 |
|
Form definitely follows function in this storm shelter. Its real beauty is in its ability to protect the homeowners from violent weather.
|
By Chuck Ross
They can masquerade as closets, wine cellars and even bathrooms, but safe rooms are unique constructions. Homeowners may not be able to see many of the structural differences between these spaces and the rest of their residences, but the details hidden behind the shelter walls are crucial to how the rooms perform in an emergency.
Safe rooms are room-size vaults, constructed to be structurally independent from the surrounding walls and ceiling. They can be built onsite or assembled from a kit, but, regardless of construction, these shelters require careful attention from the contractors who are creating them.
Help with standards
The International Code Council is still developing a safe-room standard. In the meantime, though, contractors can turn to a Federal Emergency Management Agency publication, FEMA 320, "Taking Shelter from the Storm," for guidance with site-built safe rooms. (The booklet is available online at www.fema.gov/mit/saferoom.) The document draws on extensive wind testing work done at Texas Tech University, and the accompanying drawings provide construction details for builders, as well as plans that can be submitted directly to local building officials for approval.
The National Storm Shelter Association is a good place to begin for help selecting manufactured products. The Lubbock, Texas-based group was founded in the wake of a series of devastating tornadoes that swept through Kansas and Oklahoma in May 1999. FEMA and the state of Oklahoma provided grants to affected homeowners who wanted to include a shelter in their rebuilding efforts.
"Unfortunately, there were a lot of fly-by-night organizations that came along to take advantage of the situation," says Dorothy Andrake, section chief for risk communication outreach in FEMA's Mitigation Division. The NSSA developed a testing program for manufactured shelters based on Texas Tech's research, and provides a certification label for products that perform to its standards. (Visit www.nssa.cc.)
Whether site-built or manufactured, however, all storm shelters must be able to remain intact in severe-wind situations. Experts say several elements are crucial to meeting this expectation.
Three key factors
- Impact resistance of shelter envelope. A shelter's walls and ceiling must be capable of surviving impact from wind-borne missiles. To prove this performance, the NSSA's standard calls for firing a 15 lb. 2"x4" at the surface being tested – at 100 mph for walls and 67 mph for roofs/ceilings. Additionally, ceilings must be independent of any floor or ceiling above them – so basement shelters cannot be connected to a first floor's joists.
- Wind and impact resistance of door assemblies. "The door is a critical element," says Ernst Kiesling, senior associate dean of Texas Tech's College of Engineering, and the NSSA's executive director. "It must withstand the wind pressure and debris impact." Texas Tech's Wind Science and Engineering website suggests a hollow metal door and frame with 14-, 16- or 20-gauge metal skins (16- and 20-gauge models should be strengthened with a single layer of 14-gauge steel on one side). Hardware should include three heavy-duty hinges and three residential-grade mortise deadbolts.
- Connection and anchorage. "The anchorage is a critical detail that is often slighted or overlooked," Kiesling says. FEMA's drawings provide detailed instructions for ensuring built-onsite shelters are adequately anchored to a cement foundation, so the structure cannot be overturned if directly exposed to severe wind. Manufacturers of shelter kits should include similar instructions for anchoring their products.
Chuck Ross is a Chicago-based freelance writer, editor and web consultant.
| 
)
