Recommendations for Application of Asphalt Shingles on Slopes Greater Than 21:12

The maximum slope considered by ARMA to be suitable for normal asphalt shingle application is 21:12, or 21” per foot. The use
of asphalt shingles on slopes greater than 21:12 (e.g., mansard roofs) requires the use of special application methods because
very steep slopes reduce the effectiveness of factory-applied self-sealing adhesives, especially in colder climates and shaded
areas. If normal application methods are used for asphalt shingles on very steep slopes, problems can occur that are not a result
of any weakness or defect in the product, but rather because special application methods for very steep slopes were not
If a roof slope exceeds 21:12, the shingles should be applied by the following recommended method:
 Secure the shingle to the roof deck with fasteners as directed by the roofing manufacturer. Manufacturer directions may
call for more than the normal number of fasteners per shingle and may provide specific fastener locations.
 Apply a manufacturer-recommended asphalt roof cement complying with ASTM D4586, Standard Specification for Asphalt
Roof Cement, Asbestos-Free, or other cements approved by the roofing manufacturer under all shingle tabs in spots
equivalent to the size of a quarter (about 1” diameter), immediately upon installation.
o For standard laminated shingles (i.e., ‘no cut-out’ shingles) apply four spots of cement under each shingle near the
lowermost edge, with two near the corners and two equally spaced between the corners.
o For ‘three-tab’ shingles, apply two spots of cement under each tab near the lowermost corners.
o For other specialty shingles, refer to manufacturer’s recommendations.
 Over-application of adhesives is not recommended; follow manufacturer’s recommendation for cement type and minimum
and maximum quantities.
 An unvented space may be behind a mansard roof. It is important to provide a properly ventilated flow-through air space
behind the roof sheathing to prevent the entrapment of moisture-laden air. Additional information is available on ARMA’s

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