Soffit Vents – Installing Soffit Vents

Installing soffit vents, in concert with roof vents, helps to extend the life of roof shingles, and prevent ice dams and other moisture related damage that can occur in the attic.

It is important when determining and installing an attic vent system to make sure that there is at least an equal amount of ridge vent and soffit vent.

Installing Soffit Vents – How Much to Install?

Many builders recommended actually installing slightly more soffit vent than ridge vent, e.g. 60% soffit vent and 40% ridge vent.

To calculate the total amount attic ventilation necessary for a home, multiply the length times the width of the home’s foundation size and then divide by either 150 or 300. If the attic insulation has a faced surface and it facing towards the warm room of the home, divide by 300. If the attic insulation does not have a vapor barrier divide by 150.

Once you have calculated the total amount of attic ventilation required, divide this number by 2 to calculate the amount of square feet required for both the soffit vents and the ridge vents.

Note that if you plan to use cap vents in lieu of ridge vent you will need to double the amount of attic ventilation area required.

Once you have calculated the required number of square feet of both the soffit vents and ridge vents, you may need to convert these numbers to square inches. To do this, simply multiply the number by 144. (Note that there are 144 square inches per 1 square foot). After calculating the required soffit vent area in inches you can then divide this by the amount of net free area associated with the particular individual soffit vents you plan to use.

This calculation will tell you how many soffit vents you will need to install in your roof eaves. For example, if the total soffit square area requirements is 720 square inches, and if the particular soffit vents you plan on installing each have a net free area of 72 square inches you would need a total of 10 soffit vents.