SPF flashings and through-wall flashings | Manual Elements
NRCA first provided technical information for spray polyurethane
foam (SPF)-based roof systems in the fourth edition of The NRCA
Roofing and Waterproofing Manual in 1996. There were 25
SPF-based construction details included. In the fifth edition in
2001, the text was updated and additional construction details were
added. There currently are 32 SPF-based construction details-27
with elastomeric coating and five with membrane coverings,
including SPF-5, "Base Flashing for Wall-supported Deck," which
provides SPF flashing, metal reglet (also known as through-wall
flashing) and counterflashing information (see figure).
The counterflashing is installed after the installation of spray
polyurethane foam (SPF) and coating. The coating should extend
about 2 inches (50 mm) above the foam's top edge, which should be 6
inches (150 mm) minimum in height, and the counterflashing ideally
should cover the location where the foam terminates.
For the through-wall flashing to perform properly, the foam and
coating must not cover the counterflashing, reglet and weep holes.
Through-wall flashing is used where moisture is likely to penetrate
the wall system. For example, masonry and stucco walls typically
incorporate through-wall flashing at the interface of the roof
flashing and wall covering. Through-wall flashing directs moisture
that penetrates the wall system toward the roof surface, preventing
the moisture from entering the building and decreasing possible
deterioration of the substructure. The use of weep holes allows
trapped moisture to escape the wall system. NRCA does not recommend
sealing the joint between the through-wall flashing and wall
covering; this reduces the ability for moisture to escape the wall
system.
In the manual's fourth edition, the through-wall flashing and
counterflashing were depicted with a 3-inch (76-mm) overlap seam;
the through-wall flashing also included a single bead of sealant.
SPF-5 in the fifth edition does not provide specific direction for
joining the through-wall flashing and counterflashing. To
accommodate the multiple accepted methods of joining sheet metal, a
Sheet Metal section now is included in the Construction Details
section of the fifth edition. Common joints are depicted in SM-26;
the lap seam and cover plate seams are appropriate joinery methods
for SPF-5, and NRCA recommends installing sealant in the laps of
the metal. The through-wall flashing/sheet-metal reglet and weep
holes typically are installed by a masonry contractor. The
counterflashing is installed by a roofing contractor. The
through-wall flashing and counterflashing material may be supplied
by either.