Attic Ventilation

Attic ventilation serves two important purposes. First, attic ventilation removes moisture that may find its way into the attic from the living space through small ceiling entrances (i.e., through gaps around plumbing stacks, bathroom fans and attic hatches). Second, attic ventilation removes heat that can reduce the life of your homeʼs shingles.

Attic ventilation is separate from ventilation for the living space of the house provided by fans such as a bathroom exhaust fans. Generally speaking, natural airflow attic ventilation methods are used (passive airflow). With this method, air flows into the roof space through perforated soffits located by your homeʼs eaves and exits through passive (non- powered) vents located near the peak of the roof.

The distribution and number of attic vents in your home will have been built according to the Building Code. There are a number of different types and methods of attic ventilation, including the following:

  1. A flat metal or plastic vent located on the roof near the peak;
  2. A round vent with a rotating top section;
  3. A ridge vent of continuous stripping located along the peak or ridge of the roof;
  4. A gable end vent on the enclosed attic wall located at the end of the trusses.

Passive roof vents perform their function in all seasons and are generally maintenance-free; however, they should never be blocked during the winter season. In homes with complex roof designs and numerous attic spaces a powered fan unit may be used as part of the ventilation system. These fan units will require occasional motor maintenance.

Truss Movement

Homes built since the 1970s are not typically built with attic rafters and joists, but trusses. The ceiling of your home is attached to the lower chords of these wooden trusses, which tend to shrink and expand seasonally when temperatures and humidity changes. Crown mouldings are often installed along the ceiling and the top of the walls to minimize the visibility of any gaps between the ceiling and the walls that may appear when truss movement occurs.

Did you Know?

Similar to truss movements, thermal bowing (another type of seasonal wall movement) may also occur in your home. You may notice thermal bowing in your home along your kitchenʼs backsplash if the wall is also an exterior wall for your home that experiences seasonal temperature changes. Another common area where thermal bowing occurs is along stair stringers placed along an outside wall.

During colder months, you may notice the effects of these truss movements when a slight gap appears between the interior walls of your home and the ceilings. As the trusses expand and contract, the ceiling can lift slightly off of the walls of your home. The ceiling will then drop back into place during warmer summer months. One method for handling this is to use or install decorative crown mouldings to minimize the cosmetic effect of seasonal truss movements. This is normal.

Leaks Due to Snow or Rain

Under unusually high wind conditions, even properly installed roof vents may not be able to stop some moisture from entering the attic space. In most situations, this moisture will evaporate without any staining or leaking into the interior of the home. If leakage or staining is noticed, the location of the roof vent may need to be altered or moved.

For more information or to find a reputable service providers in your area, visit the Canadian Home Buildersʼ Association – Saskatchewan website and Membership Directory at