Protect your roof from premature deterioration by providing effective
Homeowner's Best Choice
- Vents your attic... Allows heat and condensation to escape at the most effective location--the ridge
- Looks Terrific... 100% shingle-over design is virtually invisible when installed.
- Superior Protection... Helps to prevent wood rot and extends the life of your exterior paint.
- Safeguards Possessions... Helps limit mildew growth caused by damp attic air.
- Energy Efficient... May even reduce your utility bills!
- Safer... Helps prevent problems with insects, birds, and animals in your attic.
- Peace Of Mind... Backed by a 40-year ltd warranty*
*See ltd. warranty (available from your distributor)
for complete coverage and restrictions
Proper attic ventilation is crucial for a long-lasting roofing system!
Poor Attic Ventilation Can Ruin Your Insulation,
Destroy Your Shingles, And Raise Your Energy Bills!
Why Take Risks?
It is estimated that 9 out of 10 homes in North America do not have proper attic ventilation. Why? Because most people are unaware that attic ventilation can impact the longevity of their entire home!
Proper Attic Ventilation
Proper attic ventilation systems allow a continuous flow of outside air through the attic (see illustration
at left), protecting the efficiency of the insulation and helping to lower temperatures in the living space.
It consists of a balance between air intake
(at your eaves or soffits) and air exhaust
(at or near your roof ridge).
The FHA (Federal Housing Administration) recommends a minimum of at least 1 square foot of attic ventilation (both intake and exhaust) for every 300 square feet of attic space. For example, if your attic is 900 square feet, you need a total of 3 square feet of ventilation. This amount is generally divided equally between intake and exhaust ventilation (i.e., 11/2 feet of each), to insure proper air flow through the attic. To calculate the amount of ventilation you need for your home, follow the example shown on the next page.
Calculating Your Ventilation Requirements
Example: Calculating the number of lineal feet of Cobra® Exhaust Vent needed for a 30’x 40’ attic:
Calculate attic square footage
How: Multiply length of attic (in feet) times width of attic (in feet)
30’ x 40’ = 1,200 square feet
Calculate NFA (Net Free Area) needed for this attic by using the “1 in 300” rule
How: Divide attic square footage by 300
1,200 sq. ft. ÷ 300 = 4 square feet of NFA needed
Convert square feet of NFA to square inches
How: Multiply square feet of NFA by 144
4 sq. ft. x 144 = 576 square inches of NFA needed
Split the amount of NFA needed equally between the intake and the exhaust
How: Divide square inches of NFA needed by 2
576 sq. in. ÷ 2 = 288 square inches of NFA needed equally for exhaust & intake
Calculate # of lineal feet of Cobra® Exhaust Vent needed
How: Divide the square inches of NFA needed at the ridge by the NFA of the Cobra® Exhaust Vent
(Cobra® Exhaust Vent has 16.9 sq. inches of NFA per lineal foot)
288 sq. in. ÷ 16.9 = 17 lineal feet
This attic requires seventeen (17) lineal feet of Cobra® Exhaust Vent to meet FHA minimum requirements.
Intake ventilation MUST be at least equal to exhaust ventilation. To determine the number of intake vents needed, select your vent on page 12, and install enough vents so that their combined NFA is at least 288 square inches.
Always have a balanced ventilation
system. In no case should the amount of exhaust ventilation exceed the amount of intake
Last Updated on Friday, 25 May 2007 13:03