ROCK SOLID: Homes built to withstand severe weather

(SOURCE: WMC Action News 5)
(SOURCE: WMC Action News 5)

MEMPHIS, TN (WMC) - With terms like hold-downssheer walls and wind-loads, today's building codes are written to give Mid-South homes a fighting chance against the forces of nature.

Allen Medlock, Shelby County's chief building official and a 52-year veteran of building codes, explained all homes in Arkansas, Tennessee and Mississippi fall under the 2012 International Residential Code. He said the code requires homes to be built to minimum seismic and wind-load specifications.

"Which in this area are 90 miles per hour," Medlock said. "As far as seismic, the Mid-South must withstand specifications for Category D." According to the U.S. Geological Survey (USGS), Category D would fall under a "severe" rating -- an 8 out of 10 - on the Modified Mercalli Intensity Scale. The scale defines severe as "...damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse...damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned."

"Most houses are built a lot better than they used to be, simply because of the seismic and wind-loads that have to be met," said Medlock. "In the past when you built a house, you just nailed a bottom plate down and stand the wall up and then fasten it down. Now, they're tied together from that footing through the structure, basically (with) sheer walls in them (and) specific hold-downs at each end of a sheer wall. Most of the sheer walls are anywhere from four feet to eight feet, and with proper hold-downs tied into the footings and properly fastened, they should meet the seismic codes."

"The intent is (to withstand) wind or hurricane," said Collierville, Tennessee, home-builder Dave Moore. Moore gave us a tour of a home he's building in Piperton, Tennessee. He showed us how the steel hold-downs bore deep into the home's concrete foundation. Then steel plates and straps are installed in the walls, along the framing, all the way up on the roof rafters. Moore said the construction works together to create a steel curtain against the minimum 90-mile-an-hour wind-load.

In case you're wondering, that's an EF-1 tornado.

"Generally, what happens is it knocks the windows out as it's coming around," Moore said. "The wind goes into the building, and it has to go somewhere, so it pushes up, and that's generally when the roof comes off. What we're trying to do with the straps from the foundation to the plates, the plates to the studs, the studs all the way up is to hold it down."

"It just ties the whole structure together. Makes it more seismic resistant, too," added Medlock.

Another construction method to steel homes against earthquakes and severe weather is insulated concrete forms, or ICF. The walls of an ICF-constructed house have four inches of a foam-like material. The foam surrounds a solid six-inch core of rebar and concrete, making the walls almost a foot thick.

"This six-inch core will actually resist 250 mile-an-hour winds (EF-4 tornado)," said Robert Young, ICF builder for ICF Building & Supply of Searcy, Arkansas. "Engineered right, an eight-inch wall will resist 300 mile-an-hour winds (EF-5 tornado)."

Brian Sprouse is building his new home in Mason, Tennessee, with ICF after a tornado touched down barely a mile from his former home three years ago. He said not only is ICF tight against tornadoes, but it is also energy-efficient. He said when his house is complete, it will be 5,200 square feet, but his power bill will be between $70-100 thanks to smaller heating and air conditioning units and to the nearly one-foot thick ICF walls. "These walls are going to cost about $10,000 extra, (but) we'll recoup all of that in seven years just through the energy efficiency," Sprouse said.

"It should be pretty well seismic-resistant, also," said Medlock of ICF construction. He said the residential code does not specifically cover ICF, except that a state-licensed structural engineer must design, plan and pull permits for the construction.

Medlock said there's another thing the code doesn't cover that it should cover: mandatory storm shelters or safe rooms in the Mid-South's highest risk areas for tornadoes. "I think they should be put in mobile home parks, that sort of thing," he said. "You might not save a trailer, but you'd save a life, and I believe that eventually (mandatory storm shelters) will happen."

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