What is net free venting area?

When discussing ventilation, the term “Net Free Area” or NFA is used to describe the amount of space available in any type of vent that can be used to freely pass airflow. This is essentially the empty spaces you see in the installed screens and louvers on most passive vents.

What are two common ways to ventilate the attic space?

There are two methods used to ventilate attics: static and mechanical. The most common method is the static method.

How do you calculate net free area of a vent?

To calculate NFA, take the attic square footage ÷ 2 = square inches of exhaust and square inches of intake NFA needed.

What are soffit vents?

These vents allow outside air to enter the attic at the lowest point of the roof—along the underside of the eave. They’re most effective when used in conjunction with a continuous ridge vent. Soffit vents come in several sizes and styles, including small round discs and rectangular grilles.

What should the net free area be for an attic vent?

The Passive Vent Net Free Area table gives the net free area ventilation for some common roof and gable passive vents. Should you need to add more air intake ventilation to your attic, simply determine the number of vents needed from the table based on your net free area requirements.

How is the net free area of a passive vent determined?

The amount of net free area available from any given passive vent depends on the type of vent used and the size of its screen, vent holes, or louvers.

How to calculate the net free ventilating area?

Venting Calculations To determine the net free ventilating area of a vent, divide the gross ventilating (do not include metal frame edges) area by the Area Factorbelow. Covering Area Factor Bird blocks per hole factor

What kind of mesh screen do I need for my vent?

With a 4 mesh weave, you’ll prevent mice and other rodents from entering through your vents. With an 8 mesh weave, you’ll be able to stop bees, larger insects, and flying embers from getting into your home. Surface finish coatings include standard mill finish and black or green polyester coating.