Attic Ventilation Air Flow

Air follows the path of least resistance.

Attic ventilation air flow.

Air flows in through the soffit vents and out through the roof vents. Intake exhaust airflow in a house attic square footage 2 square inches of exhaust and square inches of intake net free area nfa needed. Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation. Grab a flashlight and inspect your attic during the winter.

Ventilation can be accomplished using various products and techniques. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. Nfa is the unobstructed area through which air can pass through a vent usually measured in square inches. These ice dams form when warm attic air melts the snow on the roof and the water refreezes along the colder edge of the roof.

In the summer natural air flow in a well vented attic moves super heated air out of the attic protecting roof shingles and removing moisture. Proper attic ventilation can help reduce the load on your air conditioner. Most building codes require a ratio of 1 150 ventilation space to attic floor space. In a properly designed and installed attic ventilation system that means the air will flow from the intake vents to the exhaust vents flushing out the warm moist air along the entire underside of the roof deck.

The ice traps water behind it allowing the water to seep back under the shingles and leak through the roof. Intake vents located at the lowest part of the roof under the eaves allow cool. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents.

A new roof is more than just shingles. Effective attic ventilation systems reduce damaging heat and moisture in your attic promote energy efficiency by helping to reduce the load on your air conditioner in the summer and also reduce the risk of ice dam formation on your roof. If you see dampness or frost you need better roof ventilation and some attic vents. That said air resistance and interference such as vent grates reduces the area of true ventilation.

Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed. In other words the entire vent opening doesn t count as vented space. Ventilation manufacturers assign an nfa value to the non motorized vents they make. To calculate the amount of ventilation you need for your home visit gaf s ventilation calculator now.