Flashing: Its Vital Role in Preventing Water Infiltration – Part I
By: Sean McPartland
The exterior components of a building, including its roof, walls, windows and doors, collectively form a protective envelope that shelters the interior of a building from the environment. Water is the element that poses the greatest threat. Failure to adequately protect a building from water infiltration will significantly increase maintenance costs and ultimately reduce the service life of the structure. A leaking roof or wall assembly can lead to structural damage, threaten personal safety, and result in costly and untimely repairs. NYC Building Code performance requirements for exterior walls and roof assemblies, Section 1403 and 1503 respectively, require building envelope professionals and owners to provide roof and exterior wall assemblies that are weather resistant. Proper roof and wall flashing installation and maintenance ensure compliance to these requirements for protecting buildings from the elements.
Roof flashing refers to the materials used to protect the roof assembly from water infiltration at the intersection of the roof and roof mounted structures and projections. Areas where a roof penetration or structure creates a joint in the roof system are the most vulnerable. These include: parapets, chimneys, bulkheads, vent pipes, drains, towers, etc. The more of these locations, the greater the potential for serious leaks. Water infiltration in these areas if often caused by expansion and contraction of the building during temperature changes.
Wall flashing, working in conjunction with other components of the wall assembly, refers to materials that are used to prevent moisture from infiltrating the wall assembly and entering the interior of a building. Building corners, windows, doors, vent pipes, mortar joints, the tops of parapet walls, cracks or any other penetrations, fenestrations or material transitions create joints in the wall assembly that are susceptible to water infiltration. Additionally, masonry units are commonly composed of porous materials including, brick, cast stone, and similar products. The primary function of wall flashing is to either prevent water from entering the wall assembly, or to divert water that has entered back to the exterior.
There are many different flashing products available, and proper selection of flashing material is critical to the overall performance of the flashing system. Materials must be durable, waterproof and compatible with the adjoining masonry. Quality design and workmanship are as equally important as using the appropriate materials. Building envelope consultants and contractors must be experienced and familiar with installation techniques, manufacturer recommendations and product limitations. Lastly, to ensure the effectiveness of waterproofing systems, and to protect a building’s wall and roof assemblies, maintenance repairs should be performed in a timely manner.