Understanding Hurricane Resistant Home Construction: Part One

The Seaside Dream Window View

In light of the unfortunate storm devastation to impact our coast as well as the beloved Keys and islands in the Atlantic and Caribbean, I felt compelled to shed some light on our process when building our homes for the potential impact of a hurricane. Our thoughts and prayers are with all of those impacted by the 2017 season.

Protecting a most important investment may come with a cost, but not protecting it can be even more costly in the long run. There are some “extra” steps that may be taken to protect your home that when taken, may help ensure that your investment withstands the harshest tests of Mother Nature.  Storms know nothing about lines and boundaries, and while we can utilize building code required designs, as implemented to proactively mitigate storm damage, there shall always be structural shortcomings during a real time, real world event; therefore, I do believe it is important to “err” on the conservative side of things, and exceed certain building code requirements where it seems to be most practical.

I will offer some general suggestions that I have maintained to have value for wind borne mitigated construction practices. Having lived and worked in the Florida Keys and many other Florida coastal and inland cities, building homes throughout these regions for over forty years, I have chosen to utilize many products and practices that have become my own “minimum code standard”, which often exceeds the Florida Building Code requirements. From client testimonies, time has shown that these have offered a much higher value to them than what the initial investment incurred. Many of these features offer advantages that speak to lower maintenance in general, storm protection alone notwithstanding, as there can be value added benefits that enhance one’s lifestyle beyond just storm preparedness.

At each step of the process, certain things can be done and used which will ensure that the integral system of the home’s structure is enhanced. A systemic approach is thus considered when looking at the bigger picture, and each step of production can be improved. All the while we are sure to weigh cost vs. benefit on a case by case basis. These shall include extra attentions to the homes foundation design, exterior wall composition, roof and truss design, truss strapping, exterior waterproofing materials, window and door installation techniques, and a range of miscellaneous products which through both material composition and design, have proven to hold up well is harsh coastal environments.

Structural Design in General

When building a home within a hurricane prone region, builders must use engineered home designs that meet a specific building code requirement for the “zone” in which they are building.  It may be obvious that the insurance industry has a major interest in lobbying the Code Development Board to build to the highest standard. These rules are very important to follow of course, but it is also important to understand that these restrictive codes are developed considering many factors. While most of these factors have basis in engineering sciences, in statistical analysis, wind studies and the like, it is also true that financial feasibility is a true and very real consideration, and becomes a major factor during code development; the economics of building costs vs. affordability must be seriously considered.

Building the strongest of structures can be very expensive to construct. Code Development Board members are also subject to pressures from special interest groups, who see demographic statistics, and who wish to promote the ideal that the “American Dream of Homeownership” is not only available for the wealthiest constituents. In Florida, the highly respected Construction Industry Licensing and Board, which also oversees code requirement development, is also charged with making sure that these codes are not too highly constrictive and prohibitively expensive.

Therefore, these codes can be based upon a minimum standard, albeit that they must also respect the needs for safety, and with deference to using basic common sense as it applies to wind storm mitigation. It is true that the most restrictive coastal zones use the highest standard; however, since these zones are often waterfront properties, it stands to reason that only the wealthy can afford building there anyway. In those cases, the structures built within those zones are engineered to the highest of safety standards. However, this does not mean that some of these techniques cannot be used on lesser zones.

I believe it is practical to look at the products a builder can use for all the home’s he builds, regardless of the zone a structure may be built in. I think it can stand to reason that a hurricane has no brain, and therefore such a storm event can and will often negatively affect structures which lie more inland, just as they create issues for those structures built on the coast…a storm knows no boundaries, and it cares not at all about statistics. It’s hard to argue that one can ignore a home’s vulnerabilities to potential storm damage no matter where a home may sit in a hurricane prone state.

There are some general suggestions that can be made across the board. These will include features and practices that affect a home’s foundation, its exterior envelope integrity (walls, roof construction, finished roofing, aperture devices (windows and doors) and other exterior finishes. Regardless of the level of interior finish, monies spent on these most important exterior features will ensure that a home can become a family heirloom that firmly holds up to the harshest weather conditions.

What we are up against

A project starts with property preparation and foundation design; but before we consider the dynamics of actual construction, let’s first look at what we are up against.

Think of the center of a tropical cyclone acting as a vacuum cleaner’s hose. If one passes a shop vac hose opening at 90 degrees to be just above the surface of a bowl of water…an actual column of water rises toward that opening, creating a lifted area that can be equal to the diameter of that opening….and even beyond that as the water slopes and tapers away. Now imagine this hose opening to be 15 miles across. This raised body of water then will create a base “surge” in the height level of the water…sort of like a flat wave base that is 15 miles across in this example. Now on top of that raised column of water, we also have surface waves created by the wind once we leave the clam of the storm’s eye. If a raised surge “bowl” is let’s say 8’ high, and then there may be 8’ high waves that add to that height once the eyewall is penetrated radiating outward, then we might have a 16’ high force of destruction that can do almost unimaginable things to a coastline, much less a structure that sits there. As the water and wave actions “move in”, this slow moving tidal wave scours the coast with an almost unimaginable force. Once it moves away as the storm continues to pass, the receding water once again scours the coast in the opposite direction. This is one of the reasons that building codes have changed so dramatically for structures built along Florida’s coastline and why it is only the wealthiest of homeowner who can afford to build there.

Along the coastline there is a “demarcation” line called the CCCL line. This Coastal Construction Control Line is set by the Army Corps of Engineers, and passing over this line to build a new structure requires a completely different type of foundation. To combat scouring, one must use one of a few different types of pilings that are basically subterranean “stilts” that descend into the soil, underneath a reinforced concrete and steel grade beam foundation that ties each pile cap together so they can support the home above. The theory is that as the wave actions and storm surge forces scour the sand, removing it completely, the home will theoretically remain stable and sound, as it eventually sits above the action of surface erosion. In addition, and in conjunction with this approach, the concrete slab and the first level exterior walls, if there are any, must be designed in some cases to be “frangible”… a fancy term for “breakaway”…. engineered systems. These are not tied to the foundation, rather they are set apart and independent, so that the water can scour those away without enabling the forces of the water to take the rest of the structure above and below with it.

It is true that if one is not building a home that transcends the CCCL, that the requirements are more relaxed, and thus a home may be more affordable. But there are other sub zones along the coast that also affect a structures design that still add costs to the home. These are referred to as Zones “A” through “D”. The rule of thumb is that the closer you are to the ocean, or any other large body of water, the forces potentially increase and so does structural vulnerability.