What do you know about wind-resistant buildings?

Each year, Wisconsin normally experiences 23 tornadoes, based on the years of 1981-2010, and well over 1000 tornadoes occur each year in the United States.  Consequently, each year a number of residential homes, businesses, and agricultural buildings are severely damages or destroyed; and a number of people are injured or killed by tornadoes.  So this begs the question - is there such a thing as a tornado-resistant building? 

Current building practices and technology do allow one to construct a more tornado-resistant, or wind-resistant building.  This would also apply to severe thunderstorm straight-line wind situations, since powerful winds of hurricane-force can also result in considerable damage.

How can I make my home more wind resistant?

Building codes dictate that homes built today have some minimum anchoring with bolted-down sill plates, toe-nailing of floor joists, straps, and perhaps some kind of hurricane clip for the roof trusses. Keep in mind that building codes vary from county-to-county and state-to-state, consequently the wind-resistant capabilities of buildings will vary.  However, you can construct or retro-fit a building with a variety of additional metal braces, brackets, clips, straps, cables, hooks, and bolts/nuts/washers, such that that building becomes stronger and better able to withstand powerful tornadic winds or severe thunderstorm downburst winds (microbursts).  In other words, you can make a structure more wind-resistant, but not tornado-proof.  Work with your building contractor to identify what extra re-enforcements, better known as "anchoring devices" are best for your structure.  Obviously there will be an extra cost involved.

Basically, in buildings constructed with wood, any location where wood meets wood is potentially a failure spot where a structure can come apart.  Nails are typically used to hold two different pieces of wood together in most interior and exterior walls - and can do only so much in holding wood together during a tornado or non-thunderstorm high-wind situation.  Additional anchoring devices installed at these potential failure locations will make that joint stronger and more resistant to damaging winds.

Typically, an attached garage is the first part of a residential home that fails since the garage becomes a "sail" once the wind penetrates the garage. Once the garage is ripped off, the inside of a home is exposed to penetrating winds which may pressurize and tear apart the remainder of the home.  Therefore, you may want to install additional anchoring devices on your garage walls.

Some homes are constructed with thick, concrete walls (above-grade exterior walls, usually only the first floor, are concrete in addition to the concrete basement walls).  This type of home will obviously withstand strong winds better than a stick-built home.  However, even concrete homes will sustain some degree of window, trim, and roof damage since these parts of a home will usually not be made up of concrete material.  Of course, it’s much cheaper to replace a window and trim and roof shingles than an entire exterior concrete wall.  Refer to additional references to concrete homes further down in this Top News Story.

Another point to remember is that airborne missiles in stronger tornadoes may be able to at least partially penetrate concrete walls, but it is unlikely that airborne missiles would be able to penetrate a 1-foot thick concrete wall.  Obviously, airborne missile penetration would be more difficult for a concrete home compared to a wood home.

Dome buildings, by nature, offer less wind-resistance.  Therefore, they are better able to withstand the power of tornado winds and straight-line, thunderstorm downburst winds, especially if they are constructed with steel and concrete.  There will still be some damage due to debris missiles, but pound-for-pound, there will be less damage as compared to a conventionally-built, stick home.   Earth-berm homes also offer less wind resistance since they are partly underground.  Some commercial companies also build wind-resistant windows that can withstand stronger winds as compared to "normal" windows.

Caution - even structures that have been re-enforced with additional anchoring devices (beyond local building code requirements) will sustain some damage in a tornado situation.  Potentially, the degree of damage will be less since that building is more resistant to strong winds.  Obviously, some degree of window, trim, and roof damage will still occur with all but the weakest of tornadoes; and the entire structure may yet fail in a violent tornado.  However, pound for pound, a building with a variety of additional anchoring devices will be more resistant to damaging tornado winds compared to a building with little or no extra anchoring devices beyond what is dictated by building codes. Nothing can protect a stick-built building from airborne debris and missile impact.  Below are some images of anchoring devices.

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MBK joist strap

What about basements - Am I safe in a basement?

Being in the basement of a building is better than being outside or in the floors above the ground level since you reduce the chances of being impacted by flying debris and missiles.  However, large pieces of debris, that can crush you, can be pushed into basements by powerful tornado winds.  So you need to get under a strong work bench or table that can support the weight of heavy debris, or perhaps you can go under the stairs leading down into the basement.  Cars, pick-up trucks, and other large pieces of debris can be pushed into basements - do you have a table or bench in the basement that can support the weight of a car or pick-up truck?  Note the large pieces of debris pushed into the basement shown in the picture below.

Luckily, most of Wisconsin's tornadoes are weak, and the sub-floor that covers a basement will usually remain intact during the passage of a weak tornado.  This means that in weather tornado situations large pieces of debris will usually not end up in a basement.  Consequently, getting into a basement is an excellent option in order to protect yourself.

Alternatively, some people build "safe rooms" in their basements - a 6’ x6’ or 8’ x 8’ concrete room with steel re-enforcements.  These rooms offer the best protection in a basement.  Some people install safe rooms underground in their backyard, or under the garage floor.  Those people who have a home with no basement can chose to have their safe-room located on the 1st floor of the house, with the safe-room doing double-duty as a den or extra bedroom.  Using a search engine on the web, do a search on "safe rooms" to find additional information.  FEMA provides additional information about safe rooms at this link:  http://www.pathnet.org/sp.asp?id=1625

Is a "concrete" home "tornado-proof"?

Some people choose to have commercial companies build them a concrete home, rather than a "stick-built" home.  The side walls of concrete homes are typically on the order of 8 to 12 inches in thickness.  Additionally, embedded steel bars or wiring will reinforce the strength of the concrete wall, and the insulating value of such walls is well documented.  Some manufacturers advertise their concrete homes being able to withstand winds up to 150 mph.  If this is true, then this kind of home can withstand an EF-3 tornado (EF-3 tornadoes have winds of 136-165 mph).  This implies that the concrete walls will sustain a significant amount of damage in an EF-4 or EF-5 tornado.  Obviously, windows, doors, and the roof structure of a concrete home will sustain significant damage in an EF-3 tornado due to the tornado winds or airborne debris/missiles.  However, the walls should sustain minimal damage.

The bottom line is - the greater the amount of concrete and steel in a building, or the more rounded the buildings, the more wind-resistant it becomes.

What do I do if I own a large business, or work for a large business?

Does your business have an emergency plan and do you practice it like a fire drill in a school?  Are there designated "safe-rooms?"  Do you have a NOAA Weather Radio All Hazards unit to receive the warning directly from the National Weather Service?  Does your business have designated "weather watchers" who are trained spotters and have access to on-line radar and warning information?

Does your business have a continuity/recovery plan?

The Racine County Emergency Management staff generates emergency preparedness articles on a monthly basis for the Racine County web site, and in the September, 2008 issue they provided information on business preparedness (see below):

Small businesses are vital to the economic health of a community, accounting for more than 99% of all companies and employing 50% of all private sector workers.  Unfortunately, many small and medium sized businesses don’t take the time to prepare in advance, often citing both time and money as major factors.  But at what expense?   Research indicates that at least 25% of small and medium sized businesses do not reopen after a disaster.

Every business should have an emergency response plan and a continuity/recovery plan.  The emergency response plan will outline the action steps that you and your staff will undertake to protect life, safety and property.  The continuity/recovery plan will aid in your recovery from an emergency/disaster and will ensure that your business continues to operate, even off site if necessary.

There are tools out there to assist businesses in developing these plans.  The Department of Homeland Security has a Ready Business website (www.ready.gov) and the Institute for Business and Home Safety has a fill-in-the-blank template available at www.disastersafety.org/business_protection.

 


 

Additional resources available on-line

Below are some web sites with additional preparedness information.  FEMA sites have a lot of planning information - so take advantage of it.  Unless you are constructing a home or business with very thick, solid, steel-re-enforced concrete walls and roofs (with no windows), nearly every structure built will sustain at least some degree of damage due to tornado impact.  Obviously, the stronger the tornado is and the slower it is moving, the greater the amount of damage.

http://www1.eere.energy.gov/buildings/disaster_recovery/dr_residential.html

http://www.fema.gov/rebuild/index.shtm

http://www.fema.gov/plan/prevent/property.shtm

http://standeyo.com/Reports/FEMA.Shelter.html

http://www.wvdhsem.gov/WV_Disaster_Library/Library/CONTACTS/Publications.htm

http://www.crh.noaa.gov/grb/?n=schools

http://www.crh.noaa.gov/images/grb/outreach/brochures/WeatherPlanningStrategy.pdf

http://www.depts.ttu.edu/weweb/shelters/windprotection.php

http://www.depts.ttu.edu/weweb/Shelters/Shelters.php

http://www.crh.noaa.gov/mkx/edu.php
http://www.fema.gov/plan/index.shtm
http://www.crh.noaa.gov/grb/?n=prep

Refer to an associated Top News of the Day story entitled "Homes, Businesses, Schools - How do you know if a tornado warning has been issued?"   Both stories will be archived in the Top News Archive on this web page -

http://www.crh.noaa.gov/news/display_cmsarchive.php?wfo=mkx

Using web-browser, type in the following phrases to find additional information on how to make structures more wind resistant: "hardware brackets" or "anchoring devices," "wind-resistant buildings, "dome homes," "wind-resistant windows," "wind-resistant doors."

Questions?  Contact me at Rusty.Kapela@noaa.gov



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