Galvalume sheet has been successfully used in roofing applications for more than 25 years (see Advantage Roofing); it has been evaluated in outdoor tests for well over 30 years, based on these tests, in which corrosion weight losses were measured and compared with galvanized, Galvalume sheet is expected to outlast galvanized sheet (with an equivalent coating thickness) in various atmospheres by up to 9 times.
Regarding warranties customer needs to consider the two types of Galvalume roofing system that are used, structural and architectural systems, structural systems are those that are installed directly on the roof structural system (i.e., purlins) without decking, these are low slope systems, up to about 1:12 pitch, using bare, heavier gauge Galvalume steel sheet, use in this application Galvalume is guaranteed for 20 years. Architectural Galvalume roofing system are those used in applications in which the roof is being used not only for protection against the weather but also for its appearance, because architectural roofing system are used as a design feature of the building, such systems are used at high slopes, usually up to 4:12, for both residential and commercial buildings. In most cases the Galvalume panels are prepainted in a wide range of colours using today's high performance paint systems.
Warranties cover both the Galvalume sheet and the paint system; most Galvalume roof suppliers give the same warranty for the Galvalume steel substrate for prepainted roofing as that for bare roofing, many supplies also give a 5 year warrantee against chalk, fade and peel of the paint system, beyond the 20 year Galvalume roof warranty, depending upon the paint system and environmental conditions.
Wooden decking is normally used for prepainted Galvalume architectural roof systems on both residential and commercial applications, but it is not recommended to install the panels in direct contact with the decking, instead a 30 pound felt or an equivalent should first be installed on the decking and the roof panels before installation over the felt. For new residential construction applications, the roof panels would be installed over roofing felt on wood decking.
Galvalume sheet can be expected to provide long life, flashing should be used that will last a life that commensurate with Galvalume sheeting, for bare sheet roofing, Galvalume sheet flashing is preferred, although aluminium flashing is also acceptable, galvanized flashing is not recommended because it will not provide comparable corrosion resistance, for pre-painted sheet roofs, flashing as well as trim parts should preferably be made from pre-painted Galvalume sheet from the same colour and coil line batch for both initial colour matching and long term colour change during weathering.
There are a number of variations of concealed fastener systems, for low slope structural systems, panels are overlapped and lockformed or snapped together at the seams and held down with clips, one end of which is overlapped in the seam and the other end fastened to the structural member of the roof. The clips have a sliding feature that permits the roof panels to "float" during expansion and contraction from environmental temperature changes.
From a practical standpoint, the life of a pre-painted Galvalume panel is dictated by the performance of the paint appearance as affected by conditions of fade, chalk and peel and the life of the paint is determined by the type of paint system and the weathering conditions to which it is exposed. Almost all home owners will repaint a pre-painted roof or sidewall when the appearance of the colour is determined to be aesthetically unattractive from weathering.
Paint systems applied on modern coil coating lines can be expected to provide good to excellent performance in nearly every environment. The most commonly used topcoats are acrylics, polyesters, siliconized polyesters and fluoropolymers, when combined with chemical pre-treatment and high-performance primers, these topcoats enhance adhesion to the metal coating and increase overall corrosion resistance, particularly at cut edges, scratches and bends.
The best way to buy Galvalume roofing system is through the roof manufacturer/ suppliers, they have qualified and affiliated contractors who are trained and approved to install their roof systems, it's important that only experienced and approved contractors be used to install Galvalume roofing systems.