Air Barrier vs. Insulation

[Allan Edwards]

I tried to ask this question at GBA but couldn't get past the secret log-in code :)

Martin said:

Allan,
Q. "Is cellulose as good an air barrier as open or closed cell foam?"

A. No. So seal your ceiling before you insulate!

So I assume drywall is an air barrier for a 2nd floor ceiling that has an attic above it. Are you saying loose insulation above the drywall (cellulose or fiberglass) is not air barrier. If spray foam was used instead of cellulose, does it qualify as an air barrier.

What is the relationship between air barriers and insulation, as well as their individual importance.

[Bill Robinson]

Not GBA Allan but I am working on this a lot here in NOLA and just did some bits in Providence at JLC.

Open and closed cell spray foam meet air barrier requirements when in an assembly, roof, wall floor.

The air barrier association of america has the details and guidelines.

Loose fill, FG and cellulose as well as the other boutique insulation's, do not meet the standards presented by ABAA.

So in a ceiling where the drywall is used as an air barrier, sealed, the loose fill in contact is "approved" as insulation.

Loose fill without an air barrier is a filter. Spray and rigid foam in a cavity forms its own air barrier.

'Zat help?

[Allan Edwards]

So, you could have insulation that provided R-60 but is a poor air barrier, or insulation that is a great air barrier but low R value. Of course you want both, but which is more important in terms of energy use and comfort.

[Bill Robinson]

Allan, I believe that depends on the climate. Here in the hot/humid I would say an air barrier since the hot moist air invading the building when it meets a condensing surface will develop bulk water which will promote mold and mildew as well as decay.

Having said that you really can't separate them when it comes to energy use and comfort.
See the thermal bypass checklist. and the commentary.

[tucker]

Seems as though for an approach to energy effeciency at a truly affordable level concentrating on the air barrier is a more practical and realistic aproach than designing these high r assemblied that have so much potential for failure and therefore require throwing a bunch of money, materials and skilled labor making these assemblies out of reach for most folks. Don't get me wrong these intricate high-r assemblies are novel and I guess it's got to start somewhere but before folks start calling them "green" they have to be affordable to the masses and not requrie architects, extremely skilled builders, and wealthy owners to make a difference...currently it's not even close.

[steve demetrick]

Allan,
I'm not an expert in this field, but it's all fresh in my brain from 4 days at the JCL show. Insulation and air barriers work together to keep a building energy efficient, each having a separate job working toward the same goal of energy efficiency. Then energy in our conditioned air moves through convection, conduction and radiation. The insulation keeps the energy in the air from moving through conduction, and the air barrier keeps the energy from moving with the air through convection. Some insulations, like spray foams, act as both air barriers and conductive barriers, others, like loose cellulose or fiberglass, act only as convective barriers, but don't perform at an acceptable level to not require an additional air barrier.

-Steve

[Ted S.]

The best information I can find on this is the EPA's Energy Star Guidebooks. The EPA has been way ahead of all this for quite some time:

http://www.energystar.gov/index.cfm?...aining_req#che

I wish I could find the older Version 2.0 Guidebook, although they are rolling out new version of Energy Star, the old Guidebook was much better in detail. ThingofBeauty, you knew about these in one post a while back, do you know the link to the 2.0 book? I just have the downloads which we printed.

I'm actually surprised at the questions on this Thread, I would really recommend reading these books. They helped me tremendously and the thing is, you all currently need to know some of this this stuff under IECC 2009 and even more so under 2012.

I used to do ABAA inspections, it was all commercial. That's some really rigorous stuff, I hope they are not migrating towards residential homes, last I know they had a bubble sucker we'd put on brick ties and suck it down to -75pa and most of them would fail. Pretty hardcore. I hope to get back involved with ABAA if I could ever find the time and now that more commercial is going up.

The short answer Allan is that no, open blown cellulose is not an air barrier according to the EPS's standard. Is dense pack cellulose an air barrier? No, not according to the standard, but it would appear to do a damn fine job in my opinion.

According to the EPS Energy Star Standard:

6. For purposes of this checklist, an air barrier is defined as any durable solid material that blocks air flow between conditioned space and unconditioned space, including necessary sealing to block excessive air flow at edges and seams and adequate support to resist positive and negative pressures without displacement or damage. EPA recommends, but does not require, rigid air barriers. Open-cell or closed-cell foam shall have a finished thickness ≥ 5.5” or 1.5”, respectively, to qualify as an air barrier unless the manufacturer indicates otherwise. If flexible air barriers such as house wrap are used, they shall be fully sealed at all seams and edges and supported using fasteners with caps or heads ≥ 1” diameter unless otherwise indicated by the manufacturer. Flexible air barriers shall not be made of kraft paper, paper-based products, or other materials that are easily torn. If polyethylene is used, its thickness shall be ≥ 6 mil.

Get to know this stuff, IECC 2012 is aligning it's checklist with this language, so I hear, we will know for sure in 13 days.

Any of you vets with this stuff catch the "EPA recommends, but does not require, rigid air barriers."

WTF?

[ThingOfBeauty]

ThingofBeauty, you knew about these in one post a while back, do you know the link to the 2.0 book?

Bill R beat me to it, in post #4:
"See the thermal bypass checklist. and the commentary. " Click on his "commentary" link, it goes to the V. 2.1 TBC Guide.

[David Meiland]

They are willing to allow stuff like Tyvek as an air barrier, or (gasp) even plastic wrap.

[Ted S.]

David, you took the course and everything, is this new? Wasn't only solid materials permitted under the most recent Version 2.0? Where did this come from? There was no mention of nonrigid air barriers permitted in the old guidebook. I am shocked.

[Ted S.]

Yes, thanks that's the good one. But I don't see "EPA recommends, but does not require, rigid air barriers" in that version, only the new version. Up until now it has always been a hard material (or so I thought).

[Dancing Dan]

To go back to the question in #3, yes, Allan, you could have boatloads of loose fill and a crappy air barrier, and get into lots of trouble. We've run into that in attic insulation jobs. If we insulate the attic floor without doing a good air sealing job, all the moisture is still getting through, but less of the heat, so the roof sheathing turns into a condensing surface. Bad scene.

As to which is "more important" - tough call. I guess I'd say insulation without air barrier can cause the building to fail, air barrier without insulation means you're pissing away energy but won't screw up the building in the same way.

[Allan Edwards]

Dan

I am not talking about sealing cracks and penetrations, I am talking about a solid air barrier like you have on walls. Why don't you need the same in an attic?

[Bill Robinson]

Allan, even at the walls there are gaps and cracks unless there is a product in Texas that covers the whole building like a, well like a , well--- a balloon.
Take a look at the abaa specs and you will see it goes from parts and pieces to entire assemblies comprising an envelope.

Capice?

[Dancing Dan]

It's either an air barrier or not. A lot easier to establish in new construction than in reno, so if it's not there you need to pull out the foam guns and caulk. But there's no functional difference - drywall and plaster are good air barriers, it's just the cracks, penetrations and seams you need to worry about.

You would certainly need one in the attic - more so than in the walls, I'd argue.