Research Finds Sub-purlin Systems Increase Roof Load Capacity

Roof Hugger Sub-purlin Systems
February 1, 2023 at 6:00 a.m.

By Evelyn Witterholt. 

After extensive research and tests, Roof Hugger found that their sub-purlin systems enhance existing weight capacities on roofs. 

When sub-purlin systems were on the rise in the '90s, there were concerns amongst the roofing industry of the additional dead load risks. Although roofing contractors liked that sub-purlin systems were easier to install for retrofitting roofs, they were concerned about whether or not it would strengthen the roof.  

Enter Roof Hugger, a trailblazer in the world of metal-over-metal retrofit systems. They knew that the nesting design and secure connection of sub-purlin systems added strength to roofs, but they didn’t quite know how much. So in the early 2000s, they underwrote a series of research tests from the Farabaugh Engineering and Test Labs in Turtle Creek, Pennsylvania to get answers for the industry’s burning questions. 

In these tests, their overall objective was to see if there was any positive load moment capacity as well as enhanced flexural stiffness with installing sub-purlin systems. They specifically tested nesting Z sub-purlins with new roof panels on top. Their results were overwhelmingly positive. 

In an article from Metal Architecture, Roof Hugger Inventor, D.V. McConnohie writes: “In sum, the average added dead load of a new roof-over is 1- 1/4 to 2 pounds per square foot (psf), whereas the data indicated an increased capacity of 7 to 15 pounds psf depending on the standard web height of notched sub-purlins used in the tests.” 

The results of the tests also found that Roof Hugger’s sub-purlins when installed with a double roof diaphragm assembly on the locked down original roof panels and supports offers added torsional and lateral stability. McConnohie writes: “The component manufacturers, metal contractors and erectors, as well as the professionals designing and specifying reroof projects, can now attest to the safety as well as the cost savings of retrofitting to aid the growth of this relatively new mass market.” 

Read the entire article here to learn more about the research findings of the benefits of using sub-purlin systems.  

Have a question? AskARoofer.   

Find your local roofing contractor in the RoofersCoffeeShop® Contractor Directory  

Image credit: Metal Architecture 

About Evelyn  

Evelyn works as a writer for RoofersCoffeeShop, MetalCoffeeShop and AskARoofer. When she isn’t writing about roofing, she’s either at the gym lifting weights or curled up on the couch watching a movie.

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