Attic Ventilation 1 300 Rule

Local building codes when stricter take precedence.

Attic ventilation 1 300 rule.

Ft of attic space 1 square foot of ventilation is recommended. Ok so now we know the square footage of the attic area to be ventilated. This means that for every 300 square feet of enclosed attic space 1 square foot of ventilation is required with half at the upper portion exhaust vents and half in the lower portion intake vents. Here s a rule of thumb to follow.

According to the 2018 irc code on attic ventilation the minimum net free ventilating area nfva shall be 1 150 of the area of the vented space. In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq. 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. Mostly i ve seen the 1 300 rule specified for attic ventilation but i ve also seen 1 150 mentioned.

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. Of vent for every 300 sq. The 1 300 rule is a general rule and does not apply to all situations. Also when using a vapor retarder in an attic space irc 2012 limits the net free ventilation reduction from 1 150 to 1 300 for buildings in climate zones 6 7 and 8.

1 500 square feet 300 5 square feet. And this guideline you ll need a. 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. Hvi says to use 150 when there s no vapor barrier and 300 when there is.

For every 150 square feet sq. But when i do the math that only gives me. Owens corning recommends a balanced ventilation system based on the u s. Here are the answers to the five most frequent questions pertaining to calculating attic ventilation.

In no case should the amount of exhaust ventilation exceed the amount of intake ventilation. Roof ventilation 1 which states in part 1 square foot of net free area for every 150 square feet of attic floor. So in our example we will divide the 1 500 square feet by 300. Based on your 1100 sq.

Always consult a design professional for cathedral ceilings insulated roof decks etc. With the amount of needed attic ventilation. I m putting in continuous soffit vents on friday hopefully and it s looking like we re going to use the standard 2 wide variety which has about 9 nfa per foot. Remember the minimum area requirement when using a continuous system is a ratio of 1 300.

Building codes vary. Now let s figure out how much ventilation space we need.