Guide on How to Install a Roof Curb on a Metal Roof
Metal roofs made of galvalume plated steel provides 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 properly.
The general method that deals with large penetration (i.e., stretches more than one or more standing stitches) is installing mechanical roof curb that forms the transition between the roof and equipment installed. Of course, like most aspects of building construction, there are options available in materials, methods, techniques, and style of installing roof curbs.
When the key objective is to provide a curb that will perform for the entire life of the standing seam roof, there are two key points to keep in mind.
Image Source: Google
Choose the right material:
Galvalume layered roof does not mean that the galvanized steel roof sidewalk is the best thing to use – in fact, galvanized roof sidewalks are known to be rusty, corrosive, and leaking, particularly along weld joints, as soon as a year after installation.
Conversely, the sidewalk made of aluminum (preferred) or stainless steel must be used to prevent premature corrosion. To put any concerns about dissimilar materials and galvanic corrosion to rest, keep in mind that galvalume is approximately 80 percent aluminum by volume, so they are highly compatible.
Use the Proper Roof Curb Type:
It is not uncommon for a roofer to choose a curb type referred to as 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. This way, the upslope edge is much more protected and less likely to leak using the same shingled condition occurring on the downslope side – all creating a properly water-shedding, weathertight condition.