Roof loss in tornadoes and the 60 cent solution

0 July 16, 2014 at 2:48 pm by

The EF2 tornado that tore through Angus, Ontario June 17 damaged 102 recently built homes in the small community located just west of Barrie. Ten or 11 homes lost their roofs entirely. These homes will have to be razed and re-built, at substantial cost to insurers and with significant disruption to the lives of the homeowners.

This home in Angus, Ontario was severely damaged after being struck by the roof of another house.

This home in Angus, Ontario was severely damaged after being struck by the roof of another house.

A few of the roofs became missiles, hitting other homes, causing damage that might not otherwise have been caused had it not been for the wind-borne debris. This was also a significant problem in Vaughan, Ontario, a fairly dense suburban community located north of Toronto, after two F2s tore through Woodbridge and Maple in August 2009.

Indeed, debris strike causes roughly half of all damage and many of the deaths and injuries incurred during severe wind events.

There is a perception among some that the problem with current home construction practices in Canada is that builders no longer double brick homes, as was done in the 1950s, and doing so might prevent much of the kind of damage seen in places like Woodbridge, Maple and Angus. However, whether a home’s walls are clad with brick, siding or something else, is largely moot  (though early research being conducted at such places as Western University in London, Ontario has found that there might be some merit in using brick over other types of veneers to guard against tornado damage to homes). Rather, the answer to building homes that are better able to hold up against weaker (EF0 to EF2) tornadoes and other types of severe wind events lies with roof connections.

The garage roof from this relatively newer home in Woodbridge or Maple, Ontario was lost in one of two F2 tornadoes that tore through Vaughan on August 20, 2009. Where did the roof go? It stuck the neighbour’s home, doing extensive damage.

The garage roof from this relatively newer home in Woodbridge or Maple, Ontario was lost in one of two F2 tornadoes that tore through Vaughan on August 20, 2009. Where did the roof go? It stuck the neighbour’s home, doing extensive damage.

In essence, if you keep the roof on, you will stand a better chance of keeping the walls up. The flipside is if you lose the roof, you stand a better chance of losing the walls. Roof loss increases the chance that walls will collapse on people, injuring or killing them, allows large debris to enter the wind field causing more damage downstream (as well and deaths and injuries), and opens the home to water ingress.

The problem with homebuilding practices in Canada is that we essentially build homes so the walls keep the roof up. We don’t really consider uplift forces created by severe wind events and the propensity of these forces to suck a roof upward. We, therefore, need to build homes to keep roofs down. This involves doing something other than the typical building code practice of sinking three toenails through each truss into the top plate of the wall.

Lab and field research being conducted at Western by Dr. Gregory Kopp (@GregoryAlanKopp) and his team of wind engineers has found that a few low-cost measures can protect homes from the most common wind-related damage. These include use of hurricane straps (aka hurricane clips or hurricane ties) – inexpensive metal fittings that connect trusses to walls.

Hurricane straps are somewhat difficult to retrofit into an existing home, but are very simple to put in during initial construction. What’s more, they are very low cost, particularly when compared to their benefit. Depending on the strap chosen, prices can range from around 60 cents apiece to about $2 apiece. With the average home requiring about 50 to 70 straps and one labourer about two hours to install – the total cost can come in below $150 for a home (including clips, screws and labour). The two hour installation time can be reduced as the labourer becomes more familiar with the task.

Now, ask the 10 homeowners in Angus who lost a roof – or their insurer – if they would gladly pay $150 now to have their home back the way it was before the tornado. They most certainly would say yes.

So the good news is that the fix to the roof uplift problem is simple and inexpensive.

The bad news is that it is very unlikely that homebuilders would opt to install hurricane straps without being told they must. So, the only way to get hurricane straps into new homes is by changing the building code.

ICLR is working to that end. In the past year or two, we have submitted several proposals to the National Building Code of Canada. However a big challenge has been to collect data on water and wind-related losses in order to be able to backup these code submissions. While there are some sources of storm loss and claims data that are available, the data are often too broad and lack granularity. We are taking several steps to get beyond these challenges so we can gather the proper data and photographic evidence so our code submissions will be successful.

In the meantime, insurers paying to replace a roof (or an entire home) damaged or destroyed from a wind event should require that hurricane straps be used in the new roof.

It would be very little money very well spent.



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