Normally, heat rises but without proper ventilation in the attic, heat does not rise but migrates. Proper ventilation prevents moisture buildup from the heated air which, will quickly bring on other problems such as, bacterial buildup, mold growth, wood rot, popped shingles and ice dams in the
Without proper attic ventilation, air becomes stagnant and stationary air means excess heat is not removed or its accompanying humidity. Exchanging air with outside fresh cooler and dryer air is what prevents all those problems.
Once heat from a hot attic begins to migrate, the home will heat up very quickly. A hotter home means more AC, higher energy bills and more wear and tear on the AC unit. This is not the only issue because excess heat creates a lot of moisture buildup. Proper ventilation will eliminate or minimize moisture, prevent damage and provide a cooler home. In the winter months, the cool attic will collect rising heat from the interior of the home and this brings with it, moisture build up because as it rises, it is “shocked” by the cold air and condenses into liquid which, is a winter attics’ worst nightmare and if living in snow regions, the dreaded ice dams will form.
To create air flow, there are two primary applications used in the United States and these are exhaust vents and intake vents. Refer to the diagram to see air flow of a typical attic. Exhaust vents allow moist warm air to flow out through ridge or turbine vents and intake vents allow cooler and dryer outside air to flow into the attic through cable, under-eave, or rafter vents. Two of the most common myths about attic ventilation are: “more ventilation is better,” and ventilation is causing heat loss in the winter.
Determining the right balance of air flow is important to the health of the attic, roof, and home. The general rule is 1 sq foot of ventilation for every 300 sq ft of ceiling space. Heat loss in the winter is not the fault of proper attic ventilation but poor insulation. Beware, venting an attic is an extremely controversial subject. Generally, the goal is to create and maintain uniform air flow of cool air from the outside through the space and then out the exhausts carrying the hot moist air from within. If this is not in perfect balance, there will be “hot spots” which, negate all the potential benefits from your ventilation efforts. Think of it as creating the optimal cross-breeze. The bottom line to attic ventilation is to remove all that wet, hot and stagnant air from causing serious damage.
For a cool summer home and warm winter home, excellent roof ventilation AND insulation will keep the energy bills down, prolong the life of the roof and increase creature comfort in the home.