Attic Ventilation 1 300 Rule

Owens corning recommends a balanced ventilation system based on the u s.

Attic ventilation 1 300 rule.

In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq. And this guideline you ll need a. Most codes use the 1 300 rule for minimum residential attic ventilation recommendations. 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. 1 500 square feet 300 5 square feet. Nrca guidelines regarding attic ventilation nrca recommends designers provide at least 1 square foot of nfva for every 150 square feet of attic space 1 150 ventilation. The 1 300 rule is a general rule and does not apply to all situations.

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. 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. Ft of attic space 1 square foot of ventilation is recommended. See how simple.

Now let s figure out how much ventilation space we need. Here are the answers to the five most frequent questions pertaining to calculating attic ventilation. Building codes vary. Ok so now we know the square footage of the attic area to be ventilated.

Remember the minimum area requirement when using a continuous system is a ratio of 1 300. 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. 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. Mostly i ve seen the 1 300 rule specified for attic ventilation but i ve also seen 1 150 mentioned.

But when i do the math that only gives me. Local building codes when stricter take precedence. Based on your 1100 sq. For every 150 square feet sq.

Roof ventilation 1 which states in part 1 square foot of net free area for every 150 square feet of attic floor. 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. In no case should the amount of exhaust ventilation exceed the amount of intake ventilation. Always consult a design professional for cathedral ceilings insulated roof decks etc.

With the amount of needed attic ventilation. Hvi says to use 150 when there s no vapor barrier and 300 when there is.