Porch Ventilation

LESLIE: Lee is Illinois needs some help with a porch enclosure. Tell us about the problem.

LEE: Well, I’ve got too mushroom vents and it’s an addition to my house and they just haven’t – the roof just didn’t last. I’m thinking of ridge vents for the whole roof and I wondered if there was a vent that would go along a porch roof, kind of where it’s attached, instead of using the mushroom vents. Is there such a thing?

TOM: If the porch roof does not have soffits, you can add something called a drip-edge vent. And what a drip-edge vent does is it, in essence, creates about a two-inch overhang and creates sort of a mini-soffit where you can get some airflow up underneath the plywood sheathing and then that air would run between the insulation and the underside of the sheathing but you need to make sure it has a place to exhaust at the top.

Now, you mentioned that you have some of those sort of mushroom vents. The best thing is a ridge vent instead of those mushroom vents because you get much better circulation. What happens is wind blows over the roof; it depressurizes at the ridge and that draws air out and, at the same time, it gets positively pressurized at the soffit and that pushes air in. And so that sort of cycle repeats itself and it’s much more efficient than any other type of ventilation system including, by the way, a powered ventilator.