PATH - A Public Private Partnership for Advancing Housing Technology
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Building to Withstand the Big Storm
Hurricanes, tornadoes, and lesser severe storms can cause tremendous destruction. But there are existing, affordable building practices that can minimize--and sometimes eliminate--the damage normally associated with such weather events. If you are building in an area that experiences catastrophic storms, why not at least consider the best practical storm-resistant design?
Poured Concrete Homes
In preliminary studies, PATH partners are finding that poured concrete homes resist wind loads better than concrete block homes, with the additional benefits that poured concrete homes are faster to construct, require less onerous inspections, and provide a more easily installed, uninterrupted, thermal barrier of insulation. The team is now examining how to exploit the solidity of poured concrete walls to enable homes to weather a major storm with hurricane-force winds.
PATH teamed with Mercedes Homes, the Federal Emergency Management Agency (FEMA), the University of Florida, and Fannie Mae to develop a new standard in hurricane-resistant construction. This project, located in Melbourne, Florida, was built on earlier work by the Consortium for Advanced Residential Buildings (CARB), one of DOE's Building America teams.
Now in the process of finalizing its upgrade recommendations, the team finds that the Mercedes poured concrete homes require a surprisingly small additional investment in the wall system to withstand the 125 mph wind force goal established by project partners at the University of Florida. Design protocols call for extra tie-downs and alignment of the bearing walls with the truss tie-down points to create a direct load path configuration. Including the extra tie-downs in the design and coordinating the alignment are essentially planning issues. So the minimal material adjustments represent less than $10 in additional costs. Similarly, additional steel costs about $13, primarily for reinforcing around windows and sliding glass doors. And with another nominal increase in cost to cover a deeper reinforcing member, the wall system could withstand 135 mph winds.
Protecting Roofs and Windows
PATH is finding that 7/16" OSB (oriented strand board), commonly used in Florida, is adequate for the 125 mph goal, and that the nailing pattern specified by existing codes is also adequate for wind loads.
Costs for roofing enhancements and removable steel shutters are somewhat higher, but not prohibitive. Shutters for a 2,400 square foot single-story home with 312 square feet of windows run just under $700.
Roof covering is the real issue, as asphalt or fiberglass shingles often blow off during a storm and expose the sheathing underneath to wind and water. The seams between the deck sheathing allow water to enter the home, even when the entire roof structure is intact. The best defense options are a new roof shingle with a 130 mph rating and rubber or asphalt sheets with peel and stick undersides, also called self-adhering polymer modified bitumen underlayment, for secondary water resistance. Applying strips of these rubber or asphalt sheets only to the outside joints of the roof decking can effectively seal the joints at less cost than covering the entire roof, and greatly reduces water leaking into the home after the roof covering has been lost or damaged.
Building, Selling, and Financing
PATH hopes to encourage the wider use of poured concrete. Poured concrete is a viable option anywhere slab-on-grade houses are built, with the exception of high seismic areas. Laminated rigid foam insulation inside of the poured concrete offers an unbroken thermal layer. Assuming the attic is appropriately sealed and insulated, the homes are virtually airtight. Although more wind-resistant and faster to build, poured concrete homes are sold at the same prices as traditional concrete block houses.
The goal of the PATH/FEMA/Mercedes project is not only to demonstrate mitigation strategies and technologies, but also to help create an incentive for the adoption of these technologies through reduced homeowners insurance premiums. The PATH team is working with the Tower Hill Group in Florida to secure a premium reduction on homeowners insurance for homes that incorporate these hazard mitigation design protocols.
Follow the project chronology to track PATH's final recommendations.
For additional information on poured concrete construction, contact the Concrete Foundations Association and the Concrete Homes Council, or consult the Concrete Homes Web site.
Content updated on 3/8/2006
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