Protecting Your Property From Wind Damage

by

Willy G. Henderson

SMASHWORDS EDITION

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PUBLISHED BY

Willy G. Henderson on Smashwords

Protecting Your Property From Wind Damage

Copyright © 2010 by Willy G. Henderson

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Protecting Your Property From Wind Damage

In 1954 a category 4 hurricane that was expected to dissipate, re-intensified and with winds reaching 110 km/hour dumped twelve inches of rain in 48 hours. On the dawn of the third day, 81 people were dead and 4000 families were homeless. If this sounds like Haiti, well you are right, at least partially. The hurricane was born off the coast of Africa, picked up speed crossing the Atlantic and vaulted over Haiti killing an estimated 1000 people. Incredibly, most of the people drowned as water rushed down mountain peaks as high as 2400 meters. Although the mountains robbed the mass of much of it’s energy, it gathered force as it crossed the Caribbean making landfall in the Carolina’s. It cut a swath of death and destruction across 1100 km of land through Delaware, Maryland, the Virginia’s, New Jersey and New York until cooler air finally slowed its advance and it stalled out over Southern Ontario.

When Hurricane Hazel struck in October of 1954 my mother was a teenager living in Willowdale just to the north of the washed out Lawrence Avenue Bridge and tragic Raymore Drive. Over 30 houses were washed into the Humber River along with 35 of the 81 Ontario fatalities of the storm. I remember my family and especially my grandparents talking about Hazel many times. They were so surprised, shocked even, that a hurricane could reach their city so far away from the tropics. Now I can honestly say I know how they feel. As unthinkable as Hurricane Hazel was to them then, tornadoes are as incredible to me now. When I was a kid, tornadoes only happened in Kansas.

Ontario is the meeting place of two air masses: the dry air from the prairies and northwest and the hot humid air from the American south and southwest. As summer progresses fantastic thunderstorms erupt along the leading edge or fronts of these colliding masses. Anytime warm, moist air near the ground rises to meet the colder air above the greater the chances of quickly forming, fast moving thunderstorms. Such was the case on July 14, 1997 in mid afternoon when Environment Canada’s radar indicated no rain at all while 20 minutes later, a severe thunderstorm formed near Punkeydoodles Corners; between Kitchener and Stratford. In the span of a few hours 20 cm of rain fell in winds clocked at 115 km/hour, uprooting trees and downing power lines. If the right conditions exist such as a deep low-pressure area and a strong cold front, a line of thunderstorms will be created. Such was the case on May 31, 1985 when 11 tornadoes hopped across Southern Ontario, killing 12 people and causing more than $150 million in damage.

Whether you believe humanity is responsible for erratic weather patterns or you just think our forebears lived in a more climatically stable time, as Bob Dylan says, “For the times they are a-changin’”. The Insurance Bureau of Canada maintains that weather related claims have doubled every 5 to 10 years since 1950. While a hurricane like Hazel happened over 50 years ago, it appears that the frequency of storms accompanied by high winds are occurring with greater frequency. Tornadoes have moved from the realm of fantasy up the yellow brick road to reality as each summer brings confirmed reports from populated areas such as Vaughn and Fergus. The best we can do in light of our changing weather conditions is be prepared for the wind when it comes.

Assessing Building Vulnerability to Wind Damage

There are basically three main areas of concern when assessing the ability of a building to resist wind damage. Ideally, the surrounding topography of a building site should be considered for some natural shelter from the wind. The smoother the terrain, the greater the wind load. If you had the choice of where to build, it is worth noting that thunderstorms increase in intensity as they increase in elevation and decrease in intensity as they travel down the slope. It’s almost as though all of that energy collects as a giant rolling spring pushed against the sky only to relax on the other side of the slope as it carries on. Unfortunately, most of us have limited control over the site surrounding our homes and businesses.

Next to consider is the skin or building envelope of the dwelling; that part of the building that keeps the elements out and the warm, dry air in. Windows, doors, siding, and the roof all act as the skin of the building. The building envelope must be water shedding and as airtight as possible. Since water usually accompanies high winds any breach in the skin of the building will likely be followed by water damage. It takes little imagination to realize how much damage one lost panel of roof sheathing or one smashed window in a torrential thunderstorm could cause.

One last area to consider when assessing a building likelihood to resist wind damage is structural integrity. Wood framed one and two story homes, as well as manufactured homes are lighter and more susceptible to wind damage if precautions are not taken during construction. Measures can be taken to strengthen the structural integrity of these lighter buildings after construction but such measures are both costly and intrusive, often requiring the occupants to leave for a time to during retrofit.

Survey Lot for Potential Problems

Protecting the building envelope from wind damage begins with a site inspection. Be aware of objects that can become lethal airborne projectiles in high winds, such as:

• lawn furniture

• garbage cans

• turn off propane tanks

• store barbecues

• potted plants

• garden sheds should be anchored

• bikes, boats, canoes

• lawn mowers

• toys

Store away any objects that can be easily picked up by high winds and thrown through a window or door. Any items that are too large and cumbersome to be stored should be bolted or chained to decks and concrete slabs. If there is no permanent decking or foundation to attach these items then use straps and ground anchors such as those used for mobile homes.

In many cases tree damage due to wind is avoidable. Properly pruned and disease free trees cannot damage your house. Pick trees that are indigenous to your area and therefore better suited to the wind and soil conditions. Plant trees far enough away from any buildings so that if they do fall they will not cause damage or injury. Compact soil, circling roots, decay, pests, disease and structural issues caused by improper pruning are all serious concerns for large trees on your property. Inspection of large trees will reveal splits in the main trunk that can be bolted and limbs that could be cabled together to prevent further damage providing years of continued enjoyment.

Trees need to be aggressively pruned to keep the trunks thick, the root system reaching and overall height restricted.

Importance of the Building Envelope

High winds striking an exterior wall exerts a positive pressure on the wall, thereby forcing air into the building through any openings, somewhat akin to blowing up a balloon. As the windward wall is receiving positive pressure, the rear and side walls are receiving negative pressure or suction as the air is being pulled out through the openings in these walls by the passing storm winds. Poorly sealed windows and doors due to the porosity of the building envelope cause such internal pressure changes. Therefore, if the porosity of the windward wall is greater than the combined porosity of the other walls, there will be positive pressure. When there is positive pressure within the building, roof uplift will occur. Alternatively, if the porosity of the windward wall is less than the net porosity of the other walls, there will be negative pressure. Internal negative pressure will create depressurization and suction on the roof.

Lowering the overall porosity of the building envelope doesn’t mean that you have to have a home that is airtight all of the time. Everyone wants a healthy environment in which to live and work. However, protection of the building requires that when the strong winds are imminent, action can be taken to decrease the building porosity on short notice. An inspection of the building envelope should be done once each year to ensure building porosity is optimal:

• inspect roof sheathing from inside the attic and make sure the panels are nailed securely to trusses or rafters; if you find nails that have missed their mark, obtain small L brackets from the hardware store and screw the panels to the trusses or rafters taking care to use short screws on the sheathing so as not to puncture the sheathing entirely

• gable end roofs should be braced in an X fashion with two 2x4’s extending four trusses/rafters back to the peak/floor of the gable

• gable roof vents should be shuttered securely to the vent frame to prevent water intrusion

• make sure all roof drains and gutters are clear

• check for leaks around windows and doors ensuring weather stripping has not failed

• peeling paint is often a sign of moisture in the wood, make sure all exterior walls are well sealed and painted

• look for discolorization of paint and caulking, swelling of window and door frames

• inspect all flashing around doors, windows, thresholds, chimneys, where two angles meet, and so on

• roof vents, exhaust vents and so on should be flashed properly to prevent leaks and anchored to the roof

• use a good quality silicone caulking to seal around anything that extends through the skin of the building, such as electrical outlets and bathroom vents; it is a good idea before a storm to close off the bathroom vents with duct tape but don’t forget to remove after the and don’t use the vent until the tape is removed

• if you live in an area where you think shutters are a good idea then be sure to attach them to the window frame in which the glazing sits; if not properly installed these shutters can become projectiles in high winds

• metal and solid wood doors can withstand some heavy impacts but hollow core, glass and French (double entry) doors may require shuttering

• all doors should have three hinges and a dead bolt with one inch throw length

• French doors should have barrel bolt pins that extend through the door header and through the threshold into the sub-floor

• Retrofit packages for single and double garage doors are available to reinforce doors in strong winds

This list is not all-inclusive and only encompasses some of the most obvious potential weaknesses to the building envelope from wind damage. An experienced restoration expert is the best person to do a full audit on the readiness of a building to withstand the stresses of high winds.

American Standard Test Method (ASTM) D 4756 claims that a new standard for PVC siding that provides

for more nails and a deeper J channel in the siding will prevent scenes like this one in Toronto last summer.

Structural Issues Best Addressed during Construction

The primary concept to understand when dealing with a buildings structural ability to withstand strong winds is that of providing a continuous load path or a chain from the roof to the foundation. Starting from the top, the roof sheathing is fastened to the roof framing, the roof framing is connected to the top plate, the top plate is connected to the wall stud, the wall stud is connected to the bottom plate and the bottom plate is bolted to the foundation. Every place there is a joint is connected by a metal strap or plate. For added security in areas where extreme winds are seasonally prevalent, metal hurricane strapping is recommended to attach trusses/rafters over top plates to fasten onto wall studs.

Building innovations to improve continuous load throughout the structure is great during the construction of a building. However, older buildings would require extensive and costly renovation to benefit from this relatively new concept. So it boils down to a balance of continuous load path upgrades that are structurally non-intrusive and diligent building envelope porosity maintenance that will bring the most security to building owners and insurers.

Flat Roofs Can Be Costly

Over the years loose laid membranes on flat roofs have become common. One of the biggest problems with this method is the gravel blow off and scour that is endemic of this type of roofing. The problem with gravel blow off is obvious for neighbour’s windows, automobiles and personal safety. Increasing the aerodynamics of the roof edge, the height of the parapet and the stone size of the aggregate can rectify these problems. However, if scouring occurs leaving areas of the roof uncovered then UV, weather and foot traffic may cause the membrane to fail and the roof to leak.

When insuring or reviewing claims involving flat roof loose laid membranes it is important to be aware of proper maintenance practices required of these installations. If strong winds rip off exposed and improperly installed HVAC ductwork, air conditioning condensers or satellite dishes weighed down with cinder blocks, who is liable? The policyholder should keep regular inspection and maintenance records of the roof and equipment. And a visual inspection of how the equipment was secured to the roof should be completed when presented with an insurance claim.

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NOTE TO THE READER

This is an article that appeared in the June 2010 issue of the Ontario Insurance Adjusters Association's magazine 'Without Prejudice' under the title "The Times They Are A-Changin'" on page 16.

In addition to working as a Project Manager for construction and disaster restoration companies, Willy G. Henderson has Textile Engineering, Business and Economics degrees and is technically competent to write on many subjects. Those interested in having articles written should contact Willy at this address:

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