# Efficacy of passive roof vents?

**URL:** <https://boards.straightdope.com/t/efficacy-of-passive-roof-vents/687997>\
**Category:** Factual Questions\
**Created:** [May 8, 2014, 7:07pm UTC](https://boards.straightdope.com/t/efficacy-of-passive-roof-vents/687997 "2014-05-08T19:07:15Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\
**Post date:** [May 10, 2014, 5:42pm UTC](https://boards.straightdope.com/t/efficacy-of-passive-roof-vents/687997/21 "2014-05-10T17:42:07Z")

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> [@FluffyBob](#):
>
> One of the most popular solutions now is to use [continuous ridge ventin](https://www.google.ca/search?q=continuous+ridge+vent&rlz=1C1GIGM_en-GBCA550CA550&oq=continuous+ridge&aqs=chrome.1.69i57j0l5.7031j0j7&sourceid=chrome&es_sm=122&ie=UTF-8)g. The idea is it allows even venting all along the roof rather than just at a few vents and encourages a direct flow of air from the soffits to the ridge. If the roof was not sheathed for continuous vent, an inch gap has to be cut either side of the ridge blocking. Standard practice is to block off gable vents and make sure soffit venting is sufficient. Modern aluminum vented soffit is good, solid soffit may need additional vents added. We use this on all the re-roofs we do (hail or fire restorations).
> 
> Inspectors have told me that the problem with wirlybirds is a strong wind can produce more negative pressure than soffit venting can make up for, resulting in moisture laden air being drawn into the attic from living space.

Good information; thanks. Looks like there is an old gable vent on the front of the house, but I can’t tell if it’s blocked or not, and can’t/won’t get up that high to check it. Maybe I can see it from the crawl hole.

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**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\
**Post date:** [May 10, 2014, 6:46pm UTC](https://boards.straightdope.com/t/efficacy-of-passive-roof-vents/687997/22 "2014-05-10T18:46:25Z")

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> [@FluffyBob](#):
>
> Inspectors have told me that the problem with wirlybirds is a strong wind can produce more negative pressure than soffit venting can make up for, resulting in moisture laden air being drawn into the attic from living space.

Did they explain how that happened? Unless a bathroom vent is open to the attic I don’t understand how that’s possible?

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**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\
**Post date:** [May 10, 2014, 6:50pm UTC](https://boards.straightdope.com/t/efficacy-of-passive-roof-vents/687997/23 "2014-05-10T18:50:12Z")

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penetrations of the vapor barrier in the ceiling and upper walls. through utility penetrations also.

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**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\
**Post date:** [May 10, 2014, 6:57pm UTC](https://boards.straightdope.com/t/efficacy-of-passive-roof-vents/687997/24 "2014-05-10T18:57:49Z")

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> [@johnpost](#):
>
> penetrations of the vapor barrier in the ceiling and upper walls. through utility penetrations also.

wow that’s some serious suction.

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