How to Choose the Right Style Roof Curb

How to Choose the Right Style Roof Curb

Tips for Choosing the Right Style Roof Curb for Your Metal Building

Roof curbs have become a common accessory for standing seam roofs. As a result, it’s critical that they also offer leak-free protection for 20 years, just like your roof.

For building designers and roofing contractors, it’s important that they make good decisions regarding the roof curbs they opt for.

Here’s what you should consider before deciding on the right roof curb.

What to Keep in Mind About Roof Curbs

Roofers typically prefer to use an over/over type curb. This requires the curb to go over the panel on both upslope and downslope ends.

At the upslope end of the curb, the joint between the panels and the curb is lapped backwards against water flow. This leaves the area un-shingled and most refer to this area as a “backwater lap.”

However, this curb tends to lead to leaks. You can get a seal across the panel until you hit the seam. That’s why we recommend an under/over curb. This curb is lapped under the roof panels at the upslope end and over the roof panels at the downslope end.

Side Flanges vs. Rib-to-Rib

The vast majority of curbs have 4- to 6-inch-wide side flanges. This style demands that the curb transition from being under the roof at the upslope end to over the roof on that downslope. Roofers, as a result, tend to cut a slit in the roof panel on each side, so the transition is easier. But this leads to an unsealed spot.

Alternatively, a rib-to-rib curb offers sides that cover the next panel rib. This allows for a curb to seal to the roof on both sides, pushing water away rather than into the flat of the panel. Not to mention, this choice is easier for roofers to install during the roof installation process.

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