Tip of the Month
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 American do not have proper attic ventilation. Why? Because most people are unaware that attic ventilation
can impact the longevity of their entire home!
For example, in the summer, an improperly
ventilated attic can cause heat to build in excess of 160°F. This superheated air eventually penetrates the ceiling insulation
into the living area below.
Types of damage that can result include:
A properly ventilated attic
can help reduce the load on your air conditioner by moving superheated air out of your attic before it builds up and causes
- Premature aging of your roofing system (“fried” shingles)
- Warping, cracking, or breaking down of wood framing
- Damage to siding, exterior or interior paint, and wallpaper
- Higher energy costs
In the winter, various household appliances, bathtubs, showers, and cooking vapors can
contribute to excess moisture build-up. Improperly ventilated attics will allow this moisture to collect and cling to the
underside of the roof. There, it will condense and fall, soaking the attic insulation and reducing its efficiency.
Additional structural damage can include:
Proper Attic Ventilation
deck warping and rotting of the wood frame
- Mildew growth
- Buckling of shingles and felt
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
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., 1-1/2 feet of each), to ensure proper air flow through the attic. To calculate
the amount of ventilation you need for your home, follow the example below.
Calculating Your Ventilation Requirements
the number of lineal feet of Cobra® Exhaust Vent needed for a 30’x40’ 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
Intake ventilation MUST be at least equal to exhaust ventilation. To determine
the number of intake vents needed, select your vent and install enough vents so that their combined NFA is at least 288 square
Always have a balanced ventilation system. In no case should the
amount of exhaust ventilation exceed the amount of intake ventilation.
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
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 required seventeen (17) lineal feet of Cobra® Exhaust Vent to
meet FHA minimum requirements.