Spray polyurethane foam- (SPF-) based roof systems require protective surfacings to provide long-term weatherproofing. The most common surfacing for SPF-based roof systems is an elastomeric coating, but a membrane surfacing occasionally is installed over SPF. In those circumstances, the SPF functions solely as roof insulation. Membranes over SPF can be fully adhered or loose-laid and ballasted.
This month's detail features a plumbing vent penetration in an SPF-based roof system incorporating a fleece-back membrane. A nonwoven fleece backing is adhered to the underside of a membrane to separate the substrate and/or facilitate adhesion. The fleece-back membrane is adhered to the SPF with low-rise polyurethane foam adhesive.
Adhered membrane surfacings used in SPF-based roof systems should be 100-mil- (0.1-inch- [2.5-mm-]) thick minimum, composite EPDM thermoset membranes—a 45-mil- (0.05-inch- [1.1-mm-]) thick sheet bonded to 55-mil- (0.06-inch- [1.4-mm-]) thick fleece. The EPDM membrane sheet should meet requirements of ASTM D4637 "Standard Specification for EPDM Sheet Used in Single-ply Roof Membrane."
SPF-18 (FB) also illustrates a premanufactured boot. Flashing boots commonly are used by roofing contractors because they are seamless (weathertight) and easy to install. NRCA recommends a boot's flashing height be 8 inches (203 mm) minimum. However, NRCA is aware many pre-manufactured flashing boots generally do not meet this height recommendation.
Detail SPF-18(FB) from The NRCA Roofing and Waterproofing Manual, Fifth Edition
In the detail, the flashing boot is secured to the membrane, and the top edge is held in place with a drawband. Sealant should be applied between the plumbing vent and flashing boot. The flashing's top edge should be sealed with appropriate sealant and tooled to facilitate runoff. If required, sealant also should be applied around the perimeter of the boot's flange.
To ensure proper flashing installations at all penetrations, plumbing vent stacks and other pipes should have a minimum 12 inches (305 mm) of clearance on all sides from walls, curbs and other projections.
Joan P. Crowe is an NRCA manager of technical services.
COMMENTS
Be the first to comment. Please log in to leave a comment.