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Showers Inside and Out: Diagnosing Roof Leakage


Roof leakage in residential and commercial buildings is a common occurrence in the spring as the snow is melting and rain is pouring. Water ingress can occur as a result of a variety of factors. Understanding the most common causes of roof leakage can assist in diagnosis so that liability can be appropriately assessed.
Common causes of roof leakage:

1. Old Age – Typical design life expectancy of roofing materials, including asphalt shingles and wood shakes, is fifteen to twenty years with proper maintenance. If a leaky roof has surpassed its expected lifespan, the leakage is likely a result of old age.

2. Severe weather conditions – Weather damage to a roof during a hail storm or strong winds can lead to leakage. However, roof materials are designed to handle most of the major beatings from Mother Nature. Standard application of Canadian asphalt shingles products should be able to resist a wind speed, including gusts, of 97 km/hr, which is based on American Society on testing Materials (ASTM) D3 161. If the roof is damaged by light winds other factors, such as age and construction methods, should be considered.

3. Ice damming – Ice damming occurs in the winter when warm attic air melts the snow on the roof. The melted snow will travel along the roof surface until it reaches a cold surface, such as an eavestrough or metal flashing, where the water will subsequently freeze. The freezing and thawing of snow and ice associated with ice damming can cause roof damage, including the lifting and deterioration of asphalt shingles. If a relatively new and well constructed roof leaks, the leaky roof is likely a result of a roof damaged from ice damming. Signs of ice damming include water stains on the soffit and ice and/or icicles on exterior cladding.

Keep an eye out for these conditions that can lead to ice damming:

  • inadequate insulation and ventilation inside the attic
  • poorly sealed ceiling vents, chimney, or attic hatch
  • poorly insulated duct work inside the attic

4. Construction deficiencies – The most common cause of residential roof leaking is improper placement or lack of roof flashing. Roof flashing consists of a piece of sheet metal – usually aluminum or galvanized steel – which is placed over joints in roof and wall protection to prevent water seeping into the house and causing damage. Areas on a roof where flashing is required include chimney locations and plumbing vents.

Moisture ingress through roof leaks can cause damage to the structure and can result in mold growth. It is critical to pinpoint the location of moisture ingress and stop the water from entering the building. Once the location and cause have been identified, it is best to consult a structural engineer to determine if any structural damage has occurred and advise on the reparation.


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