Of all the pre-engineered metal roof applications, I am often asked which is the best roof curb design. Everybody has heard horror stories about curb installation failures. Many of these have been experienced firsthand. While very few would intentionally purchase and install the wrong product, curbs are often provided by those that don’t fully understand the implications of their choice until it is too late.
Curbs that aren’t designed for pre-engineered roofs (i.e. curbs meant for conventional roofs, knock down curbs), curbs not fitting the roof panel profile, and improper installation are some of the most common problems that I see. These items will help you choose the best prefabricated roof curbs for your customers.
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You should check to see if the manufacturer of your building has a preferred curb design. Some are very specific and may even require a certain type of curb to satisfy their warranty requirements. It is a smart idea to use their engineering knowledge if it is available. You may be able to avoid the pitfalls that they have discovered through builder feedback or trial and error.
Consider his preference if your erector is familiar with a certain type of curb. It can be difficult for him to install curb designs he doesn’t like or is not familiar with.
Roof Panel Type
Roof panels are available in four basic styles; trapezoidal standing seam, vertical leg standing seam, screwdown (‘R’ panel) and architectural standing seam. While one curb design may work perfectly on a given panel type, it may be totally inappropriate for another.
Roof Curb Type
There are many variations in curb installation methods, but there are three basic design categories.
• Uphill base flanges install under roof, downhill base flanges install over roof.
• Uphill and downhill base flanges install over roof.
• Uphill and downhill base flanges install under roof.
While each curb design has its advantages, not all curb designs are the best for every aspect of curb installation. A curb design that is simple to install might not have the best natural water-shedding ability. A more weather-resistant design might be required to be installed before the roof system is installed.