The primary cause of leakage in fire windows is the degradation or failure of the perimeter seals and gaskets. These components, typically made of elastomeric materials like rubber or silicone, are critical for creating an airtight and watertight barrier between the window frame and the surrounding wall structure. Over time, these gaskets are subjected to environmental stressors including prolonged exposure to ultraviolet radiation from sunlight, extreme temperature fluctuations, and oxidation. This exposure causes the material to lose its elasticity, becoming hard, brittle, and eventually cracking. Once the gaskets shrink or crack, they can no longer effectively repel water, allowing moisture to infiltrate the building envelope.
Another significant factor is physical damage or improper compression of the sealing materials. During installation, if the gaskets are not correctly positioned or if the window is improperly shimmed and fastened, the seal may not be uniformly compressed around the entire perimeter. This creates gaps and weak points where water can enter. Furthermore, accidental impact during building maintenance or from other activities can dent the frame or dislodge the weather-stripping, compromising the integrity of the seal. Even minor distortions in the frame can be enough to break the continuous seal.
The design and installation of the fire window system itself are also fundamental. A common point of failure is an inadequate interface between the fire window frame and the surrounding construction. If the rough opening is not prepared correctly or if the wrong type of sealant is used to fill the gap between the frame and the wall, it creates a direct path for water ingress. It is crucial to use high-quality, flexible sealants compatible with both the frame material and the wall substrate. Additionally, while the intumescent seal—a key fire-stopping component that expands when heated—is essential for fire resistance, it is not designed to be a primary weather seal. Relying on it for waterproofing is a misconception; its primary function is to block smoke and flames during a fire, not to provide long-term weatherproofing. Therefore, a failure in the dedicated weather seals will lead directly to leakage, regardless of the condition of the intumescent strips. Regular inspection and maintenance of these external seals are vital to prevent water damage and ensure the long-term performance of the fire window assembly.