My house does not have soffit vents. The overhang at the eaves is too small. The ceiling leaks were sealed up by an HVAC company about 10 years ago. They also blew in insulation to an R30 level in the attic. There are gable vents (22” rounds) on both ends. A roofing company just put a new roof on and added a ridge vent. Am I ok to leave it alone? Do I need to put in a gable fan for air intake?
The Code requires Attic Ventilation to be “cross ventilation “ and shall be 1/150th the area that is to be vented. (See ICC R806 Vents.)
However, there is one exception: The attic ventilation can be reduced to 1/300th the area to be vented provided one of the following items are met:
a Class I or II vapor retarder is installed on the “warm-in-winter” side of the ceiling, or
not less than 40% and not more than 50% of the ventilation is located in the upper portion of the attic. The upper portion is defined as: “Upper ventilation shall not be lower than 3’ below the ridge or highest point of the roof. “ (See ICC R806.1.2.)
So, if your attic is 20’ x 40’ then the area is 800 square feet. So with ridge vents you need 1/300th the area, or 800 / 300 = 2.67 square feet of vents. You can calculate how many square feet of vent you have and know if your venting meets the Code minimum. If so you should be ok.
So, you can see there is clearly a benefit to having ridge vents, gable vents, etc.