It is estimated that nine out of ten homes in North America do not have adequate ventilation. Most people don’t understand the long term effects this can have on their entire home. Proper attic ventilation is very important to avoid moisture buildup and aid in temperature control.
In the winter, warm air from your living area, bathroom vents, cooking vapors, and other home appliances can contribute to excess moisture build-up. Without proper ventilation, this moisture will collect on the underside of the roof. The moisture will fall and soak the insulation, reducing its efficiency.
Some other types of damage that can result from an improperly ventilated attic are listed below:
1. Premature aging of your roofing system caused by extremely hot air baking the underside of the roof.
2. Depressions in the roof sheathing between rafters caused by moisture on the bottom side of the plywood.
3. Damage to the siding, paint, and wallpaper
4. Higher energy costs resulting from warm or cold air exchanging between the attic and the living space below.
5. Ice dams caused by warm air in the attic space melting the bottom layer of snow on the roof and refreezing at the gutter. This buildup of ice traps additional melting snow causing it to pressurize and back up under the roofing system and into your home. This can cause extensive damage to your ceilings and walls.
6. Mildew and mold growth.
7. Buckling or curling shingles and felt.
Proper attic ventilation allows constant fresh air to flow into the attic space. This consists of a balance between air intake at your eaves or soffits and air exhaust at or near the roof’s ridge.
The Federal Housing Administration (FHA) recommends a minimum of at least 1 square foot of attic ventilation, both intake and exhaust, for every 300 square feet of attic floor space.
Calculating Your Ventilation Requirements – Example
Step 1- Calculate attic square footage
How: Multiply length x width of attic (in feet)
30’ x 40’ = 1,200 square feet
Step 2- Calculate the Net Free Area (NFA) using the “1 in 300” rule
How: Divide the attic square footage by 300
1,200 sq. ft. ÷ 300 = 4 square feet of attic ventilation
Step 3- 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
Step 4- 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 and intake
Most ventilation products are broken down into square inches. This means that if you are using a soffit vent that provides 56 square inches of NFA per vent. You would divide 288 ÷ 56 = 5.14 soffit vents total. If your ridge vent provides 18 sq. in. of NFA per linear foot, then 288 ÷ 18 = 16 ft. of ridge vent needed. Now, there’s a bit of fun math for you.
Aside from having proper ventilation, it is also a good idea to make sure your attic has sufficient insulation. This will keep hot attic air from penetrating through the ceilings or vice versa. Having sufficient ventilation and attic insulation are key components in keeping your house warm in the winter and cool in the summer. When thinking about replacing your roof, it is important to make sure any ventilation issues are addressed and corrected in order to eliminate any future problems.
Please leave any questions or comments below or if you would like to speak to a professional from our company about any of your roofing or ventilation needs, please call us today at 866-365-5056.