Attic ventilation is a key component of all shingle roofing systems. Proper attic ventilation extends the life of a roof and reduces problems, because it minimizes the temperature difference between the attic and the air outside.
PROPER ROOF VENTILATION SAVES MONEY BY REDUCING MONTHLY UTILITY BILLS AND BY EXTENDING THE AC UNIT’S LIFE
Proper ventilation will remove moisture as well as heat from the attic. Trapped moisture can raise energy costs and damage roof system components prematurely.
Condensation inside the attic can be caused by the use of washing machines, dish washers, bath tubs, showers, and tumble driers unless these items are properly ventilated through the roof. In some cases the condensation can be bad enough to be mistaken for a roof leak.
Problems commonly associated with an improperly ventilated attic space include:
- Sumps between rafters (deck deflection) can happen because a plywood roof deck can warp or become spongy and dangerous. This occurs because one side of the plywood decking needs be able to “breathe” by being exposed to circulating air. The adhesives used in the plywood can deteriorate because of condensation.
- Insulation can trap moisture in an attic, which will reduce the insulation’s R-value and create an environment for the propagation of molds, spores, and fungi, which will cause problems.
- AC units will need to be serviced or replaced prematurely because of excessive use.
To properly ventilate an attic, two types of vents are needed.
Intake vents, which are located at the down-slope edge of the roof (eaves) and allow fresh air into the attic
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 or Bernoulli Principle to ventilate the attic space.
Many homes only have exhaust vents working near the ridge-line, and no intake vents at the eaves.