Resources under Chapter 260 RSMo, and that waste goes to a demolition landfill or a sanitary landfill. It applies whenever an old deck comes down before a new one is built.

Smithville's deck guidelines are written to the 2018 International Residential Code and size every deck for a load of 40 pounds per square foot, then turn that load into charts a deck plan is drawn from:

Footings

piers extend 36 inches below grade and bear on undisturbed soil. Their diameter comes from Chart B, which pairs each pier size with the deck area it can support, from an 8-inch pier for 14 square feet up to a 24-inch pier for 126 square feet.

Post connections

mechanical post bases are required to connect the posts to the piers.

Posts

Chart A sets the maximum post height by species, post size and the deck area each post carries.

Joists

spans come from the IRC tables. A No. 2 pressure-treated 2x8, for example, spans 12'-10" at 16 inches on center and 11 feet at 24 inches.

Ledger

Chart E sets the size and spacing of corrosion-resistant lag screws for each range of joist span.

The charts work together. A longer joist span puts more load on the ledger, so Chart E calls for lag screws spaced more closely, and it puts more deck area on each post and pier, so the post and pier charts call for larger sizes.

Smithville's zoning code allows decks into required yards, within a limit. Under Sec. 400.310(C), open porches, covered porches, elevated decks, covered elevated decks, patios and covered patios may extend into any required yard by no more than 30 percent of that yard's required dimension. Every 10 feet of required yard allows 3 feet of encroachment.

That's why the application asks for measured distances to both side lines and the rear line. For a deck builder in Smithville, a deck's depth, a stair that turns toward a side yard and the post locations near a lot line are all checked against the 30 percent limit. The deck guidelines add one step that comes before any of it: locate the easements and the exact property lines first, since a recorded easement can rule out ground that zoning would otherwise allow.

Most of Smithville's homes are recent. The median Smithville housing unit was built in 1996, according to Census Bureau American Community Survey estimates for 2020 to 2024. About 68 percent were built in 1990 or later, and about 12 percent before 1960.

The current code is newer than most of those houses. Smithville adopted the 2018 IRC in Sec. 500.030 of its municipal code, effective November 2, 2020, and its local climate table sets the frost line at 36 inches, rates weathering as Severe and puts the air freezing index at 1,034. A deck built with a home from the 1990s or 2000s was permitted under an earlier code and earlier versions of the city's charts. When that deck is replaced, the new one is drawn and inspected under the 2018 code, with piers sized from Chart B, mechanical post bases and a ledger fastened to the Chart E pattern.

For a deck builder in Smithville, the house's age also says something about its deck. On a 1990s or 2000s home, the deck standing today is often the original, and the question is whether its frame can stay or the structure has reached the point of replacement.