Wind-tunnel research on unsealed shingles
by Thomas L. Smith, AIA, RRC
Last year, a consortium of
NRCA and four asphalt
shingle manufacturers
initiated a project to test unsealed asphalt shingles' wind-tunnel performances. The research project took place during March and April at Colorado State University, Fort Collins.
Good wind performance of self-sealing shingles
largely depends on
a shingle's adhesive bond's integrity and resistance.
However, before
the sealant activates (which requires relatively high temperatures), some roof systems are exposed to moderate winds.
For example, shingles installed in the fall or spring may remain unsealed for a few days or even months before the sealant becomes warm enough to activate. Another example is a roof system that is installed during a summer day and, before the sealant bonds, is subjected to a
thunderstorm.
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Photo 1: At the end of testing, these fiberglass-reinforced asphalt shingles did not show any significant signs of damage.
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When self-sealing shingles experience moderate wind loads before sealant activation, they are vulnerable to damage. The potential for damage, such as tearing near fasteners, fastener pull-through or tab
tearing, is related
to a number of factors, including fastener location, the
shingle's fastener
pull-through resistance, shingle pliability and overall
product strength.
The research
aims to establish
a correlation between unsealed shingle damage and a small matrix of factors. These factors include different shingle designs (i.e., three-tab organic-reinforced; three-tab and laminated fiberglass-reinforced; and three-tab SBS-modified); shingles with different physical properties (e.g., fastener pull-through resistance, tear strength, flexibility); different attachment designs (i.e., four and six nails); and application variables (i.e., fasteners in the correct location and those placed high).
Performance variations
NRCA obtained 30 bundles of shingles for initial laboratory characterization. Based on this lab work, two organic, two three-tab fiberglass and two laminated fiberglass products were selected for the wind-tunnel evaluations.
Photo 2: At the end of testing, most of these laminated shingles were blown off.
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To evaluate temperature influence on shingle performance, samples were tested at about 70 F (21 C) and 35 F (2 C).
During the wind-tunnel work, significant performance variations were observed. Some test assemblies did not exhibit significant damage (see
Photo 1), while others were damaged severely (see Photo 2).
Variations also
were observed
among assemblies
constructed with
shingles from the
same lot. Typically, four replicate
assemblies were
evaluated for each
condition type. Often, one or more of the four replicates were not damaged; yet, one or more of the other replicates were damaged. This variation may have been caused by differences in material characteristics between one shingle and another and/or minor variations in fastener location. These variations will be evaluated during the data analysis.
High fasteners
On some of the laminated shingle
assemblies, the nails were about 1 to 1½ inches (25 to 38 mm) above the nailing line. In the correct location, the fastener penetrated a double thickness of material at the laminated area; however, when the fastener was nailed high, it only penetrated a single thickness. Nailing high resulted in decreased wind resistance.
One of the laminate products had a small material overlap at the nail line. Even with the nail centered on the nail line, there was little edge distance between the nail shank and edge where the single thickness began. With this product, if the nail was only slightly high, it would miss the area of double thickness.
Summing it up
This research project showed a significant range in unsealed asphalt shingles' wind-tunnel performances. Data analysis is underway and will be available later this year; it should help roofing manufacturers and contractors when manufacturing, selecting and installing self-sealing asphalt shingles.
Thomas L. Smith is NRCA's research
director.
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