Research Study Shows Certain Metal Roofs Can Last at Least 60 Years
“This study is a breakthrough for the metal construction industry because it finally provides third-party, scientific data that backs up the long held stance that 55 percent Al-Zn coated steel standing seam roofing systems are very durable, economic, and can be better for the environment,” said Scott Kriner, Technical Director, Metal Construction Association. Most non-metal roofing systems require one or more full replacements within a typical building’s 60-year service life, which is costly and often adds to the solid waste stream in landfills.
The study, sponsored by MCA and the ZAC Association, was conducted with oversight of three independent consulting firms which analyzed low-slope, unpainted 55% Al-Zn coated steel standing seam roofing, in a wide range of environments across the U.S.
This type of roof material is known by many trade names throughout the world, principally GALVALUME and Zincalume in the United States. It is very common on low rise commercial buildings such as warehouses, schools, distribution centers, shopping centers, exposition halls and other facilities. Experts estimate that the market size for this type of low slope roofing in the U.S. is over 350 million square feet.
The study incorporates the results of multiple field inspections, independent laboratory analyses of metallic corrosion of the roof panels, components and sealants, and includes assessment of all integral ancillary components that impact the end of roof service life.
The research team selected 14 building sites in five climate regions of various geographies in the continental United States, exhibiting a spectrum of climates related to heat and humidity including Hot-Dry, Hot-Humid, Cold-Dry, Cold-Humid, and Moderate-Acid. The precipitation acidity also varies considerably from one site to the next over this broad geography.
The research study concluded that the expected service life of an unpainted 55 percent Al-Zn coated steel standing seam roof constructed today in a wide range of environments using best practices can be expected to be in excess of 60 years, a value that equals the assumed building service life as described in the USGBC’s Leadership in Energy and Environmental Design building rating program, version 4.
In the study, the steel panel roofs experienced corrosion rates that conservatively project service lives well beyond the service life of most buildings. The range depends on the climate and the local precipitation pH.
The study also confirmed that these types of metal roofs resist corrosion even in “weak” spots, such as sheared edges and panel profile bends. Inspections showed an absence of significant red rust after up to 35 years, indicating exceptional corrosion resistance in areas susceptible to exhibiting the first signs of corrosion.
The study acknowledges that all roof systems require a regular maintenance program (at least annually) to clean off debris and to inspect the condition of the roof in order to achieve the kind of service lives shown in this study. While low-slope steel standing seam roof systems were projected to last up to 60 years, ancillary components (such as fasteners) may need to be replaced during the roof life, but this represents significantly less than 20% of a total roof replacement cost.
“We are planning to conduct more studies on different types of metal roofing, and in some cases we expect similar or even better results in terms of roof service life,” adds Kriner. “We think these studies will help to motivate building owners and architects to specify metal roofing more often.”
The report was authored by Ron Dutton, Ron Dutton Consulting Services LLC; Rob Haddock, Metal Roof Advisory Group; Chuck Howard, Metal Roof Consultants and Scott Kriner, Metal Construction Association. The report was also peer reviewed by Morrison Hershfield laboratory in Canada.
