How Many Vents Does a Roof Need?
Many homeowners may underestimate the importance of adequate attic ventilation. The common misconception is that roof vents are to keep attic space from getting to hot in the summer. While this is true, their primary function is to let excess moisture and humidity escape from the home.
There has been a significant increase in the use of Energy Efficient building materials over the last 15 years. Energy efficient windows, siding, roofing, and insulation allow less natural airflow in and out of the home.
Moisture fills the air in our home from cooking, showering, and running appliances such as, dishwashers and clothes dryers. This warm humid air migrates upward and eventually into our attic space. If there is no place for this moisture to escape, it becomes trapped in your attic. This trapped hot and moist air can have a detrimental affect to the integrity and aesthetic appeal of your home. It could even decrease the life expectancy of certain building materials.
Absence or lack of proper attic ventilation forces this trapped moisture to permeate the roof decking and rafters. When the moisture content of wood in your attic reaches a certain level, rafters and decking begin to sag. As a result, you end up with a drooping or sagging look to your roof, which greatly impacts the appearance or “curb appeal” of the Home.
Inadequate attic ventilation can also decrease the life of asphalt composition shingles by as much as 50%. Good ventilation allows for cool air flow underneath the roof deck and cools the shingle. Shingle manufacturers will not warranted their products without the minimum required “Net Air Flow” for your attic size.
Net Air Flow is a formula used to calculate area of openings in square inches need for intake and exhaust vents to adequately ventilate a space based necessary cubic footage. A balanced system consists of soffit vents for cool air to enter and roof vents at the highest point of the roof for hot/moist air to exit. Wind Turbines or Attic Fans can increase the efficiency of your attic ventilation system, but require more soffit vents because they move more air than stationary roof vents.
I hope this was helpful. Many roofing contractors do not address attic ventilation because they either do not understand it or maybe they just were never informed of the importance or it. Great attic ventilation is often overlooked and misunderstood, but I truly feel that it plays a key role in maintaining the integrity and long-lasting beauty of your home.