The following article was featured in Coil World.
In 1972 a new coating for metal roofs was introduced by Bethlehem steel. It was called Galvalume® since its make-up was mostly zinc and aluminum. Zinc had proven itself over the previous decades when applied to a steel roof sheet with a process called galvanizing. The zinc sacrificed itself to flow over edges and any other exposed portion of the base steel sheet, giving it protection for many years, usually in the 20 to 30 year ranges. Aluminum coatings to metal roofs had recently proven to protect the base metal materials in a superior fashion, but did not “flow” like zinc and, therefore, had little protection capability on the cut edges and imperfections inherent in sheet metal that had to be cut and formed into a roof panel. In the 1960’s Bethlehem Steel’s engineers and metallurgists designed and exhaustively tested a formulation and process to get the best of both the zinc and aluminum product to provide a superior coating for a steel sheet that would ultimately be made into a metal panel. They called it Galvalume® and introduced it to the metal roofing industry, guaranteeing it to protect the steel sheet for twenty (20) years.
In part one of this article series, written by Ron Dutton, it was explained how a recent and ongoing study of actual Galvalume® coated roof panels have performed over the last 25 to 35 years. This informative article clearly makes the scientific statement that these roofs, in the real world, are faring much better than the Bethlehem engineers and metallurgists assumed in the 1960’s. In fact, they are outperforming their expectations by a considerable amount. In the non-coastal regions of the United States, this study confirms that these panels should expect the Galvalume® coating to protect the roof panels for a minimum of 60 to 80 years with realistic expectations of many to last over 100 years.
Retrofit Metal Roofing (RMR) History
In the late 1970’s a roofing process to convert a flat roof to a sloped metal roof was developing. This process allowed contractors to assist building owners to create slope on their flat roofs, eliminating the constant problem associated with water ponding on their roofs, and to use a metal roof system that would collect the water exposed to their roof areas and drain it to the edges of their buildings for discharge off of the roofs. This process created a perfect fit for the application of standing seam metal roof panels using the newly introduced Galvalume® coating. While the infant retrofit metal roofing market was developing, it was always assumed that these roofs would last at least as long as their 20 year bonded built-up-roof competition. The big advantage of this new process was sold as the ability to eliminate ponding and get the water off the roof quickly, before it could find its way into the building interior.
Fast forward, now, to 2013. We now have scientific proof that these Galvalume® coated metal retrofit roofs have not only added slope, they have allowed for the use of a roof panel coating to be used which will far exceed the expected life of the then popular 20 year bonded built-up-roof. This testing is now confirming that less than 25% of their protective coating life is expired by the time 100% of the flat roof membrane has expired.
The RMR process is simple in concept. A light gage steel framing system is retrofitted onto the existing flat roof, providing a new sloped plane on which to install a standing seam metal roof. The framing system is anchored to the existing roof structure by attaching a base clip or shoe to the existing structural roof framing. This base clip sits on the original roof, with fasteners penetrating this roof into the roof structure. A variable height light gage steel post is then attached to the base clip to support a light gage steel purlin, creating the support plane for the metal roof panel. All of this new framing system must be braced properly in order to transmit the roof loads consistently into the existing structure. It is mandatory that this system, including the attachment to the existing structure, be designed by a licensed professional engineer in the state in which the project resides. Per the current International Building Code (IBC), accepted by most state building departments, the existing roof (s) do not need to be removed due to the fact that the light gage framing system and metal roof are collecting the roof loads and introducing them directly into the existing roof structure, eliminating any live load being applied to the original roofing assembly.
When this process was being developed, the necessary components where easily found in the components associated with the metal building industry. The light gage framing system is composed of mainly 16 gage red-primed 4″ and 6″ C and Z shapes, which can be roll-formed by metal building manufacturers and many metal roofing manufacturers. The metal roof panels and their accessories (trim, gutters, downspouts, etc.) are also manufactured by computerized roll-forming machines and breaks. Of course, the base material for the metal roof materials is predominately Galvalume®. The use of this covering material will protect the structural components, as well as the building interior, for as long as the building will last. Pretty impressive, wouldn’t you say?
Life Cost Analysis of RMR
The Athena Sustainable Materials Institute has established an “assumed building service life” of 60 years. The recent Galvalume® metal roof study referred to in the first article in this series, sponsored by the Metal Construction Association (MCA), the Zinc-Aluminum Coaters Association (ZACA), and the American Iron and Steel Institute (AISI), show that one (1) Galvalume® coated standing seam roof will perform well beyond the established 60 years of “assumed building service life”. In comparison, there are no commercially available flat roof materials that are projected to even come close to lasting 60 years. A recent straight cost analysis of a school roof in the mountains of Virginia, where their experience indicated that their flat roofs were lasting 15 years at most, it was demonstrated that installing a sloped retrofit metal roof over a flat roof will cost approximately half of what it would cost to continue with their flat roof over the next thirty (30) years (see chart). Due to these dramatic facts, this small district made the decision to use their limited resources in a prudent manner, knowing that the “life cost” of their roofs is more financially important than the “initial cost”. The roof life cost analysis for this school district is not an exception, but rather consistent with all roof life cost analysis comparisons between one (1) sloped Galvalume® standing seam roof and multiple flat roofs in a time span of thirty (30 ) years or more.
A Successful RMR Experience
A successful RMR experience, adding slope to a flat roof with a standing seam metal roof system, is possible in almost all instances. The stigma that these roofs are “too expensive” is simply not true when analyzing the roof cost using a life cost analysis method. And, why shouldn’t that method be the primary basis for all projects where buildings will be performing for 60 years or more?
A successful RMR experience consists of more than roof panels and framing. It requires a properly executed process in order to receive the entire benefits of this roofing system. The main components of this process are as follows:
1. Design – This system is a structural system that needs to be designed by a licensed professional engineer to meet the applicable building code laws in the jurisdiction where it exists. This means that a licensed PE that is familiar with light gage framing and roof loads should be involved with the design of these systems, as they relate to the particular roof and the local area. Per the IBC, the existing roof only needs removal in a few extreme cases, the wind pressure needs to be calculated using the current edition of the ASCE 7 manual, and the roof system panels need to be analyzed using the ASTM E 1592 standard test. In addition, the capacity of the existing roof structure needs to be analyzed to verify that it can support the new retrofit roof plus the current wind and snow loads.
2. Materials – Only metal roofing materials that are suited for this type of roof assembly should be used. There are numerous metal roofing suppliers that manufacture a structural standing seam roof system, capable of spanning between the purlins of the retrofit system used to create slope. Also, only panels that have been properly tested to determine their load limits, per ASTM E 1592, should be used.
3. Installation – This system must be installed by an experienced contractor who will insure that it is erected per the design and manufacturer’s instructions. If those conditions are met, the roof renovation will be a success.
A retrofit metal roof system, using a Galvalume® coated standing seam roof will eliminate the ponding problems of a flat roof and cover the system and the building with a metal roof panel that will last well beyond its “assumed service life”. It needs to be designed properly, use concisely manufactured products, and be installed as it is designed. When those components are in place, a building owner can expect to have a great experience with his roof, instead of having to deal with it, financially and with frustration, for years to come.
The author thanks MCA, AISI and NAZA for jointly commissioning the Galvalume® study, and the privilege to help Ron Dutton and Rob Haddock perform the field work. The full report is expected to be published in 2013. For further information about retrofit metal roofing, please visit the author’s website, www.metalroofconsultants.net.