The downside of attic ventilation fans.
How many roof vents do i need for my house.
As a general rule your roof needs 1 square foot of vent area for every 150 square feet of attic space.
Choose one of the following products to meet the recommended exhaust nfva of 528 square inches.
Thus if your attic is 450 square feet you need roof vents equaling 3 square feet.
Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation for every 300 square feet of attic floor space evenly split between intake and exhaust.
Without exception you should talk to a professional to determine what your home requires.
Choosing round soffit vents for.
Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation.
Use the calculator below to find out how many exhaust and intake vents you will need on your house.
That said air resistance and interference such as vent grates reduces the area of true ventilation.
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.
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.
Hvi recommends a ratio of 60 to 40 for soffit ventilation to gable or ridge ventilation.
Rafter vents or insulation baffles install in any rafter space to create narrow gaps that direct fresh air from the soffit vents to the peak of the roof.
Ideally there should also be plenty of soffit intake space their calculations recommend 336 net square inches of open soffit ventilation to supply 700 cfm.
For the number of soffit vents in the example divide 8 square feet of ventilation needed by 0 5 for the number of rectangular vents required 16 in the example.
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.
Always have a balanced ventilation system.
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.
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.
In no case should the amount of exhaust ventilation exceed the amount of intake ventilation.
