Rebuilding in Tornado Country

first_img Fine Homebuilding: Energy-Efficient Framing Practices for Hurricane and Tornado Country Fine Homebuilding: Homes Can Survive TornadoesGreensburg’s Recovery Saga Gets GreenerA Heartland Approach to Energy EfficiencyGreen Basics: Insulated Concrete Forms Building Resilience for a ‘Close Encounter’ with DisasterMartin’s Ten Rules of Roof Design Tornadoes have struck the Midwest with a vengeance this year, killing dozens of people and causing widespread destruction of property. In the city of Moore, Oklahoma, a tornado with winds topping 200 miles per hour struck on May 20, reducing whole neighborhoods to rubble.Many homeowners will rebuild, so what should their new houses look like? In a post at GreenBuildingAdvisor’s Q&A forum, David Gregory raises that question.“The likelihood of another direct hit is tiny,” Gregory writes “The biggest opportunity is improvements in comfort and reduced energy consumption. But durability, I’m sure, is on people’s minds, while costs are, of course, an issue.”Questions that Gregory finds important concern the design and construction of tornado safe rooms, construction details for roof overhangs, the costs and benefits of roll-down metal shutters to protect windows, and whether attics should be vented or unvented.“I wanted to tap the collective intelligence to work through how to build back better (or retrofit surviving homes for resilience), both in terms of ‘what’ and ‘how’ — especially, to discuss what is locally appropriate and cost-effective, specific technical resources, etc., given the unique and extreme conditions in Oklahoma.” Reinforcing wood-framed buildingsPatrick Walshe says that if homeowners decide to rebuilt with wood because concrete is too expensive, there are a number of ways to reinforce the structure.“Our house has the Simpson tie-down metal straps on the rafters and between the stories,” he writes. “There are 3-in. metal plate washers on the anchor bolts fastening the house to the slab as well as some heavy-duty metal brackets connecting studs to some anchor bolts. The house was built with pre-made stud panels sheathed with plywood. This plywood overlaps adjacent panels and the second floor in a jigsaw fashion. The design limited expanses of windows to allow enough shear strength in each wall.”In addition, he adds, the architect insisted that nail heads be flush with the plywood, not set below the surface. Double-stud walls are set on 2×10 plates and have 2 inches of Roxul insulation on the outside to make them stronger and to increase resistance to penetration by windblown objects.Hurricane ties between the rafters and wall framing, adds Dana Dorsett, “keep the roof from flying off in one piece.“Construction adhesive between the rafters and roof sheathing and tighter fastener spacing keep the sheathing from popping off a sheet at a time,” he adds. “If the wind strips the deck bare of roofing and foam, that’s a much cheaper repair than the whole roof (or whole house).” Tapping online resourcesGBA senior editor Martin Holladay, Lucy Foxworth, and Trevor Trainor point to a number of Web resources that can help people decide the specifics of rebuilding their homes.Among them:Information published by the Federal Emergency Management Agency (FEMA) about safe rooms.“Tornados of the South: Structural Performance of Newly Constructed Homes in North Carolina, Alabama, and Georgia,” at the web site of APA — The Engineered Wood Association. The download is free, Foxworth says, after completion of a simple online registration.An article about manufactured safe rooms from The Journal of Light Construction (to download the article, it looks like you’ll need to subscribe).A free article from JLC about code requirements for safe rooms.Recommendations from the Insurance Institute for Business & Home Safety. Reinforced concrete structures resist tornado damageDana Dorsett suggests concrete walls and roofs reinforced with rebar would probably be able to resist just about any tornado structurally. “But,” he adds, “you’d still have to replace all the blown windows and doors, and some or all of the siding and exterior insulation, depending on the severity of the storm.”Code minimums for a concrete wall assembly in Oklahoma would require continuous exterior insulation rated at R-5, he adds, would easily be met with just 1 in. of foil-faced polyisocyanurate. Installing 1 1/2 in. of the insulation would bring the performance of the wall assembly up substantially “for not a huge uptick in cost,” Dorsett says.“How building with reinforced concrete compares to timber-framing costs depends on the costs of concrete and the cost of labor in that area,” he writes, “but for most homes in most markets it doesn’t rise to a double-digit cost adder to the project as a whole.”Mike Collignon, like Holladay, thinks walls built of insulated concrete forms (ICFs) would be a good way of guarding against tornado damage, although Collignon concedes that some homeowners will be scared off by the increased costs of building that way.center_img Taking a lesson from GreensburgOne model for post-tornado reconstruction comes from Greensburg, Kansas, a community of 1,400 people devastated by an extremely powerful tornado in May 2007.Thanks to emergency warnings about the approaching storm, casualties were kept to a minimum. Even so, 11 people were killed and 90% of the town’s buildings were destroyed by the 1.7-mile-wide tornado.The people of Greensburg decided to rebuild their town as a model green community, and their efforts were later described in a GreenTour Book. The rebuilding effort also is described in a report by the Building Science Corp., which was hired to help design replacement houses and train builders.Foxworth says some of the BSC recommendations for rebuilding are “a little surprising.”“They recommended building with 2×6 advanced framing with OSB shear panels in the corners and insulated foam sheathing elsewhere,” she says. “I thought foam sheathing was not a good barrier to windblown objects in tornado-prone areas.”No, Collignon says, foam sheathing is not much of a barrier to windblown objects unless “it is backed with something of significance, like Kevlar or concrete.“I’ve personally witnessed 2x4s fly right through brick veneer/batt insulation/frame construction during wind-cannon testing, and the speed of the stud was only simulating an EF-1 tornado (110 mph wind speed, 60 mph stud speed,” Collignon writes. “Foam insulation in that instance wouldn’t have fared too much better, in my opinion.”He adds, however, that he’s seen a video clip in which an ICF box built to simulate a closet was subjected to a TNT blast from only 6 ft. away. “There were areas of compression and minor burn marks on the foam,” he says, “but that was the limit of the damage.” RELATED ARTICLES Our experts’ opinionsHere’s what GBA technical director Peter Yost had to say:Martin and others have done a great job covering the issues and providing resources. I just have two perspectives to add:With support from the Lawrence Berkeley National Lab and the Department of Energy, BuildingGreen has been developing a window-covering website and selection tool. One of the coverings included in the resource is roller shutters. While not inexpensive, these shutters have a significant impact on energy efficiency and storm protection of windows. Check out the purchasing section of the site for qualifying roller shutters.Alex Wilson, founder of BuildingGreen, Inc. recently created the Resilient Design Institute and adds his perspective:The Resilient Design Institute recommends that safe rooms be installed in all new homes as well as existing homes undergoing major renovations in the parts of the country most vulnerable to tornados (red area in the FEMA wind vulnerability map). Guidance on building safe rooms is available from FEMA. In most of the country (all shaded and cross-hatched areas of the FEMA map), wind resistance should also be provided in home construction (for example, hurricane straps); in these areas, RDI recommends building to the Miami-Dade County Hurricane Code or its equivalent.last_img

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