www.mrca.org — Midwest Roofer 16 TECHNICAL & RESEARCH Create Adequate Rooftop Clearance Inadequate rooftop clearances are a recipe for disaster. When penetrations through the roof are too close together or too near a wall, or when rooftop units are packed too tightly together, it is challenging for even an experienced, highly skilled professional to flash them properly. The result is poor flashings that will not pass inspection for the desired warranty, leading to costly and time-consuming change orders and repairs to get the warranty and prevent leaks and other problems. Any penetration through the roof should be at least 12 “flashing inches” out from a parapet wall or roof edge, meaning there should be enough space between the penetration and the wall or roof edge to accommodate at least 12 inches of flashing. Similarly, penetrations through the roof should be spaced at least 12 flashing inches apart to allow proper flashing. Drains require additional room to accommodate their bell housings and clamping rings. All drains should be at least 24 flashing inches away from walls or roof penetrations and be spaced at least 24 inches apart. HVAC units also need their space. When designing a roof with three or four small units, placing them on metal curbs attached to the membrane is acceptable. The contractor will be able to flash them correctly. But when there is a larger cluster of units, using metal or plastic platforms to elevate them 3 or 4 inches above the rooftop is a far more functional option. The pads can simply be placed on top of the membrane, with no flashing required. “Hot Stacks” Require TLC Flashing “hot stacks” that exhaust heat generated by machines operating below requires special attention. These stacks have the potential to create surface temperatures above 150 F and must, therefore, be treated differently from other types of projections to protect the roof membrane from heat-related damage. The stacks must be spaced at least 12 flashing inches apart, at least 12 flashing inches from walls and roof edges, and at least 24 flashing inches from drains. No exceptions. Uncured flashing membrane and non-reinforced membrane may not be used as wrap flashing. The flashing membrane also must not be in direct contact with the stack. A metal sleeve with a larger diameter than the actual flue should be installed, creating an insulating air space to prevent overheating of the membrane. The detail is then made watertight by adding a storm collar that protects the air space from the elements. Wall and Curb Flashing Heights Designers also must allow for adequate flashing when setting elevations. The National Roofing Contractors Association (NRCA) recommends flashing heights of at least 8 inches above the finished roof membrane. In high-precipitation northern regions, 12 to 16 inches above the finished roof Continued from page 15
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