In severe windstorms sheet metal roofs can become deadly missiles even in areas of Australia not affected by cyclones. This is because the wind uplift forces are greater than the weight of the roof and the “tie-down” fixings are, in some cases, not strong enough to resist the uplift effect.
To overcome this problem, Pryda has developed a range of framing tie-down connectors to suit all requirements in buildings. Tie-downs have been required in buildings for many years. To help designers and builders select and install connections of adequate strength, the 1999 version of AS1684 introduced tables of uplift forces and tie-down connection capacities. Selection is based on the roof load width, connector spacing and wind classification for the site. Building inspectors and surveyors are now enforcing these requirements, which stipulate that tie-downs must be part of the structural system of a timber frame.
It is important, therefore, that specifiers specify connectors with appropriate tie-downs when quoting on any project. To help builders comply with these new rules, Pryda has released its Connectors and Tie-downs guide with connector selection tables. The guide also gives details for the installation of these connectors including nails and fixings required.
Presently, many building drawings lack specifications for tie-downs but this will now need to be addressed by both designers and builders to comply with AS1684.
Source: Building Products News.