Coating of Asphalt Shingles After Installation
Many types of roofing permit the application of a coating for a variety of reasons, such as
increasing solar reflectivity, resisting biological growth, improving impact resistance, or
increasing roof life. However, 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 always important to consult the
shingle manufacturer before proceeding with any type of coating. Many asphalt shingle
manufacturers specifically do not recommend field coating of their shingles. Additionally, state
or local building codes may prohibit this practice, as the field-applied coatings may negatively
impact the performance characteristics (including the fire classification, algae resistance,
impact resistance, etc.) of the roof assembly.
Some of the 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 may contribute to moisture accumulation within the roofing system.
It has been suggested by some that the use of field-applied coatings over existing asphalt
shingles will produce overriding benefits to the homeowner, such as longer roof life, energy-use
reduction, or remediation of small roof leaks. There is limited 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. Further, many coatings need regular
maintenance reapplications to provide a consistent appearance.
In summary, the application of a coating may be detrimental to asphalt shingles. Be sure to:
• Check with the asphalt shingle manufacturer before determining a specific roof
• Check with the local building and zoning department and, if appropriate, your
homeowner’s association to determine whether this application is allowed.
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