REPAIRING AN EXISTING 36-INCH LAMINATED ASPHALT SHINGLE ROOF WITH METRIC-SIZED LAMINATED ASPHALT SHINGLES
Guide for trimming metric shingles to repair roofs with standard-dimension laminated shingles
When older laminated asphalt shingle roofs need repair, roofing contracts face a practical problem: the 36-inch shingles originally installed are no longer manufactured. Today’s laminated shingles are produced in metric sizes, which are nominally one meter long and approximately one-third meter wide. Their weathering exposures are roughly 20% larger than their predecessors.
That size difference raises legitimate technical questions. Can a reliable, weathertight repair be made? Will the nailing patterns align? Does wind resistance hold? Are there aesthetic or code compliance concerns?
Haag Research & Testing set out to answer those questions through controlled testing.
The Research
This technical paper documents a comprehensive investigation into repair compatibility between legacy 36-inch laminated asphalt shingles and modern metric-sized products. Haag Research & Testing acquired discontinued bundles of 36-inch shingles and systematically evaluated multiple repair approaches using metric shingles, including trimming techniques, fastener placement, adhesive application, and alignment strategies.
Testing was conducted using Haag’s wind generation equipment to assess the wind resistance of completed repairs — a critical factor in roofing forensics, insurance claims analysis, and construction defect disputes.
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