Attic Ventilation 1 300 Rule

Here s a rule of thumb to follow.

Attic ventilation 1 300 rule.

Roof ventilation 1 which states in part 1 square foot of net free area for every 150 square feet of attic floor. Building codes vary. Ft of attic space 1 square foot of ventilation is recommended. The 1 300 rule is a general rule and does not apply to all situations.

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. 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. Of vent for every 300 sq. With the amount of needed attic ventilation.

Based on your 1100 sq. Hvi says to use 150 when there s no vapor barrier and 300 when there is. Most codes use the 1 300 rule for minimum residential attic ventilation recommendations. Here are the answers to the five most frequent questions pertaining to calculating attic ventilation.

Remember the minimum area requirement when using a continuous system is a ratio of 1 300. Ok so now we know the square footage of the attic area to be ventilated. Local building codes when stricter take precedence. 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.

So in our example we will divide the 1 500 square feet by 300. In no case should the amount of exhaust ventilation exceed the amount of intake ventilation. 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. 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.

See how simple. Mostly i ve seen the 1 300 rule specified for attic ventilation but i ve also seen 1 150 mentioned. 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. But when i do the math that only gives me.

1 500 square feet 300 5 square feet. For every 150 square feet sq. 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. Owens corning recommends a balanced ventilation system based on the u s.

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