A well-designed air barrier is a foundational piece of achieving a comfortable, energy-efficient building. Yet adding an air barrier into a project is not necessarily a given. The air barrier layer is definitely a newer trend in our understanding of how to make buildings that work – it wasn’t even included in the IECC until 2009.
Builders are still learning ways of integrating a continuous air barrier into a project. Strategies have evolved though: currently air barriers typically end up on the exterior, through continuous sealing of the weather-resistive barrier (WRB) or exterior sheathing. Previous trials used an interior drywall approach or sealed poly and (before we knew better) a spray foam-heavy approach.
As you might expect, our European counterparts have been at this a little longer. But how much of the European’s air barrier methods are relatable to how we do things in America?
Let’s dig into some differences and you can decide.
1) The air barrier is usually on the interior. So is the sheathing
European framing methods are reversed from ours — sheathing is often on the interior face of framing and insulation applied from the outside. This is often due to usage of higher-quality timbers vs dimensional lumber.
Some of the first effective techniques from 30+ years ago used a tape sheathing layer to achieve an air barrier. And in Europe, this was found on the inside. European OSB is also usually higher quality and offered in larger dimensions, both of which further supports its use as the air barrier.
In addition to this, from a building science standpoint, the air barrier is also responsible for avoiding moisture transport through convection or air leakages. Therefore, many Europeans prefer to deal with moisture-transport related topics like vapor barrier and air barrier on the inside of the wall where the moisture is generated. The European framing model effectively kills two birds with one stone, as the OSB takes over the function of vapor barrier and air barrier at the same time.
Due to the low permeability of sheathing materials like OSB or plywood, the more ideal location for these materials is on the interior as in heating-dominated climates vapor transport is directed toward the exterior for most of the year. This promotes more effective drying and mitigates the risk of building damage.
2) Mass-wall construction is far more common
From Italy, to Germany, to the UK, masonry block walls (hollow terra-cotta) with timber-framed roofs are very common. Historically, pre-industrial construction methods in both US and Europe ‘worked’ due to their simplicity and construction with legacy materials. They leaked a lot of air (and water, actually) but it didn’t matter because energy was cheap. Our understanding of and contributions to industrialized pollution was far less, so the motivation to change wasn’t quite there yet.
Now we need to conserve energy while increasing comfort and reliability (read: create air barriers). In a mass wall, an air barrier is detailed on the interior due to the ability to directly plaster the interior and tendency to insulate the exterior.
3) It’s the service cavity, baby!
Use of a service cavity in walls is much more common in Europe – also due to #2 above. The most relevant US equivalent would be a dropped ceiling, but this technique is rarely used in walls.
The basic concept is to use sleepers (aka: furring, strapping or standoffs) to create a physical separation between a finished material and a hidden barrier layer (of any type). This allows the barrier layer to be detailed properly. It also provides a more efficient insulation layer because there are no interruptions by mechanical systems.
4) They have awesome windows, and know how to use them
Tilt-turn, block-style windows are also commonplace, again due in large part to mass-wall construction. By design, these windows seal much tighter, both mechanically but also in how they are installed. Sealant or tape flashing is used around the entire perimeter (including the sill), which creates a de facto air barrier. Moisture can escape through weep channels built into the frame.
A typical North American flanged window is only sealed on 3 sides to allow an exit path for moisture at the sill. This exit path also happens to allow for air leakage. As a result, air-sealing a flanged window properly requires a separate step — which doesn’t always happen.
Additionally, tilt-turn windows do a great job of allowing natural ventilation, which might help address the fact that…
5) … We’re afraid of stale air (and 6mil poly)
Building a tight home can be intimidating at first. Air barriers create some unfamiliar variables, such as how to circulate fresh air, managing temperature properly and dialing new mechanical systems.
Many regions in the US and Canada have also experienced horror stories of mismanaged moisture due to 6-mil poly. Back in the 70s, polyethylene sheeting wasn’t exactly intended as an air barrier, but rather as a newfangled version of a vapor retarder. And some builders still use it that way today. Air barriers get a bad rap by proxy because the methods and placement in the wall are similar.
6) The trades command higher respect, culturally
It’s not a slight on the talents of our tradespeople, but developing quality skills and legitimate career paths for skilled laborers more often than not relies on private businesses in the US. Even in states where trades are unionized, it’s also not necessarily viewed as a trusty long-term career path.
In contrast, many European countries have extensive apprenticeship programs that begin at a young age which are tied to well-established businesses.
According to Tobias Eberwein, an Application Engineer for SIGA originally from Germany and now based in Vancouver, apprenticeship programs are generally led through recognized local businesses. The programs provide a combination of work under an experienced master tradesman and specialized trade school where the status-quo of each trade is taught. These programs in average last about 2-3 years whereas practical knowledge and skill transfer are key.
After this base apprenticeship is concluded there is the option of pursuing a master tradesman program or even a technical degree. Many practicing engineers in central Europe have trade backgrounds, which massively benefits the communication and mutual understanding on site which is a driver for innovation.
How does this tie back to air barriers? Because air barrier construction is a newer skill in the US, there isn’t always uniformity in the knowledge being passed on, or even a clear path of where to go to get this knowledge. European systems where a higher volume of young people are being trained with the most up-to-date knowledge, brings new skills to the mainstream (like air barrier techniques) much faster.
There are certainly different construction methods between Europe and North America. Yet it may be the cultural + economic differences which factor into how newer technologies like air barriers get designed and adapted.
If you’re looking to up your build skill and learn practical steps for building air and weathertight, visit our training page. SIGA offers webinars, eBooks and the opportunity to attend academies and workshops.