Ridge Vent . . . and Nothing But the Ridge

Can anyone convince me that this picture shows anything other than the fact that the ventilation provided here is effective only in the first five inches down from the ridge? And yes, there is continuous soffit venting that is baffled and open to the outside.

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Comment by Bob Mariani on December 29, 2011 at 3:30pm

Still more natural air flow should persist.  I believe the soffit venting is insufficient.  The air movement should be equal between the ridge and the soffit vents.

Comment by Ed Voytovich on December 29, 2011 at 2:55pm

Bob . . . I'll refer to the black snot as "mildew" in hopes of assuaging to the extent possible the anxiety of the homeowners and the desire of their lawyers for a new Mercedes.   

Thanks for pointing out the fact that the cut-out is somewhere around an inch or less on each side instead of the manufacturers' recommended inch and a half.  Still, could another 3/4" on each side make that great a difference?

There are no gable end vents, and the same pattern of mildew extends the entire length of the ridge.

I suspect that this condition is more typical than not of ridge vents.  When the wind blows across the roof  and the ever-popular Bernoulli's Law (http://scienceworld.wolfram.com/physics/BernoulliEffect.html) comes into play, the downwind side of the vent sucks air out of the attic.  I suspect that it is most likely to take the makeup air from the nearest source (which is the other side of the ridge) than from either gable vents or vents in the soffit.  My thinking is that the high-moisture conditions in this particular house created an interesting experiment, but I am grateful for other thoughts and possibilities.

Comment by Bob Mariani on December 29, 2011 at 1:52pm

Ed, is that mold on the discolored section of the sheathing?  The vent opening should have been larger.  Only a small air flow is occurring.  Also be sure no gable vents are still opened that will short circuit the soffit to ridge vent airflow.

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