Monday, September 7, 2009

Ridge Vent to the Rescue!

Problem: Not enough outflow area for hot air to leave the attic
Problem: Existing outflow vents on the roof are not even near the peak

Searching the web for solutions to these problems yielded a growing consensus: the best way to ventilate a modern attic is a combination of soffit vents for air intake into the attic, which I had recently cleared, and something called a ridge vent for outflow of the hottest air from the attic. The ridge vent is nothing more than a couple of long but narrow slits cut through the roof beside the longest peak at the top of the roof. For my house, the longest peak doesn't run the full length of the house, but it does run about 2/3 of the length. The ridge vent also includes a covering made by a ridge vent supplier that gets installed over the top of the slits so that rain does not fall right into the attic. There is some art and value added by the different vendors in this component - different designs allow better or worse airflow, are better or worse with wind-driven rain, etc.
The thing that Energy Efficiency Man likes about ridge vents is that they are simple, have no moving parts to wear out, and will require very little maintenance. For some ridge vent systems, there is a filter over the slits that will require changing every few years, but that is about the extent of ongoing maintenance. Finally, in my particular case, the fact that this solution is placed at the peak of the roof means that it solves both of my problems in one fell swoop.
Before we proceed to my particular experience with ridge vents, I should note that there are some vocal detractors of the technology out there. I have seen claims (mostly from one person who sells a competing system) that ridge vents won't work well because the covering forces hot air to flow down momentarily, which it doesn't want to do, to work its way out of the attic. While this is true, I would challenge folks to design a roof vent that doesn't require something like this and still blocks rain from entering the attic. Most existing vents have this problem. Furthermore, and this is yet another area where aspiring Efficiency Men and Women out there should consider their own local weather patterns, my area has pretty consistent winds through the summer months, and in my case, those winds flow across the roof perpendicular to the wind. Due to the Bernoulli effect that we all know and love, that familiar physics principle that makes sailboats move and airplanes fly, the prevailing summer winds create a low pressure area on the downwind side of my ridge, and a higher pressure area on the upwind side, creating a "pump" that helps move the air out even faster than hot-air convection normally would. At least this is true in theory; I have no easy means to test it.
But back to my own experience. In short: I decided on the ridge vent, and I had the good fortune to find a workman who would buy and install a ridge vent for me for a very good price. In one afternoon he had cut the requisite long strips out of the roof, and unrolled and installed the ridge vent rain baffle/air filtration system over the long cuts.
However, one question remained foremost on my mind: would the new outflow area be enough to balance the intakes? The answer to that question will have to wait...

Solution: Ridge vent installed at the very top of the roof

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