b'TECHNICAL & RESEARCH Continued from page 15Create Adequate Rooftop Clearance Hot Stacks Require TLCInadequate rooftop clearances are a recipe for disaster.Flashing hot stacks that exhaust heat generated by When penetrations through the roof are too closemachines operating below requires special attention. together or too near a wall, or when rooftop units areThese stacks have the potential to create surface packed too tightly together, it is challenging for even antemperatures above 150 F and must, therefore, be experienced, highly skilled professional to flash themtreated differently from other types of projections to properly. The result is poor flashings that will not passprotect the roof membrane from heat-related damage. inspection for the desired warranty, leading to costly andThe stacks must be spaced at least 12 flashing inches time-consuming change orders and repairs to get theapart, at least 12 flashing inches from walls and roof warranty and prevent leaks and other problems. edges, and at least 24 flashing inches from drains. No Any penetration through the roof should be at least 12exceptions. flashing inches out from a parapet wall or roof edge,Uncured flashing membrane and non-reinforced meaning there should be enough space between themembrane may not be used as wrap flashing.penetration and the wall or roof edge to accommodate at least 12 inches of flashing. The flashing membrane also must not be in direct Similarly, penetrations through the roof should becontact with the stack. A metal sleeve with a larger spaced at least 12 flashing inches apart to allow properdiameter than the actual flue should be installed, flashing. creating an insulating air space to prevent overheating of the membrane. The detail is then made watertight by Drains require additional room to accommodate theiradding a storm collar that protects the air space from bell housings and clamping rings. All drains shouldthe elements.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.Wall and Curb Flashing HeightsDesigners 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 16 www.mrca.orgMidwest Roofer'