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Damage from Poor Roof Ventilation

Proper roof ventilation is important for temperature and moisture control.

During the summer, excess heat that builds up in the attic during the day results in high energy costs for cooling. Also, moisture produced within the home may move into the attic if ceiling vapor barriers are not used. If this moisture is not exhausted from the attic it can condense and cause insulation and construction materials to deteriorate.

The American Institute of Architects estimates that 90 percent of homes in the U.S. have unacceptably high levels of moisture. Surely Canadian homes suffer from the same problem.

The Results of Inadequate Roof Ventilation Can be Serious

Here are some problems associated with an improperly ventilated attic space:

  • Your roof deck can warp or deteriorate and become spongy and dangerous to walk on.
  • The roof deck will not be allowed to breathe, leading to dry rot.
  • The adhesives used in the plywood can deteriorate because of condensation.
  • Water vapour will condense on anything metal inside the attic, causing the metal to rust and leading to more serious problems.
  • In colder climates, high inside humidity combined with low outside temperatures can cause frost to form on the bottom of the roof deck, potentially leading to dry rot.
  • Insulation can trap moisture which will reduce the R-value of the insulation. Studies have shown that a 10% increase reduces your insulation’s effectiveness by about 15%.
  • Excess moisture can create an environment for the growth of certain molds and mildew that can cause dry rot and health problems.
  • Cooling units will need to be serviced or replaced prematurely because of excessive use.
  • Ice dams are more likely to form on your roof, leading to leaks.
  • Most shingle warranties require a lot of ventilation—as much as one square foot of net free ventilation area for each 150 square feet of floor space to be vented.

Make Sure You Have an Experienced Roofer

Most older homes have insufficient attic ventilation. This needs to be remedied when installing a new roof. Adequate roof ventilation is a requirement of the Alberta Building Code and of most shingle manufacturers. Failure to install proper ventilation can void the shingle manufacturer’s warranty.

In some ways, roof ventilation is as much of an art as it is a science. A trusted and experienced roofer who has worked in your area for years may be a better judge for your particular roof than any research study.