Best Practices Attic Ventilation

Adapted paraphrased with permission from best practices guide to residential construction chapter on best roofing practices.

Best practices attic ventilation. The recommended ventilation ratio to provide for vented attic assemblies when an air barrier is present is the 1 300 ratio as specified by most building codes. 1 300 ventilation ratio recommended. Experts recommend using attic ventilation in hot climates as part of an overall strategy to reduce cooling loads. Additionally attic ventilation is a key ingredient in the defense against ice dams in snow and ice climates.

Center nails between rafters 18 in. This configuration also tends to evenly wash the entire underside of the roof surface with ventilation air. The average family of four generates 2 to 4 gallons of water vapor a day through activities such as cooking cleaning showering laundry and breathing. Cut the hole for roof vents.

Roof insulation thermal resistance at roof perimeter should be equal or greater to thermal resistance of exterior wall. Cut the shingles for roof vents. These vents allow outside air to enter the attic at the lowest point of the roof along the underside of the eave. Mark attic roof air vent locations.

Ventilation helps even more when used in combination with radiant barriers. Drive nails up through the sheathing and. From the roof s peak. The international residential code irc provision for attic ventilation requires a ratio of one square foot of net free open ventilation area for every 150 to 300 square feet of attic square footage.

Attic ventilation can help remove the water vapor safely. For both attics and cathedral ceilings roof ventilation works best when it is balanced between high and low to take advantage of natural convection figure 2 55 at left. If your home is fitted solely with small gable end vents or a ventilator high in the roof you might want to consider adding soffit vents to increase airflow.