Builders refer to this as the 1 in 300 rule and it requires that the total venting space should be at least shared equally between the soffit and roof vents.
How far apart for roof vents.
Otherwise the exiting air at the ridge will usually pull its makeup air from the closer gable end vents and not from the soffit or eaves vents.
Calculate the total vent area needed.
Thus if your attic is 450 square feet you need roof vents equaling 3 square feet.
The federal housing authority fha requirement for attic venting is 1 square foot of venting for every 300 square feet of attic space.
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.
Vegetation must not be allowed to grow within 3 feet of an exhaust vent.
But they do tend to space rafters in one of several industry standard increments typically either 12 16 or 24 inches apart.
This video has examples of both static and ridg.
If your attic floor has a vapor barrier you will need one square foot of nfa per every 300 square feet of attic floor area half of that will be intake half for exhaust.
Exhaust vents must not be allowed to be obscured or hidden by vegetation.
Proper installation number and location of roof ventilation is needed to maximize the performance of a roof.
If you have 3 000 square feet of attic space this equates to 20 square feet of ventilation needed.
Multiply the length of the attic times the width in feet to find the attic area then divide by 150 to find the total square feet of vent space needed.
Roof vents choose one of the following products to meet the recommended exhaust nfva of 528 square inches.
A 50 x 30 attic would have a total area of 1 500 sq.
If there is no vapor barrier double it to one square foot of nfa for every 150 square feet of attic floor space half for intake half for exhaust.
These spacing intervals are measured on center meaning that the measurement is taken from the center of one rafter s horizontal surface to the center of the next rafter.
As a general rule your roof needs 1 square foot of vent area for every 150 square feet of attic space.
In all areas exhaust vents should be at least 1 foot above roof surface.
They should be divided equally between inlet and outlet vents and they can be used in any combination that will work with your roof s design.
Length x width of attic in feet 150 total sq.
This ratio is required for modern insulated homes.
Ventsure 4 foot strip heat moisture ridge vent 27 lineal feet required.
Provides continuous ridge venting continuous soffit venting and then close off those old gable end vents to force the intake air to come where you want it to flow.
Of total vent space needed.
Exhaust vents must be protected against rain and equipped with back flow prevention features e g flap dampers.
