Attic Ventilation



Roof, Soffit, and Gable Vents - more info

Attic Exhaust Fans - more info

In the old days, attic ventilation was not important.


Houses had very little insulation and were not very air tight. Now, homes are well insulated and tightly sealed. Attic ventilation is needed for a comfortable home. Building codes now usually require 1 square foot of ventilation for every 300 square feet of attic area, divided equally between intake and exhaust vents. This is simple arithmetic, no guesswork is involved

In Summer

Without attic ventilation, summertime attic temperatures can exceed 160 F. Even at night the attic stays hot. The excessive heat reduces the life of your roof and eventually penetrates to the living space of your home. A well ventilated attic will make your home noticeably cooler and reduce the load on your air conditioning.


In Winter



Attic ventilation removes moisture from your attic. Moisture in your attic can cause mold and mildew. Attic ventilation can also help prevent ice dams.
Water vapor is produced from bathing, cooking and household appliances. This moist air rises through the attic until it contacts the cold winter air, where it can condense into water droplets on the underside of the roof. It then can drip onto the insulation, reducing its efficiency. The water can cause mildew and mold, rot the wood, damage and spot ceilings and paint, and cause damage to the roofing. Also, ventilation helps prevent ice dams, which is especially important in Colorado. Ice and snow on a roof will melt and run down the roof to the cooler eaves, where it can freeze and create a dam, trapping moisture on the roof. Ventilation helps to prevent this by keeping the roof deck temperature consistent.


How much attic ventilation do I have?



  Type of vent # of vents multiply by si nfa
of vent

= Total si nfa
  RV51 or box vent ________ multiply by 51 = _________
Large dome or unused
attic exhaust fan
________ multiply by 144 = _________
turbine - 14" ________ multiply by 110 = _________
ridgevent ____ linear feet multiply by 18 si/ft = _________
Gable vent 12" x 12" ________ multiply by 60 = _________
Gable vent 12" x 18" ________ multiply by 90 = _________
Soffit vent 4" x 16" ________ multiply by 26 = _________
Soffit vent 6" x 16" ________ multiply by 45 = _________
Soffit vent 8" x 16" ________ multiply by 65 = _________
Total vent area = _________




Vents are rated in square inches (si) of net free area (nfa).
Net free area is the amount of actual free space, allowing for the screens and louvers.
To convert square feet to square inches, multiply the square feet by 144 (number of square inches in one square foot).

To download this as an Excel spreadsheet (with photos) CLICK HERE.



Call for a free estimate.
303-233-1025