Nuts & olts”
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"Nuts & Bolts” How fast can wind destroy a home? Simple construction tips to keep yours standing The 23 rd Advanced Severe Weather Seminar March 15, 2014
Transcript of Nuts & olts”
"Nuts & Bolts” How fast can wind destroy a home?
Simple construction tips to keep yours standing
The 23rd Advanced Severe Weather Seminar March 15, 2014
Gone in Seconds
95 mph Straight Line Winds
EF-2 and EF-3 tornadoes with 111 mph-165 mph winds can destroy a property in four seconds.
Flying debris shatters windows and other openings and create holes in exterior walls.
Once an opening is created, air rushes inside the structure and pressurizes it like inflating a balloon.
The internal pressures build up and put pressure on ceilings and the roof, which is also getting uplift pressures from external wind forces.
If the connections between the roof and walls are weak, these wind forces will drive the roof and walls to give way. Once the roof blows off the entire structure can collapse within seconds.
1st Second
Flying debris shatters windows and pounds exterior walls. Winds blowing over the roof exert uplift, like an airplane. Roof shingles and pieces of the roof decking tear away,
2nd Second
Air rushes into the home through the busted windows, filling the structure with pressure like a balloon being inflated.
Internal pressure pushes up against the ceiling, joining the uplift on the roof from the gales outside in putting pressure on the roof.
The relatively weak connections between the roof and the walls give way and the roof blows off.
3rd Second
Roof is gone, walls are next. Unless there are a lot of interior walls bracing and going into them, the exterior walls are typically flimsy and not well attached to each other at the corners.
Though tornadoes spin in a cyclical motion, the fact that they're so big—with a typical footprint measuring 500 feet wide—means that a house is effectively hammered by straight-line winds. The side walls parallel to the direction of these winds will typically go first because they feel the most suction. The front, windward wall then gets pushed in by the tornado, and finally the back wall blows out, all within about a second.
4th Second
The last bits of a house that a tornado strike sweeps away are the interior walls Without exterior walls or a roof to brace them these inner walls can easily collapse or get blown over in the twister's fury.
This Applies to Commercial Structures
FORTIFIED homes need fewer repairs after disaster strikes.
FORTIFIED homes are better for the environment because they are not likely to end up as debris in landfills following disasters.
FORTIFIED homes may also be eligible for financial benefits such lower insurance rates.
FORTIFIED Home™ is a national, third-party verification program designed by the Insurance Institute for Business & Home Safety (IBHS) to help you assess the condition of your home, and then strengthen your home through an evaluation, inspection, and retrofitting process that is tailored to meet the challenges of specific, regional natural hazards.
FORTIFIED Home™ has three levels. Bronze, Silver and Gold, with Gold representing the highest level of achievement and the greatest disaster protection.
Something to Consider When Replacing Roof
IBHS wants you to know for less than $1,000, you can strengthen the roof of an average 2,000-square-foot house when replacing the roof.
Re-nailing the roof deck with 8d ring shank nails for better attachment.
Sealing the roof deck to keep water out of the attic if the roof cover blows off.
The Roof Makes A Difference
"Homes are not designed to withstand tornadoes," says Timothy Marshall, principal engineer at Haag Engineering Co. and an expert on tornado damage.
Building codes in non-hurricane designated areas call for two 16-penny (3 1/2 inch) nails connecting roof trusses to exterior wall top plates. These connections are intended to gird homes against gusts up to 90 mph for 3 seconds at a height of 33 feet. But even an EF-1 tornado is capable of more punishment.
It’s All about Connecting
Spend Now or Pay Later
Widespread use of effective strapping would create houses that are significantly more resistant to all kinds of severe wind events.
Estimated additional 2% of Framing Cost
1st Manmade Hail Storm
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IBHS 90 Acre Test Facility
In Chester County South Carolina There are 105 fans, each 350 horsepower and 5 ft. 6 in tall. They draw equivalent of 9,000 individual homes and 30 megawatts of power.
Each fan can push 230,000 cubic feet of air per minute. This flow volume is 20 times the flow going over Niagara Falls.
The top speed of the wind generated in the test chamber is 130 mph. Later renovations to the facility could increase that speed to 175 mph.
The turntable that holds the houses has a 55 ft. diameter and a surface area of 2,375 square feet with 52 anchor points embedded for bolting down test buildings.
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For more Information on Fortified Homes www.disastersafety.org
