When determining ventilation, remember the following:

1. Intake and exhaust ventilation should be installed at an approximate one to one (1:1) ratio. More at the eaves is better if it can be attained.
2. The 1/300 rule - 1 square foot of attic ventilation (Net Free Vent Area) per 300 square feet of attic floor space.
3. No attic vents should be installed between the intake and exhaust vents.
4. There should be at least three feet (3') of vertical distance between the intake vnets and the exhaust vents.

SOME NOTES:

1. FHA Guidelines recommend the 1/300 rule. Some building codes require the 1/150 rule. When using the example above, adjust your numbers accordingly.
2. The Home Ventilating Institute (HVI) recommmends a 60/40 ratio where 60% of the total ventilation is for intake and the remaining 40% is for exhaust.
3. Some material manufacturers will not honor their warranty unless attic ventilation has been installed.

The information found on this page is for informational purposes. For specific ventilation requirements in your area, consult your local building code authority.