do ridge vents really work ?
When I install the roofing on my house, I am planning on continuous soffett and ridge venting. I have always heard that a continuous ridge vent, along with adequate soffett vents, is the optimum passive venting method.
On Roofing.com, however, I came across this link, http://www.savenrg.com/venting.htm, that says ridge venting doesn't work.
Of course, the article is by a company that's advertising its own venting product, so there may be some bias there.
Basically, what they seem to be saying is that because ridge vents or ridge trims are shaped like an inverted 'V', that they block the hot air from escaping.
What's the general consensus on whether or not ridge vents work ?
Although I haven't measured the temperature up there I think my roof ridge vent is not working since it feels very hot up there. The roofer used a material somewhat like coarse steel wool to cover the ridge opening and keep insects out. Unfortunately I think that that material got too squished during installation to let air out quickly.
An alternate material consists of layers of corrugated plastic similar to corrugated cardboard. This is rigid and does not squish. I put some of this on a ridge vent on a shed I built from scratch and the shed is not hot in summer. A notable difference from the steel wool like material is that I can see daylight through the ridge vent with the corrugated material.
It's not the slight downgrade the hot air must take when exiting the roof vent but rather how freely air can flow out.
There is some merit to the arguments in that link, but there is alot of questionable material as well. The terra cotta roof shown down the page a bit that has the "dormers" both high and low would be against the code requirements of my region if those were the only methods of venting provided.
Does the "V" trap heat in the attic? I woud say no. The convective pressures created from the temperature differential between the soffit and ridge vent are great enough to outweigh the 1" or so deep V.
Are ridge vents not functional in snow covered conditions? I would say, no they are not functional if covered, but neither are those dormers shown on the link.
Are gable fans the best? Not unless there are supplemental fans within the attic space to exchange the entire volume. Gable fans tend to create a kind of "funnel" of air between the intake gable vent and the exhaust gable vent. If there are continuous soffit vents, the fan pulls from the closest ones and leaves the balance of attic volume un-touched. The supplemental fan would circulate the attic air and allow for a proper exchange when the exhaust fan is in operation.
Are roof-top ventilators the best? These work about the same as the ridge and dormer vents but have a better resistance to snow covering.
It is also argued that not all ridge vent assemblies are functional because of wind driven pressures that don't allow the ridge vent to passively act. The ridge vents with "dams' on the external side block the wind and enhance the movement of air through the ridge vent. The dormer's they showed do not have a method to counteract this and the wind would govern the air flow direction and how much is exchanged.
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