Proper roof ventilation

[jpfaff6]

The weatherization industry wants people to seal up their attics and crawl spaces and the roofing industry wants people to vent their attics. And others want crawl spaces vented. What is the better choice?

[David Meiland]

The weatherization industry wants people to seal up their attics and crawl spaces

I don't agree with this statement. The weatherization industry wants people to define a thermal boundary. The attic or crawl space may or may not be included, based on many factors that vary from house to house and region to region. What's right in one instance may be fatal in another.

[jpfaff6]

I agree with what you are saying. To be more specific I like in Indiana and am a certified weatherization tech. We were trained by the state to blow cellulose over eve soffit without using a baffle. I personally don't agree with it but that is what we have to do. And we are told the tighter the attic and crawl space is the better.

[David Meiland]

Interesting. Assuming that they have studied this, they apparently believe that eliminating the eave venting (while presumably leaving the ridge venting) will reduce wind-washing of the insulation and reduce heat loss, without creating humidity problems.

[Bluewoodrock]

I agree with what you are saying. To be more specific I like in Indiana and am a certified weatherization tech. We were trained by the state to blow cellulose over eve soffit without using a baffle. I personally don't agree with it but that is what we have to do. And we are told the tighter the attic and crawl space is the better.

What code do you use in Indiana? You may be violating code- The Massachusetts code specifically states you can't have an unvented assembly unless you use an air impermeable insulation material- which basically limits you to closed cell foam.

Of course the weatherization programs teach exactly what you're saying. I was at a training a few months ago where the instructor was saying to just dense pack roofs- I hauled out my code book- he had no good answers...

Both unvented and vented can be good approaches depending the situation, but just blowing cellulose over the vents seems like a bad idea to me.

[John B]

Hey Mike,
Nice post
for a foam guy ;-) ... you are OK

I did not think it was possible to fill framing cavities with Closed Cell Foam.
You corrected me.
There is a good illustration in ths month's(JLC June 2010) David Joyce Article.
Did you work on that project?

[Walter S.]

If they eliminate the eave venting but leave the ridge venting where will the intake air come from. Everything I have read (aside from the closed cell foam method) teaches balanced ventilation system that has 1 sq. ft. of ventilation per 300 sq. ft. of attic space with 50% of that being intake and 50% exhaust. And if your going to have more of one than the other it needs to be intake so that you don't create negative pressure in the attic.

[Bluewoodrock]

Hey Mike,
Nice post
for a foam guy ;-) ... you are OK

I did not think it was possible to fill framing cavities with Closed Cell Foam.
You corrected me.
There is a good illustration in ths month's(JLC June 2010) David Joyce Article.
Did you work on that project?

Yeah, well your OK for an architect(?)

And I'm actually a carpenter/builder/foam guy- all the slashes are probably what make me OK.

And yes we did do the insulation on that project- which, when it was blower door tested, got the whole Building Science Corp office in a tizzy because it was the tightest they had ever seen.
I forget the exact rating- does it mention in the article? I haven't got my june issue yet.

[John B]

And yes we did do the insulation on that project- which, when it was blower door tested, got the whole Building Science Corp office in a tizzy because it was the tightest they had ever seen.
I forget the exact rating- does it mention in the article? I haven't got my june issue yet.

Mike,
The David Joyce article and project are very good....
Nice work on the foam & insulation / air sealing
The blower door result was 0.72 ACH50

Edit to say..
I am an Architect from Dallas...
it used to say on my profile...guess it fell off
I will update my proflie

[Bill Robinson]

I am peripherally involved in weatherization training and will share my perspective.
The industry has grown so quickly that there are decision makers and trainers who do not understand the science part of building science.

I seriously doubt the official stance of the Indiana Wx group is advocating what has been described here.
I am guessing it is more likely the instructor does not get it.

In the last few months I have attended the DOE weatherization conference, last year in Indiana by the way, and the ACI conference recently held in Austin.
At neither of these conferences did I hear we should do this.

BR