Attic Ventilation Needs

Feet of attic space divided 50 50.

Attic ventilation needs.

His home is 48 feet long and has a ridge vent that measures 46 feet. In cold climates the primary purpose of attic or roof ventilation is to maintain a cold roof temperature to control ice dams created by melting snow and to vent moisture that moves from the conditioned space to the attic ventilation acts to bypass the vapour barrier created by most roof. How to determine whether you need better attic ventilation. The following are the requirements taken directly from the irc.

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. 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. That said air resistance and interference such as vent grates reduces the area of true ventilation. Let owens corning roofing help you calculate exactly how much ventilation you will need for a healthy and balanced attic with our 4 step ventilation calculator.

In other words the entire vent opening doesn t count as vented space. In the winter warm moist air seeps into the attic from the living space below. That cuts cooling costs and prolongs shingle life. The majority of the requirements related to attic ventilation have not changed much from the previous editions.

His next step is to calculate the total amount of ventilation that he has in his attic. In the summer good attic ventilation reduces heat buildup. 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. Your soffit ventilation actually needs to be considerably more than 336 net square inches to supply a 700 cfm fan system or the fan is going to pull the air it needs through unsealed holes and gaps in the attic floor from the conditioned living space.

Throughout the balance of this digest the terms attic and roof will and can be used interchangeably. He has calculated that he needs 7 36 square feet of ventilation space for his attic. The ventilation amount and opening size requirements can be found in section 806 roof ventilation of chapter 8 roof ceiling construction. Good ventilation allows the heat and moisture to escape.

Enter square footage calculate or enter the square footage of the attic or area to be vented. Intake vents located at the lowest part of the roof under the eaves allow cool.