An Air Barrier Is NOT a Product
Professor John Straube is one of the smartest guys in building science. On top of that, I think he’s the best presenter in the field. At the Air Barrier Association conference in Baltimore, he gave one of the best building science talks I’ve heard. Of the things he said, this statement really stood out:
“There’s no such thing as an air barrier product you can purchase. There are only air barrier systems that have to be assembled.”
The photo above is not an example of a well-assembled air barrier system. In fact, it illustrates Professor Straube’s point. Whoever did this used several products that individually are good at stopping air leakage. A little inspection, however, shows that the system they assembled has some flaws.
There are a lot of great products out there that can help make a building airtight: structural insulated panels (SIPs); air-sealing tapes from Siga and Pro Clima; spray foam insulation; Huber’s Zip sheathing (disclosure: they advertise here); liquid-applied WRBs like Prosoco’s R-Guard and Sto’s StoGuard; and self-adhered membrane’s like Cosella-Dörken’s Delta Vent SA or Henry’s BlueSkin VP100.
But not a single air barrier product on the market can ensure you have an airtight building if you use it. Yes, you’ve got to use good products, and the more airtight you want the building, the more important that is.
The products you use, however, are only part of the whole system. As with most things, the devil’s in the details. You’ve got to install those products correctly. You’ve got to use the right product in the right place. And you’ve especially got to watch out for transitions and penetrations.
An air barrier is a system. Not a product.
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Does Your Air Barrier Work in Both Directions?
Photo credit: Although it looks like something I might have found during the bathroom remodel I’m doing at my condo, my friends at Mechanical Hub posted this on Twitter recently. It is used here with their permission.
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After 41years in the energy
After 41years in the energy conservation contracting business, I am not naturally detailed oriented, but I do believe for building science it is important. And I believe the saying should be “God” is in the details, not the “devil”. Thanks for sharing all the details, with all of us…”sharing and caring” all these years…cheers!
Hmmm. I hadn’t thought about
Hmmm. I hadn’t thought about it that way before, Dennis, but I guess you could see it either way.
As a registered architect and
As a registered architect and after decades of specifically dealing with forensics of all types and ages of buildings, I agree with the remarks by Pro. Straube about AB systems have always been true, not only for Air-leakage, but always for every system of each part (trade) in construction.
Yes, indeed, Thomas. We
Yes, indeed, Thomas. We preach the house-as-a-system here all the time.
Great post and point as
Great post and point as always. So a question I hope many are asking in reading this- if no product in isolation can be considered an air barrier without being part of a larger system, why do so many model codes and standards allow air barrier compliance via a material test (ASTM E2178) in lieu of a system test (ASTM E2457) and either in the absence of a whole building air leakage performance verification (ASTM E779 + USACE or similar)?
Great question, Keith.
Great question, Keith. Fortunately, more and more state and local building codes are requiring blower door tests.
AMEN! to this whole post and
AMEN! to this whole post and especially the title. On a similar note: many new builder clients of mine often tell me, “My insulation contractor included the air-sealing package in my bid” and consider it done. Great air-sealing starts in the design phase and often affects the framer and can affect other trades as well. It’s important for us to help educate the industry to the fact that great air-sealing can’t be purchased via a single line item on a bid.
Good point, Ryan. If it’s not
Good point, Ryan. If it’s not tested, air sealing doesn’t mean a whole lot.
Dear Sir, I was lucky enough
Dear Sir, I was lucky enough to have joined linkedin a few years back and signed up for RESNET among many others involved in building science. While not obvious at first, that simple move has broadened my knowledge tenfold over the career training that I have completed. There is no such thing as TMI when it comes to building science. Not to get to far off subject but the word “system” had not really hit home until I read your short piece. You have a way of drawing me in with your light hearted titles and writing style that gets my brain churning. So much so that I was hungrily catching up on some related articles from 2011. Flat or lumpy? Attic pull down stairs etc.. You were right, I WAS blown away!! So much so that I forwarded the article to my work email to share with some seasoned colleagues. I’m being generous calling them that and I was received with utter contempt. They argued that the average u value was a farce and YOU must have had your math wrong. One even hen pecked his calculator and came up with an entirely different number. He has hands only a mother could love. Me being a former math geek helped him find his mistake. He was stressing the decimals down to the 10 thousandths. Stupid fingers. The other argued that there is an equation on the web that proves 2+2=5 which he printed out and threw on my desk. He is especially pompous. Sorry to say your PhD in Physics was a waste. I argued in vain that it was a simple equation to achieve an average NOT rocket science. The hard part comes later when you tie that in with the principle of “conductive loss”? Still have more studying/digesting to do on my end. Thankfully, I am a big fan of diving in deep when it comes to theory and you sure do deliver. Anyhoo, I re-audited (WAP) a house that I originally audited three years ago for a sister program (NYSERDA) and found some things I missed, some things we did well and didnt do well. It was nice to have a second chance with a much improved skill set. Bill model showed some improvement but not the home run I was hoping for. Found the foam dome over the pull down attic stairs in pieces up in the attic. Couldnt believe that I hadnt called for a zip cover in addition to the foam dome. Talk about timing. I just learned that the pull down is a “mind blowing” part of the attic insulation “system”, got shot down by the hard heads in my office and end up back at this house the very next day. This is going to be fun!! Zone 4 here and lots of test data and usage info if you’re interested. Looking forward to my next email alert from RESNET. Thanks for all you do!! You are my hero. Best Regards, Peter Newton from upstate NY.
Thanks for the kind words,
Thanks for the kind words, Peter. I’m glad you’ve found this stuff useful and that you’ve taken advantage of the list of Related Articles I always include at the bottom of each post. Be careful though. Learning building science can become an obsession!
Because of the preponderance
Because of the preponderance of stick built buildings in this country, I find these types of discussions always focus upon products needed to seal an inherently leaky type of construction. I would submit to all that a better way to reduce the problem is to choose a better type of construction and that would a more monolithic type. There three primary ones to choose from (IMHO): ICF insulated concrete forms, SIPs structural insulated panels and Superior Walls precast insulated concrete panels. These three systems virtually eliminate air leakage within the wall system (windows and doors still can be a problem). For my company, we have done a fairly detailed comparison of the three and have chosen to build only with the Superior Wall product. This eliminates the need for all of these additional products (I would use the term bandaids but that could be construed as being derogatory).
Best pieces of advice I can
Best pieces of advice I can give people who create efficiency specifications or manage people who install the installation of efficiency specifications are as follows:
1.) Get out of the office
2.) Get in the field
3.) Install said product or system you are recommending or watch said product or system being insatlled
You will never fully understand the detail you are creating or attempting to execute until you try it yourself.
Every assembly is different. Every building system (Sitck, ICF, SIP etc) require additional foams, sealants or tapes to “seal the deal”. Depending on the building system and the age determines which types of foams, sealants or tapes should be used. No silver bullets, no one size fits all. I’ve seen good details, I’ve seen bad details. Energy efficiency and the evolution of this county’s use of building energy will happen in the field, in the dark hot attics and musty crawl spaces. It will not happen drawing details in offices.
Excellent point! That’s one
Excellent point! That’s one of the best comments I’ve ever received here, John.
Another way to look at this:
Another way to look at this: AFTER a home is air sealed, work done by any subsequent contractor can DESTROY it. My 1960 ranch in upstate NY was completely air sealed and insulated and performing well. Now I am getting estimates to renovate the master bath and replace the tub. Had a plumbing contractor lined up; when I mentioned the home had been air sealed (including the plumbing entry for the tub from the basement), that I expected them to understand what that was, and replace whatever they disturbed, they pulled out. Why aren’t ALL TRADES fully on board?
Their is an exception to your
Their is an exception to your article. AccuFrame Energy Seal is a new product the conversation of air sealing. So effective it reduces air infiltration by over 80% in stick framed walls. How, a integrated approach to installing the AccuFrame gasket between the OSB sheathing and the framing. AccuFrame comes with pre-printed 16″ OC marks so the framer receives quality control, productivity. The air barrier industry is changing for the better towards a common since solution to energy performance in stick-framing. The sandwiched gasket also has early data suggesting it makes the wall stronger through Coefficient of friction.
watched 60 Minutes two nights
watched 60 Minutes two nights ago … artwork as above was fetching astronomical prices … Sotheby’s?