Determine the total net free area required.
Eave input vent area to floor square ft ratio.
Ok so now we know the square footage of the attic area to be ventilated.
40 x 25 1 000 square feet of attic area 2.
1 100 square inches of intake net free area needed.
30 lineal feet required.
150 6 6 square feet of total net free area 3.
If you have 3 000 square feet of attic space this equates to 20 square feet of ventilation needed.
So in our example we will divide the 1 500 square feet by 300.
A 6 x 12 vent would equal 72 sq.
1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below.
The irc adds that the nfva ratio can also be reduced to 1 300 if 50 to 80 of the required ventilation is located in the upper portion of the attic or cathedral ceiling and the rest is located at the eaves with the upper vents at.
Say the contractor is standing in front of a house that has an attic with 2 200 square feet.
Divide the square footage by 150 to calculate the area of ventilation needed since you need 1 square foot of vent space for each 150 square feet of attic space.
For example a single story house with 2000 square foot of roof floor area would require 13 3 square feet or 1920 square inches of vent area.
1 500 square feet.
Now let s figure out how much ventilation space we need.
That determines the total amount of net free area needed to properly ventilate the attic.
Calculate or enter the square footage of the attic or area to be vented.
This ratio is required for modern insulated homes.
This is distributed between under eave net free vent area and the ridge in a ratio of 60 under eave and 40 in the ridge.
The next step is to select a suitable exhaust vent and intake vent that fits the roof design for best performance and best aesthetics.
In no case should the amount of exhaust ventilation exceed the amount of intake ventilation.
Based on your 1100 sq.
Remember the minimum area requirement when using a continuous system is a ratio of 1 300.
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.
2 200 2 1 100 square inches of exhaust net free area needed.
And this guideline you ll need a minimum of.
For round vents multiply the radius of the vent half the diameter times itself squared then multiply the total by 3 14 pi and divide by 144 to find the number of square feet r in inches x 3 14 144 sq.
In divided by 144 equals an area of 0 5 sq.
Always have a balanced ventilation system.
