In covering the tornadoes that struck Moore, Okla. May 20, the topic of safe rooms and storm shelters comes up a lot because most wall and roof systems cannot stand up to a direct hit of an F5 tornado.
Or can they? Some of our readers have some concrete ideas.
Structural concrete panels
In the comments section of an earlier post, Richard Sims, of Sims Construction asks about standard building practices:
"It is not a choice to build earthquake-safe in Calif. It is not a choice to build Hurricane-safe in Fla. Its time to wake up and build safe in tornado and fire zones as well. Why only build a room and not a SCIP safe room? What about houses made with Insulated Concrete Forms?"
Looking at Sims' website, it is clear that Mr. Sims builds with Structural Concrete Insulated Panels (SCIPs), which seems like a great choice with many benefits.
Architect Robert Bissett from Idaho decided to use our forum to write a letter to the Governor of Oklahoma, Mary Fallin. Mr Bissett joined the 'Bricks-not-sticks' chorus pitching the merits of monolithic concrete structures with domes and Structural Concrete Insulated Panels (SCIPs). He says that SCIP homes are a little more expensive, but that the benefits far outweigh the cost and risks.
Other concrete ideas
After the Greensburg, Kansas tornado of 2009, we wrote about Silo Homes -- circular concrete structures that mimic a grain silo, which helps it to be ultra tornado-resistant. It is easier for wind to bend around a circle than a square. Silo Home was a demonstration home with all of the green building bells and whistles thrown in -- like the atmospheric water generators (which take humidity out of the air and convert it into drinking water) and the PV arrays (installed when PV cost twice what it does today).
Perhaps these bells and whistles kept Silo Home's design from being adopted during the Great Recession.
What seems good about Silo House: air-tightness, insulation levels, and impact resistance.
What seems impractical about Silo House: It is much more expensive than the local market can bear -- even without the bells and whistles.
I had an email exchange recently with Alex Lukachko of Building Science Corporation, who was an architect with the company when the tornados hit Greensburg, he had a surprising story to tell about cost and impact resistance:
We can build structures to survive exposure to those kind of winds but they won't look like normal houses and they won't be built like normal houses. They also won't cost anything close to what a normal house costs.
In Greensburg, we were proposing energy-efficient new construction with a relatively low cost - something like $120K per house. But many of the houses in the area were only worth a faction of that. I seem to remember that the average sale price of a house in the area was something like $75K . . . and you could buy a lot with an old house on it for as little as $5K.
What this means is that the resources are just not there to pay for average-sized American homes and at the same time protect them against flying trees, 2x4s, etc.
We had this same problem rebuildingto higher standards after Katrina.
This is a hard pill to swallow when your community has been destroyed and your are trying to rebuild your life.
An article from Sep 2012 looked at a precast concrete home that can withstand 200 mph winds.
ForeverHome is a total precast concrete home that is engineered to withstand hurricane-force winds. The foundation and floor system are cast on site, while the interior and exterior walls and roof are done in the factory. Everything is then assembled on site.
The precast roof surrounds a continuous layer of insulation. The roof and wall patterns are cast into the surface of the concrete. A waterproof membrane is bonded to the surface of the roof to prevent water leaks.
Aerated autoclaved concrete (AAC):
Jeff Ramsdell commented on The Tornado Shelter Debate that stick-framed houses are bad for tornado zones and that it is time to lean forward with our thinking.
"As long as we build stick-frame envelopes--the debris fields will look like pick-up sticks, and the injuries will rival IEDs. It is time to think long and hard about alternative build materials.
Perhaps the folks, especially public officials, in Tornado Alley should investigate autoclaved aerated concrete, or AAC
Jeff closes his comment by encouraging people to buy AAC from him by posting his email and website. The editors are not against small businesses drumming up business wherever they can, and we actually like AAC as a product. Furthermore, we are impressed by Mr. Ramsdell's passion for his product. He reminds us of us. And, we wish that he would not sell his products in our comments section.
Unlike concrete masonry units, AAC blocks are solid, with no molded core holes. Standard blocks are 8 inches high, 24 inches long, and 4 to 12 inches thick. An 8x8x24-inch block weighs only 35 pounds, so it's easier to handle than a conventional concrete block. AAC can easily be tooled also, and even cut, drilled, and shaped with woodworking tools.
Four inches of AAC has a 4-hour fire rating, making it ideal in commercial buildings for encasing steel columns, surrounding elevator shafts, and for other fire-stopping requirements.
Engineered Reinforced Concrete
Eugenio Aburto takes the pick-up-sticks bait from Ramsdell:
I think the above assumption is not true. There is a material: REINFORCED CONCRETE, and a technology; STRUCTURAL ENGINEERING, which can design dwellings capable of resisting nature.
Just set the parameters of the stress and let the professionals go to work, he says.
He then jumps into the 'Buy My Product' thread saying that he has built residential and commercial buildings in earthquake and hurricane zones of Mexico using a proprietary construction method (he even lists the patent number).
Myself after building thousands of houses in Mexico City (earthquakes), houses and hotel in Cancun (hurricanes) refined CRCM (Concrete Rib Construction Method patent US 8,429,876 b2).
Underground homes, anyone?
Coming soon: ICF and wood-frame construction resources
Photo credit: Samir Valeja (This image is from the FEMA Photo Library.) [Public domain], via Wikimedia Commons