Hello, I purchased a house that has a tiny sofit with no room for vents but it has a ridge cap the length of the house. For proper ventilation I wanted to add a couple low profile roof vent toward the bottom of the roof like the image below. I am planing on finishing the attic so the vents would be behind the kicker or side wall and would be able to exhaust out the ridge. The room is going to be 16' X 35' finished. How do I figure out how many I will need to add? Thanks!
Many of those type of vents are not made for intake. I would double check your soffit, as using continuous soffit venting does not take much space (please take pictures for us!)
You need a 1/300 area of Ventilation/ceiling space. Measure your ceiling space, divide it by 300, and that is your minimum ventilation needed. Example: 900sqft of ceiling = 3sqft of venting. Ideally the venting should be split 50/50 at the top and bottom, which means 1.5sqft of venting at the ridge, and 0.75sqft of venting at each soffit (assuming two soffits on a typical gable style roof).
It depends on the type of ridge vent (pictures would help) but typically they are 0.1sqft per foot. Example: 30 feet of ridge = 3sqft, which means you will need 1.5sqft at each soffit in order to satisfy the 50/50 rule.