any idea how to stop wind blown rain on gable end vents? – or is it impossible?
mine are wood – home/job site made I think
and I wonder if the vent “slat” angle is too flat – during the hurricane last weekend 50-60 MPH NE winds I had some rain blown in.
any design guidelines
maybe I need an inline valve like on submarines
Replies
A popular feature in some early Florida homes was provision for blown in rain. Hurricane winds and the radical ventilation need of pre-air conditioning run counter to each other.
The first time I saw this was a ridge vent on a commercial building. Wood slats with a full inch between them were stacked so the linear cupola stuck up a good foot above the normal ridge. With strong wind driven rains this would let in gallons. Their solution was to install a galvanized steel tray under the vent.
The tray was something close to 2' wide and protected both the drip line and any conceivable angle the wind would likely travel. The cupola had a drip edges under it on the inside to keep the water from adhering to underside of the roof deck. The rafters had small bits of molding to accomplish the same thing.
The tray was tilted and a flange welded on allowing a pipe to be attached. This led out through a hole in the the gable end. Any rain that made it end hit the tray and was ejected outside. Nothing complicated. Everything passive. The big advantage was that this allowed the ridge vent to be large and very effective. Even without AC the building, with a steel roof, remained relatively comfortable.
In your case drip edges could be applied to the inside of the vent and a tray fitted. To gauge the size figure that rain, once blown into the calmer attic, won't travel very far so a 45 degree angle should cover any contingency. The tray could be equipped with a short nipple that would stick out of the gable end below the vent and would tilt toward this end. Plumbers strap screwed into the rafters would hold the tray on the side opposite the vent. The gable end would get a couple of screw into the gable end framing.
I have seen this on a few older Florida homes where a whole house fan demanded robust attic venting but also an eye to wind blown rain. No expensive, complicated, noisy or Murphoid moving louvers needed.
Once in place you could modify or replace the existing vent with one with larger openings. I have found that most commercial vents are so concerned with rain and bug entry that they largely fail as ventilation. If not when initially installed then with age and a little dust buildup.