# Debating Attic Ventilation Pros and Cons



## Ed the Roofer (Dec 12, 2006)

Well, how many sources do you guys have that show by real world experiences and documentation or laboratory controlled experiments, besides the typical ventilation manufacturers and HUD/FHA guidelines and shingle manufacturers warranty requirements which verify the practicality of proper attic ventilation bening a necessity.

Ed

I have a debate going on in another forum, which has significant opposing data defying the conventional wisdom to use a properly ventilated attic system, from a building science point of view.

Go dig out some links and identify your sources so we can all build up a larger library of ventilation wisdom.


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## thom (Nov 3, 2006)

Ed, I think an awful lot has to do with the climate you're working in. The issues in a moderate and dry climate are much different than Chicago.


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## Ed the Roofer (Dec 12, 2006)

The Building Science expert I am having lengthy discussions with seems to believe that it is the colder climate where the disparities are most noteworthy.

But, he is from Can a da, so what does he know, Aaaa.

Ed


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## Chris Johnson (Apr 19, 2007)

Ed;

I don't know the science behind it but for the past few years on houses I have worked on (ICF walls) people want to complete the package with the best energy efficiency possible. 

One ICF manufacturer I deal with sells a product claiming the best roof insulation, it is essentially sheet foam 7" thick attached to the underside of the bottom cord thus allowing full attic ventiltion - only problem is this method is cost prohibitive to most people and even people who can afford it most raise their eyebrows at the cost!!

I also recommend Demilac to people and Demilac has an approved detail where their product is applied directly to the underside of the roof deck and encapsulates the top cord right from ridge to top plate leaving the attic as conditioned space - no ventilation

Be careful arguing with a Canadian, you will find that the USGBC looks up to how they build in Canada, anyone who has mastered building in a climate that has temperature fluctuations of 100 degrees in a 12 month cycle knows what the hell their doing.


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## Tom M (Jan 3, 2007)

Ive repaired more sheathing due to dry rot from people stuffing insulation in the rafter bays to finish an attic than actual water damage.


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## thom (Nov 3, 2006)

Ed the Roofer said:


> The Building Science expert I am having lengthy discussions with seems to believe that it is the colder climate where the disparities are most noteworthy.
> 
> But, he is from Can a da, so what does he know, Aaaa.
> 
> Ed


I believe it. Cold climates will give you condensation on the underside of the deck. Warm dry climates don't have the same issues. 

I built in Chicago prior to moving to Albuquerque in 1981. I had a wintertime callback on a large addition with a reverse gable roof. The addition had a wet ceiling along the entire wall common to the existing house. The underside of the roof decking of the house (not addition) had a 1/8" ice covering throughout. The sun would warm it enough that it ran down the sheathing and dripped out the eaves, except at my addition. The issue was trapped moisture and condensation. Something that's not an issue in Albuquerque.


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## dennis (Nov 17, 2004)

Hi Ed

I have not found much in the way of useful scientific studies dealing with ventilation. There are some abstracts out there on the web that look interesting, but I'm too cheap to fork over the 25 bucks to download the full paper.
Seems to me the info on the ventilation websites is appropriate only in perfect conditions that conform with what they are selling, and the manufacturers are just covering their butts and putting up hurdles with their recommendations. In the meantime selling more of their own extras and accessories. From what I've read the 1/300 venting rule is based on a flawed study done many years ago.
I don't know much about new construction. Most of my work is on old, 70+yrs, houses. My opinion is that each house has to be looked at individually, weighing all the different variables, and addressing the problems.

I've started a couple pages on my own website concerning the basics of ventilation. 
http://roofersreview.com/Ventilation
http://roofersreview.com/htmlpage2

Can you give me a link to your current debate?


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## Ed the Roofer (Dec 12, 2006)

Hi Dennis,

No paper out on the internet will require payment for it if you know how to search for it properly. Type in the title of the abstract or white paper or technological report in Google and try it with and without the authors name after a comma and a "by John Doe", and I usually find a free version of what some other site is trying to charge for. I can only recall SMACNA architectural sheet metal detail drawings as being the one case where I have not yet been successful.

Yeah, I was trying to hold off on the link for a little while to see if anyone here had anything newer and more progressive thinking regarding either the pros or cons of attic ventilation.

The link is:

http://www.nachi.org/forum/showthread.php?t=19078

Currently there are already 80 posts in this linked thread.

It is loaded with a lot of good debateable information and also thumbnail photos and also over 2 dozen other links with sources supporting both sides of the question.

The research against any attic ventilation is limited to a handful of individuals who point out only the facts which support their conclusions and not actual long term case studies, but they make a persuasive argument if I did not have 29 years of actual hands on experience. Maybe things are different in either a laboratory controlled condition or in continuaosly colder climates, such as Canada.

Ed

P.S. I already have seen your roofers review pages and previously saved them to my favorites from that other roofing forum site. I have not participated in that one too much, as the subject sequence is harder to follow than over here and a few others I am in.


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## 747 (Jan 21, 2005)

I say turbine. Unfortunately a lot of roofers don't like them because of the high visible look.


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## Ed the Roofer (Dec 12, 2006)

Only works when the wind is blowing.

Rusts out and stops spinning.

Birds nests clog up the exhaust.

Oh, and by the way, they look ugly.

Ed


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## Joasis (Mar 28, 2006)

We have been putting down solar guard insulation under metal panel roofing now, and the difference in attic temps is amazing. No roof deck, just strapping. Of course, this won't work with comps, but I keep hearing about a decking that has the reflective side.


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## woodman42 (Aug 1, 2007)

We have 1/2" foil faced osb that works well at reflecting radiant heat.
Here in Texas it works really well.


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## Ed the Roofer (Dec 12, 2006)

Does the radiant barrier reflective foil face up towards the roof or down towards the attic?

Ed


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## Joasis (Mar 28, 2006)

Foil up....30 to 40 degrees cooler attic temps.


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## POOLMANinCT (Oct 7, 2006)

tom m said:


> Ive repaired more sheathing due to dry rot from people stuffing insulation in the rafter bays to finish an attic than actual water damage.


I bought this house last july, replaced a 7yr old roof, in november. prior owner stuffed rafters....
roofer told me it choked & baked it in no time...


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