Coating of Asphalt Shingles After Installation
ARMA strongly advises against the application of any type of field-applied coating over installed asphalt shingles. There are many types and formulations of roof coatings so it is important to always consult the shingle manufacturer before proceeding with any type of coating. Be aware that some asphalt shingle manufacturers specifically disallow field coating of their shingles. Additionally, state or local building codes may not approve this practice as the field applied coatings may change the performance characteristics, including the fire classification, of the roof assembly.
Problems reported after asphalt shingle roofs have been field coated include shrinking of the coating, which may result in unsightly curling and/or cupping of the shingles, or loosening of the granule surfacing of the asphalt shingles. In addition, non-permeable roof coatings may create a vapor retarding layer by sealing the voids around and between the shingles. If this occurs, it increases the possibility of rotting of the roof deck caused by moisture accumulation in the attic space.
It has been suggested by some that the use of field applied coatings over existing asphalt shingles will produce overriding benefits to the home owner — such as longer roof life, energy-use reduction, or remediation of small roof leaks. There is little or no available documentation showing the extent to which the field coating of asphalt shingles provides any of these benefits, but the risks and concerns mentioned above remain very real.
Before considering coating of installed asphalt roof shingles, be sure to:
• Obtain approval from the asphalt shingle manufacturer before proceeding with a specific roof coating.
• Check with the local building and zoning department and, if appropriate, your homeowner’s association to determine whether this application is allowed.