- Intake vents low on the roof and exhaust vents near the peak;
- Intake vents blocked by attic floor insulation
- Vents installed but underlayment/sheathing not cut to allow airflow;
Adequate Attic Ventilation Formula (You'll be estimating this, no calculator necessary):
12 square inches of net free ventilation for each:
- With no low-perm (plastic) vapor barrier: 150 square feet of attic space
- With low-perm (plastic) vapor barrier: 300 square feet of attic space
Twelve square inches might be an opening of 3 inches by 4 inches.
“Net free” means that louvers or other devices that reduce the actual size of the opening must be subtracted from the total opening size to find the net free size.
Whole House Fans:
In colder climates, whole house fans should have an insulated cover that will reduce heat loss during the heating season.
Ventilation Of Vaulted Roof Structures
Roof structures over vaulted (cathedral) ceilings are ventilated using soffit and continuous ridge vents. Properly constructed, thermal insulation is installed in rafter bays in a manner that leaves a 2” space between the top of the insulation and the bottom of the sheathing. Air enters this space from the soffit vents, travels up the air channel and out the ridge vents. This system helps ventilate the underside of the sheathing and keep the roof cool, helping to prevent the development of ice dams in cold climates and reduce cooling costs in warm climates.