Attic Ventilation Air Flow

Intake exhaust airflow in a house attic square footage 2 square inches of exhaust and square inches of intake net free area nfa needed.

Attic ventilation air flow.

Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. 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. 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. To calculate the amount of ventilation you need for your home visit gaf s ventilation calculator now. Air flows in through the soffit vents and out through the roof vents. The insulation will resist heat transfer into the house.

Ventilation can be accomplished using various products and techniques. Ventilation manufacturers assign an nfa value to the non motorized vents they make. 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. Most building codes require a ratio of 1 150 ventilation space to attic floor space.

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. Grab a flashlight and inspect your attic during the winter. 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. That said air resistance and interference such as vent grates reduces the area of true ventilation.

The ice traps water behind it allowing the water to seep back under the shingles and leak through the roof. Nfa is the unobstructed area through which air can pass through a vent usually measured in square inches. Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed. A new roof is more than just shingles.

Air follows the path of least resistance. 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. For the best results place roof ventilation near the roof s peak and soffit vents in the eaves. In other words the entire vent opening doesn t count as vented space.