How Much Attic Venting Do I Need

Venting a homes attic is a very important best building practices will say 50 at the ridge and 50 at the soffits unobstructed.

How much attic venting do i need.

Venting plays a huge part in how your quietcool whole house fan system works to its full potential. The federal housing administration recommends 1 square foot of attic ventilation for every 150 square feet of attic space. Ideally there should also be plenty of soffit intake space their calculations recommend 336 net square inches of open soffit. We always recommend at least having 1 sqft of net free area venting for every 750 cfm in your system.

However with only two 1 ft x 2 ft gable roof vents i ll need an additional 7 sq ft of exhaust vents. Divide the attic s square footage by 150. Of total vent space needed. If the slope of your roof is greater than 6 12 you will need more ventilation to reflect the extra volume of attic space.

Calculate 20 per cent more for 7 12 to 10 12 pitches and 30 per cent more for a pitch that is 11 12 or greater. As a certified licensed home inspector it is not correct to say too much ventilation is bad for an attic unless rain moisture is getting in. This will give you the amount of net free venting in square feet required for the fan you select. Do not use mechanical means electric attic fans.

The answer is rafter venting. A 50 x 30 attic would have a total area of 1 500 sq. Calculate the total vent area needed. You can only bring in as much air as you can discharge out of your attic vents.

Length x width of attic in feet 150 total sq. Take the total cubic feet per minute of air flow cfm of the fan and divide by 750 2. According to the home ventilating institute hvi powered attic ventilators need to move a minimum of 700 cubic feet per minute cfm for 1 000 sq. You mention exhaust vents shouldn t exceed intake vents in the roof for proper circulation.

I need additional exhaust ventilation in my roof with the planned installation of a whole house fan in the attic of my home located in sf bay area. Ft of attic space for example 20 x 50 to be effective. Ft divided by 150 equals 10 sq. Proper attic ventilation consists of a balance between air intake at your eaves soffits or fascias and air exhaust at or near your roof ridge.

Rafter vents or insulation baffles install in any rafter space to create narrow gaps that direct fresh air from the soffit vents to the peak of the roof. Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space.