Metal roofs made of galvalume plated steel provide great corrosion resistance and can easily meet the warranty of 20 years. However, when large penetration on the roof is needed, such as a large fan or other equipment, the integrity of the roof can be compromised if it is not handled correctly.
The general method to deal with large penetration is installing the mechanical roof curb that forms the transition between the roof and equipment installed. Of course, like most aspects of building construction, there are choices available in materials, methods, techniques, and styles of installing a roof curb. When the key objective is to provide a curb that will perform for the entire life of the standing seam roof, there are some key points to keep in mind.
Choose the right material:
A galvalume-coated roof doesn’t mean that a galvanized steel roof curb is the best thing to use – in fact, galvanized roof curbs are known to rust, corrode, and leak, particularly along weld joints, as soon as a year after installation. Instead, a curb made from aluminium (preferred) or stainless steel should be used to prevent premature corrosion.
Use the right type of roof sidewalk:
It is not uncommon for a roofer to choose a curb type referred to an “over/over” curb, meaning that, after the opening is cut, the curb is installed over the roofing on both the upslope and the downslope sides. This might be the easiest to install during construction, but it will very likely create more work and callbacks when the upslope side starts to get water into or under the joint, and leaks. Instead, it is well worth taking a few extra minutes to install an “under/over” curb, which places the upslope side under the roofing in a true shingled lap between the curb and the roof.