Attic Ventilation Air Flow

Grab a flashlight and inspect your attic during the winter.

Attic ventilation air flow.

Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. 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. Air follows the path of least resistance.

Ventilation can be accomplished using various products and techniques. The ice traps water behind it allowing the water to seep back under the shingles and leak through the roof. Most building codes require a ratio of 1 150 ventilation space to attic floor space. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents.

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. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. The insulation will resist heat transfer into the house. 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.

If you see dampness or frost you need better roof ventilation and some attic vents. Nfa is the unobstructed area through which air can pass through a vent usually measured in square inches. Ventilation manufacturers assign an nfa value to the non motorized vents they make. For the best results place roof ventilation near the roof s peak and soffit vents in the eaves.

Proper attic ventilation can help reduce the load on your air conditioner. A new roof is more than just shingles. To calculate the amount of ventilation you need for your home visit gaf s ventilation calculator now. That said air resistance and interference such as vent grates reduces the area of true ventilation.

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. In other words the entire vent opening doesn t count as vented space. Intake vents located at the lowest part of the roof under the eaves allow cool. Increased ventilation will make the entire roof cold and reduce or eliminate ice dams.