Why Does A Roof Need Ventilation?

Most people don't fully understand the role that roof ventilation plays in extending the lifetime of a roof, and underestimate its importance in preventing related problems.

The purpose of roof ventilation is to keep air circulating and to reduce moisture accumulation. According to the American Institute of Architects, approximately 90% of homes throughout the United States have moisture levels that are too high.

Effective ventilation:

  • Allows outside air to circulate through the attic
  • Keeps attic area dry and cool
  • Helps to prevent rotting and mildew to roof rafters and plywood roof decking
  • Prevents moisture build-up in attic insulation
  • Reduces heat build-up in the attic
  • Reduces attic moisture and condensation
  • Prevents build-up of ice dams in cold climates

All major manufacturers require proper roof ventilation as part of their warranty requirements.

Generally Accepted Roof Ventilation Requirements

If you do a lot of reading on this subject you'll find that: (1) the benefits of roof ventilation are undisputed, and (2) experts and industry associations will have different opinions about which types of ventilation are best. As a general rule, one square foot of vent area per 300 square feet of attic flor space is recommended. And where you live can make a difference -- adequate roof ventilation for a home in South Carolina might be different from that of a home in another part of the country.

Problems Caused by Inadequate Roof Ventilation

  • Achieving the right balance is important. Too much ventilation can be a problem because too many roof vents represent additional spots where leaks can occur. Too little ventilation causes moisture and humidity build-up during cold months, and puts a drag on air-conditioning and energy efficiency during hot months.
  • Poor ventilation causes moisture buil-up in the attic. Moisture turns into condensation and if left unchecked will eventually cause rot to rafters and roof decks. Excess moisture can also get trapped between underlayment and shingles, causing them to warp or buckle.