Roof Curbs for Metal Roofs

Dec 19, 2017 3:37:59 PM / by Clint Funderburk

Are all roof curbs for metal roofs are the same?

FALSE. There are several differences in a typical roof curb for metal roofs that need to be addressed to insure that you are specifying the correct product for your next projects.  There is a standard roof curb spec that is inteded for TPO / built up flat roof application & is not written for pitched metal roofs. This spec has been inserted into specifications for years that causes many problems down stream – from the bidding process all the way to the installation.  Keep in mind the end user and the importance of providing a weather tightness roof.

When designing a building, most attention is placed on the overall function, structural requirements, and the overall visible appearance of the building.  Once past the design stage, then all of the products to be used need addressed.  However, the less exciting products (ex. Roof curbs, Skylights, A/C units) can be extremely critical in the outcome of a successful project.

When evaluating roof curbs, first the material used must be aluminum - NOT galvanized steel, Aluminized or Galvalume. Why? Aluminum has a incredibly long life span, has lasting strength, and is extremely stable through the ranging temperatures of heat and cold.  Most importantly, aluminum will not rust. Galvanized Steel, Aluminized Steel and Galvalume materials when cut or welded will rust, which decreases the life span of the roof curb and possibly the metal roof.  Rust from the roof curb will run onto the metal roofing causing an unsightly look as well as damage the panels.

A roof curb must be designed for an under/over installation and with the curb base sides extending to the next natural seam with integral highs. Why? This design creates a natural shingle effect and allows the roof curb to become an integral part of the roof system; therefore, eliminating leaks when a roof curb is installed as an over/over or under/under flat base style curb.  Over/over and under/under installations are completely reliant on caulk, tapes, and screws which will result in a leaking roof.

A roof curb must have an integral cricket on the upslope side to deflect water around the sides of the roof curb.  The integral cricket also eliminates water from ponding on the up slope side.  Another overlooked detail is correctly supporting the roof curb.  Roof curbs must be supported with a floating sub frame package that is to support the roof curb from sagging, which in turn, applies stress to the roof curb, the metal roof, the screws, and sealants.  Once sagging occurs, it is not long before you have water ponding and then roof leaks are inevitable.

Lastly, roof curbs should be specified with a standard 20 year warranty that matches the 20 year warranty of the metal roof panels. Why?  Roof curbs and metal roofs go hand in hand. 

Metal Roof Curb for Standing Seam Metal Roofs and Exposed Fastener metal roofs

With LMCurbs being involved in the metal building industry for over 40 years, we have seen our share of the end users receiving the wrong roof curbs. As a result of these wrong curbs, customers ended up with roof leaks that are being patched over and chasing the leak locations. During which time damage has occurred to the interior of the buildings,  Product / Inventory damage & loss, production loss, loss of electrical equipment. 

Where do we go from here?

First, architects and specifiers should specify the correct roof curbs that meet or exceed the following:

  • 0.80" or .125" Aluminum construction
  • Under / Over design
  • Curb base flanges must match the roof configuration of the roof panel
  • Integral cricket
  • Floating sub frame package
  • 20 Year Warranty

 For more Aluminum Roof Curb information


Topics: Roof Curbs, Metal Roof Curbs, Metal Roof, Standing Seam Metal Roofs, Exposed Fastener metal roofs, 20 Year Warranty

Clint Funderburk

Written by Clint Funderburk