Failures on re-roofed houses

By David Henderson, Korah Parackal, John Ginger and Daniel Smith.

Recent severe weather in Tasmania downed trees, power lines and caused the failure of some house roofs. One of these roof failures, seen in a photograph on ABC online, shows the removal of a large section of roof cladding due to the failure of batten to rafter connections.

The close spacing of battens points to the house originally having a tile roof that has been re-roofed with corrugated cladding.  It looks like this newer metal sheeting had been screwed to approximately every fifth existing batten and these were removed entirely by the wind, along with the cladding. A large number of similar failures were seen during the Brisbane thunderstorms of November 2014 at wind speeds below design level by the Cyclone Testing Station team.

Builders and homeowners need to take into account the entire 'hold down chain' when conducting renovations and repairs, especially when replacing tile roofs with metal sheeting, as the batten to rafter connections will be subjected to much larger uplift loads since the metal cladding is lighter than the tiles.

Research at the Cyclone Testing Station, and supported by the Bushfire and Natural Hazards CRC, on 50-year-old old batten to rafter connections from Adelaide has shown that their strength can decrease by more than 50 percent due to the drying out of timbers and degradation of the nails. These connections must be upgraded when replacing roof cladding on older homes.

The Cyclone Testing Station webinar series for homeowners and builders provides essential information on upgrading roofs, including replacing tiles with cladding.