Long term function of metal flashings on a Calgary roof installation


Metal flashings on your Calgary roof

No matter the product installed on your Calgary roof installation – asphalt, cedar, slate, steel, limestone – all of these products use galvanized flashing.  Where the roof meets walls, skylights, & chimneys there is galvanized Step Flashing or Wall Flashing.  Where two panels of a roof meet there is galvanized Valley flashing.  This metal has a functional life expectancy that is affected by various factors on the roof.

What is “galvanized” metal?

  Iron or stainless steel left exposed to the elements will oxodize and will no longer be able to shed water.  Zinc is applied during the process of galvanization as a protective coating to prevent rust.  Hot-dip galvanization is the process of submerging the base metal in molten zinc, and protects in two ways:

  • It forms an air and water tight coating that prevents other materials interacting with the base metal  – the iron or steel
  • If the protective zinc coating becomes scratched or penetrated, the zinc will act as an anode and will oxidize in place of the base metal.

At a certain point the protective capabilities of the zinc are exhausted and the steel begins to corrode, and shortly thereafter will begin to leak.  This typically takes 20+ years to occur, and often times some of the flashing will see several roof installations before needing replaced.

Rotten metal flashings on a Calgary roof installation

The steel on these critical roofing flashings has begun to deteriorate

Some metal flashings are more easily replaced that others.  In places where valley metal, metal around skylights, or where counter flashings has been used – all of these allow for replacement of the metal with the roof, and indeed we strongly urge replacement during our work.  Step flashing that runs behind stucco or vinyl siding is difficult (time consuming) to replace, and metal that interacts with old chimney sometimes has the same problem.

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