The lessons of Hurricanes Ike, Gustav, and Katrina — Gulf of Mexico storms where surge flooding, rather than wind, was the dominant cause of damage — were a major focus of interest at this spring's 2010 National Hurricane Conference in Orlando, Florida (March 29th - April 2). Ike's destruction, in particular, drove home the point that storm surge and waves have the power to devastate whole communities, even when storm winds only draw a Category 2 rating. But there's no practical way to engineer a building to handle the impact of a wind-driven ocean wave — if, says coastal engineer Chris Jones, "we want to live in houses that look like houses. We could build bunkers that would survive, but then it's not a house." Coastal building codes handle the risk using elevation: they call for piling foundations that raise houses above the 100-year Base Flood Elevation (BFE), defined as the height that flooding has a 1% chance of reaching in any given year, according to computer models. But Ike also taught that being at or above the BFE is no guarantee of safety. In Ike, average flood water depth appear to have gone several feet above the official BFE, and waves crests evidently rose even higher than that. In coastal Texas, where sea levels have been rising, ground has been subsiding, and meteorological data involve some guesswork, the flood maps certainly understated the actual performance of Hurricane Ike. A post-Ike assessment team sent in by FEMA found examples such as this: A house five feet above the BFE that avoided damage next door to a lower house that had been badly damaged. (The full, 444-page report, "Hurricane Ike in Texas and Louisiana: Mitigation Assessment Team Report, Building Performance Observations, Recommendations, and Technical Guidance," is available from FEMA; and in a Google Books version.) On the Bolivar Peninsula beach front, a row of homes built to above-code standards in the Institute for Building and Home Safety (IBHS) "Fortified" program survived Ike's surge, standing as lonely examples on an otherwise bare shore. The first occupied floors of these houses, at 27 feet above sea level and about 20 feet above grade, were 10 feet above the official local Base Flood Elevation. Four of the five homes survived (the fifth, evidently, was destroyed when floating debris from a nearby house struck the pilings). But storage decks attached to the homes' piling foundations, just above the BFE, were ripped away by the waves. At the Orlando conference, IBHS engineer Tim Reinhold told the Houston Chronicle, "We don't think the 100-year flood plain is anywhere near close to being high enough to build to. Our thinking is that the 500-year flood plain should be the minimum."(" When is 20 feet not high enough?" by Eric Berger) But it's one thing to advocate building a little bit higher within the 100-year flood plain; it's something else to advocate expanding the boundaries of the flood plain itself. On the Galveston, Texas, beachfront where Ike made landfall, the 500-year base flood height is about six feet higher than the 100-year base flood elevation. In other places along the Gulf and Atlantic coasts, says Chris Jones, the 500-year and 100-year flood elevations might only be a foot or two different. But there's also the horizontal dimension to consider: along the Texas coast, the footprint of that 500-year flood would extend inland, possibly for miles, into the state's flat coastal counties. Imposing flood-resistant construction requirements, and a mandate to carry flood insurance, into that new territory might be a politically impossible feat. Like many decisions, elevation decisions may come down to dollars and cents, as well as an estimate of risk. Changing a foundation design from a perimeter stemwall, which cannot handle wave impacts, to an elevated piling foundation that is able to withstand floods and waves, is a costly measure, Chris Jones points out. But if you're already in a V Zone where pile foundations are required, the cost of changing the design to raise the first floor may be manageable; rule of thumb for a house on pilings, Jones says, is that it costs about $1,000 to raise the house by a foot. "And by going up," Jones notes, "not only are the owners decreasing the chance that their building will be damaged or destroyed, but they are also decreasing their flood insurance premiums. And if you elevate three or four feet above the BFE, you will cut your flood premium at least in half — maybe two thirds."