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Exterior, mid-wall, or interior? Where do you put your air barrier for the best results?

A critical aspect of efficient air barriers is that they have no holes or disconnections. If you’ve read our journal, you’ll note that we sing the ‘continuous’ melody over and over again. The only way to ensure continuity is to decide where the air barrier will rest inside the wall assembly ‘sandwich’ early on.

While there are several wall construction options, most of them share the same physical elements – interior finish, structure, insulation, secondary drainage plane, and cladding.

Since one of the goals of the air barrier is to promote effective temperature regulation eventually, we often choose where to plug in the air barrier with the thermal layer. So, like any novel, the air barrier has a beginning, center, and end – it may be on the outside, inside, or somewhere in-between the wall insulation.

In this post, we will simplify the process of identifying the air barrier. We’ll even send you some pros and cons to help you decide what’s suitable for your idea.

1: Exterior air barrier

What exactly do we expect when we say “outside”? Anything that is not inside the thermal layer. This is the most popular air barrier form, and it often uses the secondary drainage plane as a piggyback.

Technically, we could include wall cladding as an exterior alternative. Still, even with a “continuous” cladding like stucco, there are control joints, cracks, and transformations that simply cannot effectively seal the building from air infiltration. That will be an extremely time-consuming implementation with much more time-consuming maintenance. In this situation, the air barrier needs to be hidden ‘inside the outside.’

This is usually seen in a code-minimum building, with differing degrees of efficacy depending on the project’s specific performance requirements.


  • Essentially the same wall and materials that designers are now familiar with. Minimal new preparation is expected to complete the task.
  • Cost-effective – Using a current layer eliminates the need for an additional pass across the structure.
  • Accessible to QC and locate problem areas, as well as to enable blower-door checking during building.
  • As compared to the interior solution, there are fewer penetrations.

2: Mid-wall air barrier

This is just as the name implies – The air barrier is sandwiched between the thermal layer of the wall. Because of our widespread use of continuous insulation (CI), this is the second-most common position for an air barrier.

CI puts an additional blanket of insulation around the entire structure’s exterior, designed to minimize thermal bridging but is not necessarily intended to satisfy the building’s maximum insulation requirements. After that, the mid-wall air barrier is installed between the two layers of insulation. May make it with a wholly insulated weather shield, plastic padding, or taped sheathing.

Another case in point is the possibility of an air-tight layer inside a double-stud wall assembly. You may also use the old-school passive house system of installing an air-tight sheet under TJI or Larsen truss outriggers of insulation outside the mainframe.


  • Safeguarded against damage both before and after construction
  • Uses existing building layers

3: Interior air barrier

The air barrier is entirely on the warm side of the insulation in this situation. There isn’t anything between the edge of a stud and the finished paint: a coating of gyp and maybe a vapour retarder.

In a perfect world, must construct the air barrier with a wholly enclosed vapour retarder and a service cavity separating it from the gyp to reduce the number of penetrations from MEP trades.

Another example is an ‘economy’ variant of the air-tight drywall method. This method depends on caulk along the perimeter of the wall and sprays foam at penetrations. It’s common in high-performance retrofit projects where the exterior is left intact, but the interior is uncovered and in mass wall construction.


  • Controlling the thermal volume on the warm side contributes to optimum construction physics.
  • Works well in situations where outside access is impossible or troublesome and for separate spaces within a broader structure.
  • There is little chance of UV and weather damage, and it is usually built after the building has been dried in.

Air barrier solutions

Is it possible for me to have two air barriers?

Well, yes! However, it is not always necessary, and you should always determine the condensation risk based on your particular environment. This is most effective in warmer temperatures and programs aiming for passive house airtightness.

What would give me the best airtightness result?

All are subject to the limitations of tradespeople’s ability levels, code and project success criteria, environmental conditions, and building sequencing.

It is all about constructability and teamwork when designing an air barrier into the assembly. Identifying the project air barrier priorities early on and then addressing build and expense problems with the contractor as the project continues would help achieve a great result.

We Got You Covered to provide water and fluid-applied air barrier protection designed for the unique demands of heavy construction projects.

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