Canadian insurers have successfully lobbied a change to the Ontario Building Code regarding roofing on new homes, after research suggested damage following several Ontario tornadoes could have been minimized by some small changes.
The Institute for Catastrophic Loss Reduction (ICLR) team at London, Ont.-based Western University, along with letters of support from the Insurance Bureau of Canada (IBC) and several insurers, submitted proposals for three changes to the building code, of which one was accepted.
The change has been added to section 18.104.22.168 of the code and increases the number of nails in plywood roof sheathing on new homes from a 6x12 (inches) pattern to a 6x6 (inches) pattern.
“The 6x12 pattern requires that nails along the outer edge of a roof sheathing panel, where the panel shares the upper cord of the joist with the adjoining sheet, be spaced every six inches apart, while those nails in the interior of the panel can be 12 inches apart,” ICLR explained in a statement.
“A 6x6 pattern requires that nails be spaced six inches apart, regardless of whether they are on the outer edge or in the interior of the sheet,” which ILCR said is a much safer option in cases of extreme winds, and one that adds little to construction costs.
The submission was partially sparked by research following August 20, 2009, when 19 tornadoes occurred in Ontario, causing significant damage to roof sheathing, the ICLR noted.
At that time, “ICLR/Western researchers found instances of 4x8 plywood sheathing missing from otherwise relatively undamaged roofs,” the organization said.
The organization also saw similar damage in previous years after tornados in Ontario and after hurricanes in Florida and the U.S. Gulf Coast in 2004 and 2005, it noted.
“When a roof becomes depressurized in extreme wind, a poorly anchored roof panel may lift from the joists and become debris in the airstream, damaging other structures and/or vehicles and potentially injuring people or worse,” ILCR explained. “Missing roof sheathing also opens the home up to damage from water ingress, including growth of mould if the house is not properly dried out or repaired following a storm.”
ICLR says that this year, work is also underway on five proposals that will be made to the National Building Code of Canada.