hurricane damage

Designing to mitigate hurricane losses

As we enter into hurricane season, many people ask, "How can I build to mitigate hurricane damage?" Historically, we have worried more about hurricanes with high winds but Hurricane Florence proved that category 1 storms can be just as disastrous. Eight people in South Carolina died, property damage was over $607 million, and more than 2,000 homes were lost to flooding.

When building a new house there are three critical concerns in the design and construction in hurricane prone areas that address the simultaneous impacts of wind, rain, and flooding.

Keep the building from blowing away

The building must be tied together from the roof rafters to the foundation. The most common method employs hurricane clips and tie rods. The building must be designed to withstand wind shear which can be accomplished with plywood sheathing if there are limited amount of openings in the walls. Walls with large openings often require steel framing to withstand the wind shear.

Windows and doors need to be protected from flying objects. The simplest but not the cheapest is to install impact rated windows and doors. Other options include hurricane rated shutters, PVC coated woven fabric such as Wayne Dalton’s Fabric-Shield® or plywood panels cut to fit the openings and fastened as per the building code.

The exterior finishes should be rated to withstand hurricane force winds and be installed securely to the structure as per the manufacturer’s recommendation to meet the tested installation.

Keep the rain out

Keeping rainwater out of the building is fairly straightforward but only if design decisions are made to address it. As the building scientist William Rose observed, “If it doesn’t get wet…it can’t leak.” Thus, large overhangs help keep the building dry by reducing the amount of water flowing down the walls by a minimum of 50%.

Field experience shows that water leakage around doors and windows is very common. Therefore, sill pans and flashing are essential. Flashing has two distinct purposes; it keeps water from getting into the wall through joints and it guides water back out of the wall when some leakage does occur.

All exterior cladding will allow some moisture to pass through. The best way to capture the water and direct it out of the wall system is with a drainage plane which is a waterproof layer on the exterior of the wall sheathing. For the drainage plane to work correctly there is an air gap to promote drying. Likewise, a secondary roofing membrane will keep water out if the primary roof material is compromised.

Crawl spaces must be sealed against water leakage, humid air infiltration and vapor permeation from the earth. Closed crawl spaces do not have vents to the exterior. They are insulated at the perimeter wall.

Drain water away from house by using gutters and sloping the ground away from the building.

Prevent flood damage

The most important consideration is to elevate the structure and mechanical systems to minimize its contact with flood water and a potential storm surge. The new flood maps that will soon be adopted in Beaufort County are lowering the flood heights in many areas. It may be prudent to place your house at the current higher requirement because of rising sea levels.

Crawl spaces located in a flood zone need hydro-static vents to prevent flood waters from collapsing foundation walls. The hydro-static vents will allow flood water to enter and exit the crawl space. Charleston based Flood Flaps® provide a tight seal for a closed crawl space.

Finally, use materials that tolerate soaking and can easily dry.

 


The Case for Resiliency

weather and climate disaster map
Credit NCDC.NOAA.org

According to NOAA, since 1980, the US has sustained at least 241 weather and climate disaster where the overall damage exceeded one billion dollars. Hurricanes are a combined 919.7 billion in total damages with an average of 21.9 billion per event. The other natural disaster in order of costs are drought, wildfires, flooding, freezes, winter storms and severe storms. The South and Southeast regions experience higher frequency of billion dollar disaster than other regions. In 2018 natural disasters cost the US $91 billion dollars.

resiliency coastal

Despite the evidence – we are ignoring the consequences of building in vulnerable places.

According to the National Institute of Building Science's research found that mitigation funding can save the nation $6 in future disaster costs, for every dollar spent on hazard mitigation. They also demonstrated that investing in hazard mitigation measures to exceed select building code requirements can save the nation $4 for every dollar.

They estimated that implementing these two sets of mitigation strategies would prevent 600 deaths, 1 million nonfatal injuries and 4,000 cases of post-traumatic stress disorder.

flooding resiliency

Resiliency is similar to sustainability but there is a difference. Sustainability is reducing a building’s impact on the environment and resiliency is reducing the environment’s impact on a building or community. Generally, sustainability initiatives are add to a building’s resiliency but some resiliency requirements are not as sustainable, especially when they are creating redundancy.

resiliency from hurricane

Resilience is about surviving and thriving regardless of the challenge, whether it is a chronic stress or an acute shock. Chronic stresses weaken the fabric of a city on a day-to day or cyclical basis. They include issues such as global warming, poverty, homelessness and aging infra-structure. Acute shocks are sudden sharp events that threaten a community. Often acute shocks are weather related but they can also be human induced such as an act of terror.

Four Kinds of Resiliency

Climate Resiliency

vulnerability to sea level rise map

Architect, Lance Hosey identifies four kinds of resiliency. The first is Climate Resiliency which is reducing the environment’s impact on the building. Depending on the anticipated hazard buildings and landscapes may be protected or hardened against the elements to withstand hurricanes, floods, and fires. Other options include adapting or retreating.

In the case of rising sea levels the options of protecting is building levees or other “hard” methods, accommodating would be raising structures or using “soft” or natural protection measures such as wetlands restoration, and finally retreating would be accomplished by moving or demolishing flood-prone buildings.

This is a huge issue for us because the southeastern US alone represents nearly 70% of the entire projected populations at risk.

Functional Resiliency

The second is Functional Resiliency.  This includes the systems where the building is still habitable and functions. Current standards and codes focus on preserving lives by reducing the likelihood of significant building damage or structural collapse from hazards But they generally don’t address the additional need to preserve quality of life by keeping buildings habitable and functioning as normally as possible, what we call ‘immediate occupancy.

Community Resiliency

The third is Community Resiliency which focuses on municipal and neighborhood resources that help people bounce back to normality or better.

The National Institute of Standards & Technology’s Community Resilience Planning Guide for Buildings and Infrastructure Systems (Guide) provides a practical and flexible approach to help all communities improve their resilience by setting priorities and allocating resources to manage risks for their prevailing hazards.

Aesthetic Resiliency

The fourth is Aesthetic Resilience which is best described by the Senegalese poet Baba Dioum, “In the end, we conserve only what we love.”