An average house can usually withstand wind speeds of about a 100 mph, or 110 mph if located in an area where strong winds are a common event. Several companies are constantly testing materials and construction techniques and as of today a highly engineered house designed to resist hurricanes can withstand wind speeds up to 185 mph. By analyzing different types of houses, we can get a rough idea of how resistant to wind that type of house is:
- Concrete house
- Masonry, Brick or Cement Block house
- Wood frame construction
- Manufactured or mobile homes
- Modular homes
Even if we decide to build a concrete house instead of a wood frame one because the material has a better resistance to strong winds, there are other important factors we need to consider to get an approximate idea of how much wind the house can withstand. The Shape of the Building and the roof design have a big impact on the house resistance to high winds, moreover and often disregarded, the site where the house is located can increase or decrease the structure’s performance and needs to be regarded when estimating how much wind speed a house can withstand.
Analyzing different types of houses to get a rough idea of how resistant to wind that type of house is
Concrete houses are one of the most resistant houses in front of strong winds
They are strong, and robust enough to withstand the damaging impact of most flying debris, one of the greatest’s danger during hurricanes and tornadoes. The strength of concrete houses is often made obvious after catastrophic events such as the 1992 Hurricane Andrew and the 2012 Hurricane Sandy during which several concrete homes survived the damages while neighboring houses built with other materials where completely destroyed . Given the evidence, some builders of hurricane-prone coastal areas are offering concrete homes advertised as stylish and stormproof .
Ensuring the protection of the whole house to extreme winds can be extremely expensive and difficult, so the Federal Emergency Management Agency (FEMA) recommends to build either a shelter or a safe room in those areas where hurricanes and tornadoes are common. One of the approved materials for these safe rooms is reinforced concrete due to its great wind resisting performance . Some buildings due to their vital functions, need to ensure the safety of the whole building and a Missouri Hospital has proven successful. The St. John’s Regional Medical Center achieved to build a “storm-hardened” shell with precast concrete after having suffered from terrible damages during a devastating tornado .
While concrete is the material with a higher chance of resisting devastating winds, and debris impacts, a concrete building can also be damaged and it is especially vulnerable to heavier and solid flying debris that could impact the walls with extreme speed and strength.
Masonry, Brick or Cement Block house is almost as wind resistance as a Concrete house
It is possible for this kind of construction to be pretty much as strong as concrete building, but only when done following certain requirements because the strength of a brick wall depends entirely on the construction method. For a brick house to hold a firm resistance to strong winds, the walls should be thick, ideally up to four bricks thick and built in interlocking patterns . However, to ensure a similar resistance to that achieved with concrete, they should be reinforced with steel bars. FEMA includes reinforced masonry walls, together with reinforced concrete in the requirement to build safe rooms and shelters .
Reinforcing masonry is especially important because masonry alone is only strong vertically, it can support a heavy weight but it is very weak in front of a horizontal force such as the one coming from the wind. Reinforcing it gives masonry this additional flexibility feature that allows it to withstand strong winds. Moreover, in order to ensure the efficiency of the reinforced brick wall it has to be well anchored to both the foundation and the tie beam. Most of the masonry construction failures aren’t a direct cause to the material itself but due to a lack of anchorage .
Figure 1. The importance of anchoring the wall from foundation to roof.
There are a number of homes that appear to be brick structures since the outside look of the house is that one of a brick house but their structure is built of wood framing. The wall finish of these houses is done with brick veneer, a much thinner brick which only purpose is aesthetic. These kind of houses give the impression of a heavier and stronger masonry construction but need to be analyzed as wood frame construction since that it’s their main structure.
Wood frame construction can with the right setup be as strong as a common brick built house
While wood frame construction is the cheapest and most common building technique for American houses, it isn’t naturally strong in front of the strong winds caused by hurricanes or tornadoes. However, according to FEMA wood frame houses built in accordance with the IRC building codes performed well structurally during the 2004 Hurricane Season .
While wood lacks the robustness of concrete or reinforced masonry, it is very flexible and strong, two very desirable qualities to withstand strong winds. To ensure these characteristics it is key to choose the right wood and the Florida Department of Community Affairs (DCA) recommends the usage of Yellow Pine since it matches the requirements and can withstand 150 mph winds . Yet, despite of the strength and flexibility offered by this material, one of the biggest dangers of hurricanes and tornadoes is the impact caused by flying debris and a traditional wood frame wall is not designed to withstand these impacts.
While these kinds of houses aren’t close to the strength that concrete or reinforced masonry can offer, when properly designed can perform well enough. It is especially important to pay attention to execution since the most common failures associated with wood frame houses are loss of roof sheeting due to inadequate nailing or bracing .
Figure 2 Sheet metal straps, brackets or wood cleat to tie roof-framing to timber walls
Figure 3. Extra bracing with a continuous diagonal timber brace nailed to wall studs, joist and rafter
Manufactured or mobile homes suffer the most damage in a storm
Mobile homes have a bad reputation withstanding strong winds, and while these constructions used to suffer the most damage some years ago, the federal Manufactured Home Construction and Safety Standards (MHCSS) has done a very good job in the past years.
We tend to confuse mobile and manufactured homes, but the MHCSS clearly separates these two and defines mobile homes as those houses built before June 15, 1976 the date when the HUD building code was stablished, since after this date all manufactured homes were built after very strict standards of safety . Therefore, mobile homes are not designed to withstand strong winds and perform poorly during hurricanes and tornados, even when not very extreme.
Even if in 1976 the HUD was regulating the construction of manufactured homes, it wasn’t until 1994 that the regulation updates became stricter with wind resistance and started classifying manufactured homes into three different zones according to the expected wind speed of the area . Thanks to the industrialized construction process and the strict regulations that these houses are required to stick to, we can tell how much wind speed a manufactured home can withstand. Every manufactured home, built under the HUD code has a Data Plate describing the wind Zone to which the house is built. Those built up to Zone II standards can withstand wind speeds of up to 100 mph; and Zone III houses can withstand wind speeds of up to 110 mph. Those houses without a data plate or built before 1994 are classified under Zone I and are considered to perform poorly during strong winds .
Modular homes have advanced engineering in wind resistance
Modular homes are often confused with manufactured homes due to the fact that they are both built in a factory-like setting; though that is the only thing they have in common. Modular homes follow as well an industrialized process of construction but are designed to be permanently placed on solid foundations and required to stick to the same building codes and requirements as any site built home.
Modular homes have a big advantage in front of site built though, since the process of construction is conducted in a factory-like setting, the advanced engineering building techniques together with the benefits of being in a controlled environment, ensure that the homes are built up to the specifications recommended by the state and local building codes .
However, modular homes can be built of a variety of materials, structures and shapes. If you are planning to build in a location where hurricanes or tornados are often, it is recommended to build your modular home with a modular home manufacturer experienced in these situations such as Florida Modular Homes (FMH) .
Shape of the Building and the roof design
Shape has a strong impact on how well a house performs during strong winds. A symmetrical, compact, round, or even hexagonal house will show the best performance during hurricanes or tornadoes. Aerodynamic shapes help deflect the air flow around the house reducing the wind pressure . The houses with a better performance apply aerodynamic shape on both the house structure and the roof, and while a dome shaped house is maybe the first image that comes to mind, there are multiple ways to achieve these aerodynamic shaped houses.
Figure 4. A Dome as the ideal Aerodynamic shape
Figure 5. Hip roofs geometrically designed with slopes in at least four directions.
The company Deltec homes has engineered a hurricane-proof house construction that has withstood past very damaging hurricanes including Katrina and Sandy . One of the reasons behind the success of these houses is their shape, a smart round shape. This aerodynamic design, together with a reinforced roof allows the house to withstand winds up to 185 mph .
Figure 6. The aerodynamic shape of a Deltec House
The site where the house is located can increase or decrease the building’s performance
The natural surroundings of the house will influence the behaviour of the wind by either protecting the house from its direct influence or by increasing the wind pressure to which the house is exposed.
- Natural windbreaks: A house that is placed by a forest, a small hill or any element that can slow down the wind will be protected from it and the pressure of wind that the structure will receive will be much lower .
- Funnel Effect: Narrow valleys create a funnel effect increasing the pressure and speed of the wind. Houses placed in narrow valleys will be naturally exposed to higher winds . It is critical to not omit this fact since the expected winds that will impact the house will be stronger than those expected in the area.
- Flood zones: Floods are a common consequence of high wind events such as tornadoes and hurricanes. A house placed in a flood-prone area won’t only need to be able to withstand the wind speed but should as well be elevated or placed higher on a slope to avoid this damage .
Estimating how much wind speed a house can withstand.
While it is impossible to give a straight answer to the general question of how much wind speed can a house withstand, it is viable to get a rough calculation with a specific house design, especially if it is engineered with that purpose in mind like the Deltec Houses. However, even if we can plan, design and engineer every small detail of the house to increase its resistance to strong winds, catastrophic natural events such as hurricanes and tornadoes can’t always be predicted as well as we would like to. Our constructions are every time more resistant, however unpredictable and unexpectedly strong winds can cause secondary events such as landslides, floods or the impact of flying debris, and even a building with a strong wind resistance can get seriously damaged.
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