Attic Ventilation

Proper attic ventilation is one of the biggest factors in increasing the energy efficiency of your home. (The other is insulation.)

What it is

Attic ventilation allows air to flow through your attic space and back outside. In the summer it reduces heat build up in the attic which can damage shingles and increase your air conditioning bill. In the winter it keeps the roof surface cool which helps prevent ice dams from forming.  It also reduces moisture build up which causes mold and rot.

How it works

A proper attic ventilation system is composed of intake and exhaust vents.

  • Intake vents: best positioned at the eaves or soffits (near the edge of the roof), allow outside air to enter the attic.
  • Exhaust vents: best positioned at the peak of the roof or along the ridge, allow hot and moist air to escape from the attic.
Important Notes:
  • If insulation is covering your intake vents than the system is rendered ineffective.
  • Having an attic fan that is too powerful for the attic space will suck conditioned air from the living space below and raise your energy bills.
  • Having your HVAC unit and duct work installed in the attic often wastes close to 20% of the air used to heat/cool the home and often causes excessive moisture in the attic space. To reduce the impact on your energy bills and the attic ensure that the duct work is well sealed and insulated.
  • When having roof, siding, or insulation work done ensure that your contractor has a plan for proper attic ventilation

Vent Requirements

According to most building codes, you need one square foot of vent area for each 150 square feet of attic floor space. The minimum is one square foot for every 300 square feet of attic floor space if there is a vapor retarder or the space is balanced between the ridge and intake vents.

A balanced ventilation system means about 50 percent of the required ventilating area should be provided by exhaust vents in the upper portion of your attic with the remaining 50 percent provided by intake vents.

Please remember, building codes specify the minimum amount of ventilation. You may want to increase the requirement to ensure proper ventilation.

Common Mistakes

Too many times, homeowners install products that short-circuit their ventilation system. When designing a ventilation system, avoid these common pitfalls:

  • Using a combination of different types of exhaust vents, like power vents with ridge vents. In this case, competing vents pull air from each other instead of from pulling from the intake vents.
  • Underestimating your ventilation needs. Remember that 15 roof louvers or 5 turbine vents would be needed to provide the same ventilation as 42 feet of ridge vent on the same house.
  • Installing exhaust vents without adequate intake. An effective balance of intake and exhaust must be achieved to properly ventilate your home. The flow of air in your attic is limited to the amount of intake.
  • Installing a ridge vent that doesn’t have an external baffle to increase air flow and protect from weather infiltration.