The latest building codes and products reduce damage from flooding, wind damage and storm surge
The recovery in Houston and Florida from Hurricanes Harvey and Irma has just begun.
The long-term impact of these massive storms will have on home building in hurricane-prone areas and in the refinement of building codes has yet to be determined.
However, the short-term view is clearer: New home buyers in the future will be more aware of the risks of damage from storms and floods — and builders, building code officials and product manufacturers will continue to work together to create solutions that result in safer homes.
Ed Hudson, director of Marketing Research at the Home Innovation Research Labs in Upper Marlboro, Md., summarizes his predictions: “There is going to be a huge remediation business at first. Capacity will be stretched. This could cause delays if certain materials must go on allocation. Overall, it will put pressure on and constrain building material supply for a while, which could up the price of building materials, which could cause an uptick in the price of housing.”
Codes will be modified and there will likely be a much higher consciousness now for building flood-resistant structures. — Ed Hudson, director of Marketing Research at the Home Innovation Research Labs Eventually, he says, it should also impact building codes. Certainly, building codes became dramatically more stringent following such past major hurricanes as Andrew and Katrina. The 2000 International Residential Building Code (IRC), for example, established a requirement for the use of impact-resistant doors and windows in hurricane-prone areas. In addition, all new homes in areas where wind speeds equal or exceed 110 mph now must meet storm-resistant standards. In Florida, roof straps that connect a home’s roof to the foundation became mandatory in areas where 120 mph winds can be expected.
Subsequent code renditions have addressed load paths in buildings in coastal areas. Codes also require that homes in high-velocity wave action zones be supported on piles, columns or shear walls.
Some 20,000 U.S. communities have already been mapped according to their flood risk by FEMA (the Federal Emergency Management Agency). Recently, Hudson notes, FEMA has expanded these flood zone areas by raising the target elevations, causing builders to build at greater heights and adding more locations that require special construction techniques following the National Flood Insurance Program (NFIP) regulations.
Here are Best Practices for Building in Hurricane-prone Zones
Sound hurricane-resistant building basically addresses three problem areas: lift up from high winds, penetration from wind-blown debris and damage from rain and flood waters. These three best practices for building in a hurricane-prone area will help reduce damage to buildings during storms: 1) tying down the building to its foundation, 2) increase a building’s impact resistance and 3) keeping a building dry by reducing moisture penetration.
1. Tie It Down
There have been huge changes since Hurricane Andrew, agrees Hudson, regarding the strengthening of construction. Many of these are regarding building codes and/or are being driven by the desire to obtain lower insurance rates and are now standard practice.
The revised codes, for example, require buildings in coastal areas to have a continuous load path that directs wind loads on the roof and walls down to the foundation. This has led to widespread use of tie-down straps, J-bolts, cable ties, expansion bolts, hurricane clips and plates.
Other proven ideas to prevent wind damage include strengthening gable ends, limiting roof overhangs, using glue and ring shank nails on roof sheathing, taping sheathing seams, following recommended connector size and nailing patterns and extending fascia boards below the soffit of overhangs. Storm experiences have also shown that a one-story home with a moderately sloped hip roof featuring baffled and soffit ridge vents will fare best against high winds and wind-driven rain.
A more recent innovation in tie-down products, says Hudson, is the new truss screw with fully-threaded shanks for fastening trusses and rafters to top plates as an alternative to hurricane clips. The screw is used for stud-to-bottom plate connections as well. Likewise, the Hardy Frame Shear Wall System from MiTek uses panels and moment frames to resist lateral loads from wind forces.
There is also recent growth in popularity of taller sheathing panels. “In hurricane areas,” Hudson explains, “there has been a departure from standard 8-foot wall sheathing and increasing acceptance of 9- and 10-foot panels that span from the bottom of the wall plate to the top of the wall plate, making construction faster and eliminating possible moisture penetration at the former seam.”
The use of spray polyurethane foam has also become more popular, Hudson adds. “When you spray it on the underside of the roof, it seals the roof from air penetration and acts as a glue,” he says. “It’s claimed to help keep the roof system from blowing off in a storm.”
2. Make It Impact Resistant
Reinforced, impact-resistant doors, laminated windows, storm-resistant windows or hurricane shutters, pull-down PVC shutter systems and high-impact synthetic window shades all contribute to a home’s impact resistance.
Advanced framing systems with two-by-six wood studs (24 inches on center), combined with structural panel sheathing, adds strength to walls, as does high-density wallboard with embedded mesh. USG’s enhanced wall panels, for example, offer up to five times the impact resistance of regular wallboard. Garage doors are a particular weak point. It’s recommended that this type of doors should be braced to withstand a maximum wind speed of 180 mph.
FEMA rates impact-resistant products as those that can survive having a 12-foot two-by-four being shot at them at 100 miles per hour.
Precast concrete wall systems, says Brian Bock, vice president of Sales & Marketing at Dukane Precast Inc. in Naperville, Ill., can easily pass the FEMA impact test. Dukane builds homes using a precast concrete double-wall panel system featuring exterior and interior layers of reinforced precast concrete sandwiching a layer of R-19 insulating foam. The firm has also constructed homes under the Insurance Institute for Business & Home Safety (IBHS) FORTIFIED for safer living program.
Dukane has demonstrated the impact resistance of its precast walls by shooting two-by-fours up to 135 mph at wall sections. The projectiles simply bounce off the precast walls. “We also shot two-by-fours at sections of both a typical vinyl-sided, wood-framed wall and a conventional brick wall,” says Bock. “The two-by-fours easily penetrated each of these.”
3. Keep It Dry
Sealants, waterproof membranes, house wrap, rainscreen systems and use of mold and mildew-resistant materials can keep rain and moisture out of the home or reduce resulting damage.
Building for fast recovery from flood waters is also possible. This requires designing the home to minimize flood damage by reserving the home’s lower level for parking or storage only. FEMA has published guidelines for on-grade breakaway walls to surround these “open” lower levels that wash away in a flood. Resilient building also calls for the use of mold-prevention building techniques that can get wet and dry easily, such as using concrete walls and open web floor trusses.
One recommendation from the IIBHS resilient home program, says Hudson, is to prohibit water penetration into the home in the event the roofing blows off by creating a seal beneath the roofing using a self-adhesive ice and water shield on the roof deck and by taping underlayment seams with flashing tape.
All-in-one weather barrier and structural sheathing systems, such as the ZIP System from Huber Engineered Woods, have gotten a lot of recent attention, according to Hudson. “With this product, the water-resistant barrier is attached to the sheathing,” he explains. “It won’t blow off. You simply tape the seams.”
A proven way to protect a home from extreme flooding — short of constructing a waterproof wall or sand bagging a home’s perimeter — is to build the home on stilts, pier foundations or on a raised platform.
Topsider Homes in Clemmons, N.C., builds pedestal, stilt and piling homes designed to be resistant to tropical storms, hurricane force winds and storm surge. The homes are both elevated and multi-sided in design, which allows storm and hurricane winds to flow around, over and under them.
How Harvey and Irma Might Affect Homebuilding
No one yet knows what building system innovations, code changes and design concepts that address flood disasters may result from Hurricanes Harvey and Irma.
Harvey may, indeed, change how we build in coastal areas, concludes Hudson.
“Codes will be modified and there will likely be a much higher consciousness now for building flood-resistant structures,” Hudson envisions. “But the broader effect will be felt on the overall construction industry. Harvey (and Irma) is going to have a national (effect) on construction prices, schedules, material availability and labor availability.”