Flashing: General Information
Flashing is a critical, yet often overlooked, element of the roofing system and is a major player in protection from the elements. Quality roof installations include proper flashing and terminations for the best possible protection against leaks.
Flashing seals joints from water. Joints occur at areas on the roof such as parapets, stacks, curbs, and vents. These are vulnerable areas because they penetrate the actual roof – meaning there is an opening in the roof for that structure. Flashing is used to cover these areas to reduce the risk of water entering the roofing system, damaging the insulation, roofing deck, or building and contents below. Flashing needs to be watertight, yet still allow for the natural expansion and contraction of the roof in response to temperature changes. Flashing often works with gravity to direct water away from the penetration. This means that in order to enter the roofing system through a joint, the water must somehow work its way up the penetration.
Flashing is composed of two parts – base flashing and counter flashing (or cap flashing). Base flashing attaches to the roof itself. Counter flashing attaches to the penetration itself, overlapping the base flashing. Metal flashing, which is frequently used by most roofers, deteriorates over time as it is exposed to rain, wind, sunlight, snow, and ice. In the Southeast, it may be exposed to all of these elements during the same week. This leads to significant stress to the metal as it expands and contracts with the temperatures and the underlying building materials. Many roofers also use a black roofing compound around the penetration. This deforms easily as temperatures change. Cracking and separation may also be seen.
Experts recommend flashing structures with materials compatible with the roofing system. Quality roofing installations, such as those performed by LaFerney Commercial Roofing, use special sleeves for vent stacks and other like penetrations which are made of compatible materials with the roofing system. This provides a more secure fit and additional protection against leaks. Many installations use a black roofing compound around the penetration, which deforms easily as temperatures change. LaFerney Commercial Roofing frequently uses pre-fabricated PVC flashing skirts, made to the exact dimensions of each component. These flashings are manufactured and sealed under ideal, controlled factory settings for optimal water-tightness. The PVC flashing exactly matches the PVC roofing membrane, for maximum compatibility.
The majority of roof leaks occur at a penetration on the roof, making flashing failures one of the leading causes of roof deterioration. Penetrations should be carefully inspected for signs of damage of both the flashing material and the fasteners. Should signs of damage appear, repairs should be made promptly by a qualified repairman using compatible materials. Most repairs attempted on low slope or flat roofs are reverse flashed - directing water toward the roof opening rather than away from the penetration. See the photos below.
Roofing compound is a frequently used element to repair flashing. This is not a long-term repair solution and should never be used on a PVC roof. This compound becomes brittle and looses flexibility quickly – often within one year of application. Cracking occurs and any benefit from the compound is lost. In some cases, the chemical interaction between this compound and metal accelerates corrosion and deterioration of the roof.
Quick temporary patches in aluminum flashing can be made. Several commercial sealing products are sold for patching metal gutters – like gutter tape. A temporary patch may also be made from a piece of sheet metal held in place with flashing cement. NOTE: Not all metals are waterproof or weather proof. Care should be used to select the proper metal for the repair. Be certain to clean the area to be patched thoroughly. This is important for proper adhesion. A wire brush or steel wool is recommended. Cut the sheet metal to be used for the patch so that it will overlap the hole by at least three inches on each side. Apply roofing cement and press the patch into place. Use firm pressure, but not so much that the cement oozes onto the roof. This patch is strictly temporary.