Attic Ventilation

[kurt]

In recommending ridge vents, I am presupposing they are installed satisfactorily.

[Les]

Jess,

Sounds like you have a good handle on the wonderful world of attic ventilation! Yep, I think your calculations are correct. Please forgive me for stirring things up a little bit, but I think we all learned a tad more about ventilation.

Good question!

Chad,

How often have you seen ridge vents act as snow fences? Nice clean 8" line of snow in the attic.

[stouto]

Food for thought. The info seems logical to me. but I am only a homeowner.

http://roofersreview.com/PowerVentilators

http://roofersreview.com/Ventilation

http://roofersreview.com/ShortCircuitMyth

[hausdok]

Hmm,

A blog that uses seemingly authoritative articles with no attribution. I wonder who spends more time in attics looking at the underside of roofs and examining ventilation issues; home inspectors or roofers?

Certainly, here in the northwest I've seen hundreds of examples of gable vents short circuiting ventilation in attics when ridge vents and soffit vents were added to old homes and I've found my fair share of fungi on the underside of roofs in new homes less than two years old where the builders have used a belt and suspenders approach and have combined gable vents with eave and pot vents placed near the ridge or ridge vents.

I tend to believe stuff written by folks who make their living researching this kind of stuff and writing about it; folks like Dr. Joe. If Dr. Joe were to state that the gable vent short circuiting is a myth, I'd probably believe him but I have a hard time believing an anonymous roofer.

The original poster lives in Georgia. click here for Dr. Joe's corporation's take on designs that work in the Atlanta region. Here's what they say about attic ventilation for that area:

Vented attic – Soffit and ridge vents provide more effective attic ventilation than gable-end vents. Gable exhaust fans do not provide effective attic ventilation. They are generally temperature-controlled, when relative humidity is often the condition that requires higher ventilation rates. This can also depressurize the house causing loss of conditioned air. Generally, the area of the gable and soffit vents, combined with the leakage of the attic ceiling, is such that the fan pulls air not just from the exterior vent but from the conditioned space below.

Spend a little time here if you really want to start understanding this stuff.

ONE TEAM - ONE FIGHT!!!

Mike

[Chris Bernhardt]

My favorite source on the subject is William B. Rose. His book "Water in Buildings, An Architect's Guide to Moisture and Mold" is one of my most treasured in my library.

Chris, Oregon

[hausdok]

Hi Chris,

If you've ever wondered how far back some of these code requirements go and what the basis for them is, you can go here.

ONE TEAM - ONE FIGHT!!!

Mike

[Chad Fabry]

Chad,

How often have you seen ridge vents act as snow fences? Nice clean 8" line of snow in the attic.

I see the evidence more often than the actual snow, but I've been in attics when it's blustery and they admit plenty of weather.

[kurt]

What about those fuzzy mesh type that get shingled over? I've got those on my house, and I've never had a drop of water or speck of snow.

I see plenty of weather come through Cor-Vents or the other plastic types.

[drcr]

hausdok,

Just curious, what part of those "seemingly authoritative articles ", do you not agree with?

[hausdok]

I don't agree with the assumptions he makes about power ventilators, most of his ventilation basics stuff or his claim that gable end vents don't short circuit a ridge vent.

I'll believe Joe Lstiburek, Yost, and others who can prove their theories with solid research.

OT - OF!!!

M.

[drcr]

Hi Mike,

I went to the BuildingScience website and searched for the term "short circuit". No luck.

A lot of info on ventilation, but I could not find anything about short circuiting the attic ventilation thing.

Maybe you could point me to Listurbek's report on the subject or some other solid research.

Thanks

[hausdok]

Hi,

I think short circuiting is a term that came from this profession. If you go to the building science site and study the technical documents contained there you'll find what you're looking for. I've linked one of those above.

OT - OF!!!

M.

[Gibsonguy]

Hi guys,

Just my 2 cents, but doesn't anyone use maxi vents? Up here in Montréal they are the norm when reshingling roofs, and seem to work well.