Where Commercial Flat Roofs Actually Leak, and Why the Stain Is Rarely Under the Problem
Leaks on low-slope roofs start at details, not in the open field of the membrane: penetrations, wall and parapet flashings, seams, drains, and ponding areas. Water can travel 20 to 30 feet or more under the membrane before it surfaces inside, so the stain marks the exit, not the entry. Pittsburgh’s 35 freeze-thaw cycles a…