Parapet walls add architectural appeal and safety to flat roofs, but they also create one of the most vulnerable areas for water infiltration. The junction where your roof meets the parapet wall requires careful flashing installation to keep water out. Unfortunately, this area is also where many roofs develop their first leaks. Any experienced roofing professional will tell you that understanding parapet wall flashing and its common failure points is crucial for maintaining a watertight building.
What is Parapet Wall Flashing?
Parapet wall flashing is a waterproof barrier installed where your flat roof surface meets the vertical wall. Think of it as a protective shield that directs water away from this vulnerable connection point. Proper flashing creates two angles: one that covers the roof surface and another that extends up the wall, forming an L-shape or two-piece system that prevents water from sneaking behind the roofing membrane.
Common Flashing Failure Points
Inadequate Height: One of the most frequent mistakes is installing flashing that doesn’t extend high enough up the parapet wall. Flashing should reach at least 8 inches above the roof surface, and higher in areas with heavy snow or rain. When flashing is too short, water can splash over it during storms and seep behind the membrane.
Poor Fastening: Flashing must be securely attached to both the roof deck and the wall. Loose flashing allows wind-driven rain to penetrate underneath. Over time, inadequate fastening lets the flashing pull away completely, leaving gaps where water rushes in.
Separation at Seams: Parapet walls have corners and joints where flashing pieces must connect. These seams are prime leak locations if not properly sealed and overlapped. Each piece should overlap the previous section by at least 6 inches, and all seams need appropriate sealant or welding depending on the material used.
Cracked or Dried Sealant: Many flashing systems rely on sealants to fill gaps and create watertight bonds. Unfortunately, sealants deteriorate over time due to UV exposure, temperature fluctuations, and building movement. Cracked or missing sealant is one of the easiest problems to spot and one of the most common causes of leaks.
Improper Drainage: Water should never pool against parapet walls. When drainage slopes incorrectly or drains become clogged, water sits against the flashing constantly. This prolonged exposure finds every tiny gap and accelerates deterioration of flashing materials.
Prevention and Maintenance
Regular inspections are your best defense against parapet flashing failures. Check these areas at least twice yearly, paying special attention after severe weather. Look for rust, loose sections, gaps, or any visible damage. Keep the area around parapet walls clean and free of debris. Standing water and accumulated dirt accelerate flashing breakdown.
Parapet wall flashing protects your entire building from water damage, but only when properly installed and maintained. Don’t wait for leaks to appear before taking action.
Schedule a professional parapet wall inspection at 118-35 Queens Blvd Forest Hills, NY 11375 (718) 414-6067 https://www.nycrenovators.com today to identify potential problems before they cause costly interior damage to your property.
