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Selection and Installation of Curbs on Hydrostatic Low-Slope Coated Steel and Aluminum Roofing

This document describes best practices for the selection and installation of curbs used specifically on low slope (less than 2:12), coated-steel or aluminum roof systems. Steep slope or architectural roofing is not addressed in this document. Different design considerations for curbs are required for steep slope roofing and for materials other than coated steel or aluminum.

There are several factors an installer should consider in order to provide the best possible curb installation. The following are suggestions for a weather-tight and long lasting curb installation: An installer should: 

• Use curbs made from .080” aluminum or 18 gauge stainless steel. Galvanized and Galvalume® curbs do not offer the long-term performance of aluminum or stainless due to the vulnerability of the welds. 

• Use curb details as recommended by the roofing manufacturer. Failure to do so could void manufacturer’s weather-tightness warranties. 


• Use “over/under” shingled curb configuration 

• Use the following clearances: 

o Minimum 12" between panel end and diverter on the upslope 

o Minimum 6" between the curb sides and panel seams 

• Use rib-to-rib curbs 

• Never use blocking made of dissimilar materials, such as treated lumber, in conjunction with any curb. 

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