20 Years of Metal Retrofit Roofing
“You can’t do that.” That was my response to Jim Shoemaker in early 1979 when asked if I could convert a portion of his flat roof to a pitched metal roof. Jim was president of Bennett Metals, Wilmington, Ohio. I had just completed an addition to his flat-roofed concrete building using a single-sloped metal building with a metal standing-seam roof system. Jim’s request came because he was continually moving finished products out of the existing building area, where they were being damaged by water from roof leaks, into the new metal building, where the interior space was being kept dry by the new metal standing seam roof.
After many more requests from Jim, I finally agreed to at least look at the possibility of adding pitch to an existing flat roof. In October 1979, I signed a contract with Bennett Metals to add pitch to a 40-foot by 40-foot roof area and install a new metal standing seam roof. The work was completed in early 1980 and Jim Shoemaker now had a dry area in his existing building where he could store finished product.
Getting StartedWhile the Bennett Metals project was successful for both them and me, it wasn’t until over a year later that metal retrofit roofing became important to me. It was April 1981 and we were in a construction recession in the Ohio market. My small general contracting company had no backlog. I thought back to the satisfaction of Jim Shoemaker with his metal retrofit roof and decided to introduce that concept to some of my past customers. I mailed a one-page letter to 100 potential clients and received an astounding 26 responses. We received six contracts to design and install metal retrofit roofs. In December of this same year, I received a negotiated contract to retrofit a 110,000-sqaure-foot flat roof for Tube Products located in Troy, Ohio. These occurrences started me on a new career path, which I am still on today. They also were part of the initialization of the metal retrofit roofing market.
20 Years LaterIn November and December 2001, after 20 years of actively pursuing metal retrofit roofing work, I marketed this concept at four different state school board conventions. Having received more than 60 personal requests for more information on this roofing concept (from specific jobs to bid to just wanting more information), I can attest that the demand for this type of roofing is still strong. The basic concept of converting flat roofs, with ponded water and all of the associated problems, to slightly pitched roofs is very well received by school board members and school superintendents. They view this roofing approach as a permanent solution to their flat-roof problems.
Metal Retrofit Roofing ConceptThe basic concept of metal retrofit roofing is that slope can be added to any roof surface. Some are dead flat, some slope to drains, some have a slight slope to a roof edge. The metal retrofit roofing procedure includes the following components that allow the conversion to a positively sloped roof surface:
Base clip: a base clip and/or base runner is attached to the existing roof structure. In most cases the existing roof membrane can stay in place between the base clip and the existing roof structure.
Variable height post: a light-gauge structural post is cut to whatever length is necessary to support a roof purlin at the necessary elevation.
Purlin: a light-gauge purlin is attached to the top of adjacent posts, running perpendicular to the new roof panel direction.
Banding and bracing: necessary steel banding and eave and ridge bracing is necessary to structurally hold the light-gauge system in place.
Roof panels: a standing seam-roof system is installed on the new roof plane created by the subframing system. This roof system can have either a basic galvalume coating for low-sloped applications (less than 1:12), or have a baked-on painted coating over the base galvalume for the higher pitched and more visible applications.
Accessories: gutters, downspouts, trim, wall panels, soffit, etc., are added to the roof system to provide a finished appearance and cover areas created by the addition of slope to the existing building.
While the basic concept is simple, the structural components of the entire system need to be analyzed and designed by a structural engineer familiar with this type of framing. That analysis should include the existing building structure. The total composite system needs to be able to adequately handle all loads identified by codes in the area where the building is located.
Metal Retrofit Roofing PerformanceMetal retrofit roofing is a system that performs exceptionally well over a long period of time. The basic concept of this type of roofing — adding slope to an existing flat roof — eliminates a majority of the problems with the original roof. The addition of a steel weathering skin that has been in the commercial roof market since 1932 assures that the water will get to the perimeter of the building instead of ponding on the flat roof surface.
That is not saying that this system is perfect. As with all field-assembled construction systems, there is always room for error. With a metal retrofit roofing system, however, that possibility is small. As long as the metal panels are installed with the “ribs up,” the only place in which water can intrude the interior space is where the panels stop. At those locations (curbs, eaves, ridges, rakes, laps, etc.) properly applied caulk between the metal surfaces and properly installed fasteners with weather seal washers can assure a permanent weathertight condition. It is always possible that one of those conditions needs attention after the roof is complete. However, it is easy to locate such a condition and fix it. When the entire system is finally tightened up, it will continue to resist water intrusion for many years.
With respect to how long this system will continue to perform, I can offer my first hand experience. Companies I have been responsible for have designed and installed over 9 million square feet of metal retrofit roofing since my first experience at Bennett Metals in 1979. To my knowledge, all of the metal retrofit roofs with which I have been associated are still in leak-free service for the owners today. While I cannot account for every job, several hundred thousand square feet have lasted more than 20 years. The Bennett Metals and Tube Products projects are examples of work in this category. Properly designed and installed, using quality products from a reputable manufacturer, a metal retrofit roof should perform for a period exceeding 20 years.
Weathertightness WarrantiesMost roof material manufacturers provide a weathertightness warranty program for the building owner. These warranties vary in length, but predominately cover a 20-year period. The maximum liability of the warranty varies with each manufacturer and there are alternate pricing structures for increased liability. All plans that I am aware of require the installing contractor to be responsible for the weathertightness of the roof for the first two years. The manufacturer will then pick up the remaining 18 years on a 20-year weathertightness warranty. These warranties have been available since the early 1980s.
Last year I contacted five of the major suppliers of metal roofing materials that also provide weathertightness warranties for the installed systems. The purpose of my inquiry was to determine the financial impact of the weathertightness warranty programs. The results were very consistent among the manufacturers contacted. There were no instances of roof removal and replacement. The costs associated with warranty claims were very small (in the thousands of dollars) per incident and the incidents were sporadic and incidental. While the fact that the results were not readily available due to the lack of incidences was discouraging, it was very encouraging to know that the industry, as seen by these manufacturers, mirrored my own personal experience with respect to weathertightness.
Material WarrantiesAs stated earlier in this article, the metal-roof weathering surface would have either a galvalume or painted finish. Both of these exposed surfaces carry a standard 20-year warranty direct from the steel producer for galvalume and the paint supplier for painted. The painted surface would have a coat of paint baked on the steel sheet prior to forming into a roof panel. This steel sheet would already have a galvalume coating. The paint used to bake on this steel coil would have a Kynar additive that provides for longevity with respect to peeling and flaking as well as fading. This additive has performed well in the metal roofing market for well over 20 years and has carried a 20-year warranty on it during that time period. Some paint suppliers are starting to offer paint warranties that exceed 20 years, based on the past performance.
With respect to the galvalume coating, this product has been used for protecting the base metal since the early 1970s. The Galvalume Sheet Producers of North America’s recent publication, “Galvalume Standing Seam Roofs, Proven Performance – 25 Years and Beyond,” indicates that galvalume-coated metal surfaces in many different atmospheres have lasted 25 years and should last at least another 10 to 15 years. The coating is a mixture of zinc (45 percent) and aluminum (55 percent). The zinc allows the coating to heal itself over time from minor abrasions and cut edges, while the aluminum provides the basic protection to the base steel from air, water and their contaminants. This combination provides a coating that will protect the metal roof panel well beyond its warranted life of 20 years.