Can Metal Be Installed Over Two Layers?
Dean wrote and asked me:
Q: My cottage has one layer of shingles. But my detached garage has two layers. They are getting very old with mold growing on them and are curling in spots. Is it advisable to install metal shingles over the existing layers of asphalt singles?
A: The low weight of metal roofing encourages such an application. Small amounts of curling are usually not a problem and a layer of underlayment is installed over the old shingles to minimize the impact of such curling.
Any biological growth will die once it is isolated from moisture and sunlight.
However, the building code in your area may dictate no more than two layers of roofing. Often even in those cases, though, building inspectors will waive the two layer maximum rule once the understand the low weight of metal.
Todd Miller has spent his entire career in the metal building products manufacturing industry. He is president of Isaiah Industries, an organization recognized as one of the world’s leading metal roofing manufacturers. Todd is currently Vice President of the MRA (Metal Roofing Association) and a Past Chair of MCA (Metal Construction Association). Through his website, he strives to raise the bar on standards and practices to provide property owners with the best possible products for successful roofing projects.
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