Ratio Of Soffit Vents To Roof Vents

Attic ventilation soffit intake to ridge outlet air flow or square inches ratio.

Ratio of soffit vents to roof vents.

One square foot equals 144 square inches so the standard 16 inch by 8 inch soffit vent is 0 89 square feet. Roof vent soffit vent ratio what posted in general discussion on september 27 2000 07 49am a prospective customer has a roof with approx 448 sq. Net free area table net free attic vent area type of vent sq. An important part of installing any system of ventilation into your roof system is to make sure that there is a point of entry and a point of exit for airflow.

Pick out your soffit vent size and determine the square footage of the vent. Approximate high vents exhaust filtervent 8 length 144 shinglevent ii 4 length 72 roof louver 50 wind turbine 12 112 rectangular gable louvers. Enter square footage calculate or enter the square footage of the attic or area to be vented. Adding under roof ventilation is usually a great idea but if the relative sizes of the intake and outlet vents are not proper the building will suffer increased heat loss and thus an unnecessarily high home heating bill.

Click to enlarge any image. And while both a roof vent and an overhang vent perform this task there is one big difference. 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. For example if you use 16 inch by 8 inch soffit vents each vent is 128 square inches.

However natural air flow from the outside will bring the moist air back into the attic through the soffit vents kind of like a vacuum. As the warm moist air leaves the bathroom through a soffit it leaves in a downward motion. To find the number of intake vents required use the net free area table below see low vents intake. When these areas need airflow however to help ventilate the home and keep air circulating throughout your attic you need more than a simple soffit made of solid wood or vinyl.

The above formulas will give the amount of cor a vent ridge vent needed for a 1 150 vent ratio provided an equal or greater amount of soffit venting is used. For a 1 300 ratio building code minimum use half the amount of ridge vent. The soffit is one of the most overlooked parts of your home s façade. Divide this by 144 to calculate how many square feet each vent is.

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. Inches of roof vent 7 slant back roof vents he has approx 5 184 sq inches of soffit vent that looks like approx 11 times as much intake capacity as output will such an arrangement likely cause a reverse venting situation. You need a ventilated.