The Importance Of Proper Ventilation 

Without proper ventilation, heat and moisture can raise energy costs, create ice dams (See BLOG: Ice Dams & Dry Rot and the importance of proper ventilation) damage the roof system, as well as could jeopardize the structural components of your attic and roof.  The heat that rises from your house (mostly from showers, washing machines, dishwashers, and other large appliances) can raise the attic temperature to +60° C. This will create a considerable amount of condensation, in some cases, to the point that it is bad enough to be mistaken for a roof leak.

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

• The boards between rafters can begin to sink (deck deflection). The plywood decking can deteriorate or warp and become structurally weak and dangerous to walk on. This is a result of the plywood not being able to “breathe” properly due to the lack of circulating air. This is how condensation creates Dry Rot occurs.
• Water vapor will condense first on anything metal inside the attic; this will eventually cause the metal to rust. Heads can rust off nails, metal plumbing straps or straps holding HVAC ducting can rust in two causing the ducting to crash down on top of the ceiling joists or through a suspended ceiling. This problem is more common in humid climates.
• In colder climates – generally where the average January temperature is 32° F (0° C) or colder – high inside humidity (40% or greater) combined with low outside temperatures can cause frost to form on the bottom of the roof deck.
• Insulation can trap moisture which will reduce the R-value of the insulation and create a nice environment for the propagation of certain molds, spores, and fungi which will also cause problems.
• There is also the problem of mildew which is both damaging and can cause health problems.
• The roof system itself will deteriorate prematurely.

There are many types of attic vents available today. There are static vents, power vents, ridge vents, turbine vents, soffit/cornice vents, gable vents, starter vents, and cupola vents. These all come in a wide variety of sizes, styles and shapes. Some will ventilate better than others depending on the roof configuration, attic size, climate, etc.

To properly ventilate an attic, two types of vents are needed. Intake vents, which are located at the down-slope edge of the roof (a.k.a. eaves) and allow fresh air into the attic; and exhaust vents, which are located near or on the ridge line of the roof and allow air to leave the attic. The use of an exhaust vent in conjunction with an intake vent uses the natural forces of wind pressure and thermal effect, collectively known as the Stack Effect, to ventilate the attic space.