Roof Flashing: What is it?

Many homes and commercial building owners have asked the question “what is roof flashing?” when discussing proposals they have received for repairs or roof replacement.

The term roof flashing can be easily summarized as a form of protective covering, that is used at termination points, transition areas, or protrusions through a roof.

As a result; there are different types and styles of roof flashings, designed for application at specific roof areas.

Some of the most common roof flashings are described below, but first to understand; is that roof related flashings essentially fall into two material categories. One type of flashing is comprised of the materials used for water-proofing the field of the roof area.

Such an example would be a flat roof that is covered using modified bitumen membrane sheets. Where that roof structure joins a wall; pieces of modified bitumen membrane would be used to reinforce the transition between the wall and roof; effectively “double sealing” this vulnerable area from potential water ingress.

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The second category of material used for roof flashing is metal. Commonly used today, pre-painted galvanized steel is a preferred choice for metal roof flashings. They can also be fabricated from copper, leaded copper, zinc, or galvalume metals.

For roofing requirements, 26  gauge sheet metal is the accepted standard. “Gauge” of the metal, refers to the thickness of the metal. Where galvanized steel is concerned; the lower the number, the thicker the metal sheet is. As an example; 24 gauge metal would be thicker than 26 gauge metal. The opposite is true when discussing the thickness of aluminum materials.

Metal flashings which are used at the perimeter of flat roof areas, and are referred to as cap flashing, cant flashing, and coping metal; are specific profiles of metal which relate to the finished roof edge design.

All metal roof flashings are fabricated using a metal brake, to create the specific profiles required, which are calculated from field measurements. Such work is completed by sheet metal mechanics and tinsmiths.

Other examples of metal flashing profiles include wall flashings, ledges, door sills, curbs, chimneys, and skylights. Such details can be found on both flat roofs and sloped roof assemblies.

Metal roof flashings are specifically designed to protect the membrane roof flashings used as waterproofing or water-shedding reinforcement for the roof assembly. They further serve to provide a neat and finished appearance for the roof assembly.

Properly fabricated; metal flashings designed for flat roofing application, are designed to have slip-locks between the adjoining metal pieces. This allows for the expansion and contraction of the metal resulting from weather changes and building movement. Specifically;  the term is referred to as thermal expansion and contraction.

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Additional metal flashing installation requirements include joining the metal at corner joints using “locked” or “locked, standing” seams. This method, involves crimping adjoining pieces of metal located on opposing angles and corners.

Other methods of securing metal roof flashings can involve soldering metal sections together. This method is often used when copper sheeting is used. Copper is joined using lead solder or brass rod. Considerable expertise is required for completing such work.

A key to a successful soldered joint will involve thoroughly cleaning the metal surfaces to remove any residue or contaminants. This allows the soldered seam to hold and prevents splitting over time and temperature change.  Copper is a superior metal for longevity, as it can last in excess of 50 years.

Roof flashings can also take the form of pre-manufactured items, which are designed for a specific purpose, such as covering a plumber’s vent protruding through the roof assembly. Such pre-manufactured flashing products can be either like-kind to the roofing membrane, or metal.

It is important to note that roof related flashings are a key component required for the watertight integrity of any roof system. When a roof is being replaced; it is always best to replace such components because re-use of older materials can lead to premature failures, and are a common source of leaks in younger roof assemblies.

Roof related flashing details are a leading cause of roof leaks if they are not completed in a diligent and professional manner, or if they fail over time. Roof flashings can be repaired, and when done properly will extend the overall life-cycle of a roof assembly.

Home and building owners should be careful to evaluate the type and methods of flashing detail work when comparing bids from competing roofing contractors. As more material and labour is required to complete a competent job. By lessening a specification, or omitting the replacement of some flashing items it can serve to reduce the price of a particular bid. While many home and building owners focus on the price of the job, they can mistakenly, or through lack of knowledge, omit evaluation of these critical workmanship points.

The old adage is true; “you really get what you pay for”.

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