1 500 square feet 300 5 square feet.
Attic ventilation 1 300 rule.
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.
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.
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.
Building codes vary.
Remember the minimum area requirement when using a continuous system is a ratio of 1 300.
But when i do the math that only gives me.
Ft of attic space 1 square foot of ventilation is recommended.
Roof ventilation 1 which states in part 1 square foot of net free area for every 150 square feet of attic floor.
Of vent for every 300 sq.
In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq.
Most codes use the 1 300 rule for minimum residential attic ventilation recommendations.
In no case should the amount of exhaust ventilation exceed the amount of intake ventilation.
Local building codes when stricter take precedence.
Hvi says to use 150 when there s no vapor barrier and 300 when there is.
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.
Mostly i ve seen the 1 300 rule specified for attic ventilation but i ve also seen 1 150 mentioned.
For every 150 square feet sq.
Now let s figure out how much ventilation space we need.
Ok so now we know the square footage of the attic area to be ventilated.
See how simple.
And this guideline you ll need a.
Based on your 1100 sq.
With the amount of needed attic ventilation.
Here s a rule of thumb to follow.
Here are the answers to the five most frequent questions pertaining to calculating attic ventilation.
The 1 300 rule is a general rule and does not apply to all situations.
So in our example we will divide the 1 500 square feet by 300.
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.
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.
