Damage to Residential Construction from the Tornadoes in Vaughan, Ontario, on August 20, 2009

The results of a detailed damage investigation of the two tornadoes in Vaughan, Ontario, which were part of the 19 tornadoes in the outbreak of August 20, 2009, are presented. The bulk of the damage in both tornadoes consisted of structural roof failures categorized as F1 on the Fujita Scale and EF1 on the Enhanced Fujita Scale. However, multiple houses in both tornadoes suffered total roof failure, which is F2 (or EF2). It was observed that the total roof failures were all due to either internal pressurization and or weak (or non-existent) roof-to-wall connections. Since internal pressures are likely to be larger than external pressures for these single family residences, it is argued that the total roof failure occurred under wind speed conditions associated with a lower degree of damage, such that actual wind speeds are like those in EF1 in these particular tornadoes.