Purlin

Purlins run horizontally across the slope of the roof, perpendicular to the rafters or trusses, and provide the direct fixing points for metal roof sheets. On a metal roof, the roof screws pass through the sheeting and into the purlins, which transfer the load to the trusses or rafters below. Purlins can be timber (typically 70x35mm or 90x35mm treated pine) or steel (light-gauge C or Z-section purlins), with the choice depending on the building type and span requirements. Timber purlins are standard on residential construction in Australia, while steel purlins are more common on commercial, industrial, and agricultural buildings where longer spans between structural supports are required. The spacing of purlins is determined by the wind-load zone and the spanning capacity of the roof sheeting profile — in general areas, purlins may be spaced at 900mm to 1200mm, while in high-wind zones at the edges and corners, the spacing is reduced to as little as 600mm. In Gippsland, purlin condition is assessed during every roof replacement. On older homes with galvanised iron roofs, the timber purlins may have deteriorated due to decades of exposure to moisture leaking through corroded roofing. Town & Country Roofing replaces any damaged purlins as part of the roof replacement process, ensuring the new roof covering is fixed to a sound substrate.