Thermal Expansion

All building materials change dimension with temperature, but metals are particularly responsive. A 6-metre Colorbond roof sheet can expand by approximately 5mm between a cool morning and a hot afternoon, and this movement occurs daily throughout the life of the roof. The coefficient of linear expansion for steel is approximately 12 x 10^-6 per degree Celsius, meaning a 10-metre sheet will grow or shrink by roughly 0.12mm for every degree of temperature change. The effects of thermal expansion on roofing include: "oil-canning" — visible rippling or waviness in flat areas of metal sheets; "ticking" or "popping" noises as sheets move against fixings and each other; screw hole elongation where sheets have been fixed too rigidly; and lifting or displacement of improperly restrained flashings. These effects are most pronounced on dark-coloured roofs (which absorb more solar radiation) and on long, unbroken sheet runs. In Gippsland, thermal expansion is a significant design consideration due to the wide temperature range experienced between seasons and between day and night. Dark Colorbond colours such as Monument, Woodland Grey, and Night Sky are popular choices but absorb more heat and experience greater thermal movement than lighter colours. Town & Country Roofing uses correct fixing techniques — including slotted brackets and a combination of fixed and sliding fasteners — to accommodate thermal movement on every metal roof installation.