Thirty years ago, in 1991, my partner Red McConnohie had an idea to create a retrofit system that would allow you to put a new metal roof over an old worn-out metal roof. Red and I formed a fledgling company and set out to market our new and better product to other contractors and erectors.
Soon enough we started getting questions like “How do we know this is a structurally correct assembly?” Good question I thought, how do we confirm our retrofit system is as strong as we knew that it was? We had a design engineer but in the early 1990s there was no standard test for what we were doing, we had pages of calculations but no actual tests. So, we called our engineer for some ideas on how to conduct testing.
Let’s build a roof section, he said, turn it upside down and stack concrete blocks on it until it collapses. We weigh the blocks, and then we’ll know at what load the system fails. Great idea we thought so off we went to create a mockup and test it. The system didn’t perform quite like it calculated but not too far off and we had some actual data points!
By the late ’90s test labs were getting more sophisticated and we did some additional confirming tests, using the latest equipment. Now we had even more data points to compare to our early rudimentary testing.
In the early 2000s, a new test was becoming the industry standard for testing and for code compliance. This new test was the ASTM E-1592. Although testing for through fastened panels was not considered necessary and calculated values were still being used, there was no precise way to determine the capacity for the newer standing seam panels. The E-1592 test was developed to test standing seam panels, although it can test both types. It basically places a flexible air bag beneath the panel and air pressure is gradually added to this air bag pushing the panel up until it fails. Very aggressive but a reliable test, which soon became the industry standard.
This was the best test ever for our system because now we could have real performance test data with the sub-framing system and the actual new roof panel (or similar) in a real-world assembly. The testing confirmed what we had discovered from our earlier tests, that the systems do not test as well as they calculate. However, this was good news, since now we had actual performance data! The only problem is that there are hundreds of new and existing panels in the market. Fortunately, many panels are very similar and can be grouped for analysis, but a significant amount of testing still had to be conducted. With this knowledge, we set about the business of testing the major groups including screw-down roofs, vertical rib standing seam, trapezoidal standing seam, deep rib systems, tall clip assemblies, corrugated panels and more.
Today’s challenges are even more complex. We always knew that the notched framing systems added additional weight to the building, we also knew they added additional strength to the existing purlins, but to what extent? The existing building code allows an additional 3#’/s.f. of additional loading without a full building analysis, which will cover most building retrofits; however we also knew this research would be important because in some cases the existing buildings were already loaded to their maximum. This was an interesting and challenging question since no real test protocol existed to make that determination.
In 2018, we began the first ever Base Testing for a retrofit system on continuous purlins. This required the construction of a 50-foot-long chamber and many combinations of parts and pieces. The results are in and very positive. Modeling of the results is being undertaken currently.
This is great news for the designer/specifier. Retrofit metal roofing has come light years from its humble beginnings. Shirt sleeve engineering has progressed to full system performance engineering with predictable results. Makeshift assemblies are recognizable for their short comings and lack of confirming test data.
The truth is that all roofs will wear out at some point, even long-life metal roofs. When that time arrives, it is good to know that you can specify with confidence a system that will upgrade the existing building’s old roof to the current building codes, can last up to 60 years, add energy efficiency and be the ideal platform for future photovoltaic systems.
Dale Nelson is the president of Roof Hugger LLC, Tampa, Fla. A division of the LSI Group, Logansport, Ind., Roof Hugger is a manufacturer of retrofit framing systems for existing metal roofed buildings. To learn more, visit www.roofhugger.com.