I need some advice. I need to replace the roof over my attic. It’s a bit over 1000 square feet. At the moment, the only ventilation comes from two small gable vents. The roof has no eves or soffits. The attic is poorly insulated, so I also plan to have it air sealed and insulated with blown-in cellulose.
The ventilation is inadequate. I would like the attic to be cooler in summer. In winter there is a risk of ice dams (I live in NY), although I’ve never seen any evidence of them. After some research, it seems I have two ventilation options. Which of these, if any, makes more sense?
- Add a ridge vent and an edge vent such as this one. There are a couple of issues with this approach. One is that I have a 45 foot ridge and only one edge. The other side of the house has mostly vaulted ceilings. The diagram found here shows how it’s arranged. That means that a ridge vent with 18 inches NFA/foot will have twice the exhaust venting capacity as the edge vent at 9 inches/foot.
The other problem is that the attic is at most 3.5 or 4 feet tall from the ceiling joists to the ridge pole. Is this enough height difference to get good air movement from the edge intake to the ridge exhaust?
- Add a powered roof vent such as QuietCool’s “smart roof mount attic fan”. In this case I’d have to add a significant amount of intake venting as the two gable vents probably don’t add up to anywhere close to the recommended 4 square feet of NFA. I would probably add some turtle vents. The right side of the roof is not visible to anyone so it can be ugly - but I do want to minimize the potential for leakage and ice dams. Does it matter where they go on the roof - up close to the ridge or down by the edge? Or halfway up? Or is there a better intake venting option?
Any advice would be appreciated. Thanks!