Every roof system needs a flashing system that works. Poor
flashings have allowed water to get in and under the best of roof
systems. Sometimes, water entry is attributable to an improper
design detail; other times, it may be a problematic application.
Often, flashing material fails because of the demands of direct
weathering, differential movement, inadequate attachment,
cumulative movement or other stresses. Spray polyurethane foam
(SPF) roof systems are unique because of the direct use of SPF
material as the flashing system.
For example, a roof mechanic applying SPF material literally
applies SPF up a wall, curb or projection to a prepared elevation
and stops. Flashing sheets and fasteners are not required. The use
of metal as a counterflashing over SPF material and coating also
may be used. Currently, The NRCA Roofing and Waterproofing
Manual, Fifth Edition's construction details call for SPF roof
systems to use metal counterflashings. This article addresses what
is happening in the field with SPF flashing details that do not
incorporate metal counterflashings.
The use of SPF on roof systems began in the 1960s. But getting
SPF recognized by the industry as a viable roofing material took
some time. As a result, a number of independent studies of SPF roof
systems had been conducted during the 1980s and early 1990s; papers
about the studies can be found in the proceedings of the second and
third International Symposiums on Roofing Technology (log on to
shop.nrca.net to purchase
the proceedings). And the Spray Polyurethane Foam Division, now
known as the Spray Polyurethane Foam Alliance (SPFA), developed a
contractor accreditation program that continues to publish
technical bulletins about the design, use and installation...
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