MBMA Compares Retrofit Systems for Existing Metal Roofs

The Metal Building Manufacturers Association (MBMA) released the white paper, “Comparison of Retrofit Systems Over Existing Metal Roofs,” by Brian Gardiner FRCI, RRC, CCS. This paper provides a detailed comparison of two options for putting a new roof layer over an existing metal roof: a new metal roof and a single-ply layer, often consisting of Thermoplastic Polyolefin (TPO).
When a metal roof has reached the end of its lifespan, one option is to retrofit the roof; that is, construct a new layer of roofing material on top of the old one. Brian Gardiner makes the case for why this is a good option, then goes on to compare two retrofit methods in this white paper.
“With the popularity of retrofit roofing growing, there is a need for information to educate roofers and building owners about the code requirements for re-covering roofs,” notes Dan Walker, MBMA associate general manager. “This paper helps to fill that gap.”

Comparison of Retrofit Systems Over Existing Metal Roofs first looks at the building code requirements in the International Building Code (IBC) and International Existing Building Code (IEBC). The paper explores the specific sections and provisions of both codes that come into play before moving on to the building and design considerations.
There are a number of design considerations that should be accounted for when deciding which retrofit option is best. These include the existing support structure of the building, secondary structural member deflection, existing metal roof properties, ponding water, fastening the retrofit roof to the existing structure, drag load and fire rating.  The paper provides details about both metal roof and single ply retrofits for each of these considerations. The paper’s summary also notes that, when considering retrofitting a metal roof, owners and builders should engage a licensed professional engineer to indicate the best way forward and consult with local code officials to determine what is acceptable for buildings in the area.

“This white paper provides information about the options for retrofitting a metal roof,” notes W. Lee Shoemaker Ph.D., PE, MBMA’s director of research & engineering. “Before undertaking a project of this nature, it is important to research all the information available before making any decision. This paper is a good place to start.”
To download the white paper, visit here. For more information about metal roofing or any of MBMA’s research and education initiatives, please contact [email protected] or call (216) 241-7333.

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