Understanding Air Sealing Strategies


Air-flow, air-sealing, air-leakage, air barriers—inside, outside and everything in-between—is there really a whole house solution for today’s builders and contractors?

circle-chartIf you were thinking yes, then I am sorry to disappoint, but the short answer is no; there is not one single solution that can meet the needs of every building.

Just like building science, any good air sealing strategy begins by recognizing that the building envelope is a series of interrelated systems, parts and components and it must consider the relationship between each of these along with environment.  We cannot think about air without also thinking about the flow of moisture through a building component or how heat is transmitting through the wall (whether it is coming from the inside or the outside).  It is also about anticipating failures before they occur…as opposed to addressing them after they happen.  It is a balance—and in some cases—it is also a compromise between each of these fundamental principles.
So…with that in mind…let’s talk about air.  It is referenced in many ways—leakage, sealing, barriers, flow—but at the root of it…what is it really about?  Why should it matter to you?  Well, put simply, it is about control.  We want to control the air—keep the inside air in and the outside air out.  A home is comprised of a bunch of tiny holes, gaps and openings that all add up to much bigger holes which can make achieving control much more challenging.  In some cases we look at it from the standpoint of separate and distinct layers (e.g. air control layer, water control layer, etc.); however, I prefer to look at from a bit broader perspective and divide it into two distinct categories:

  • Interior Air Barrier Strategic Solutions
  • Exterior Air Barrier Strategic Solutions

Exterior Air Barriers have the added challenge of providing a weather barrier behind the exterior cladding while also protecting the interior components of the wall.  Interior Air Barriers have the challenge of addressing inconsistent wall continuity between floors and other discontinuous components.  And while there are pros and cons for both approaches, they are both necessary to truly address the needs of today’s buildings and there are multiple tools, products, systems and even trades who need to work together to ensure success.  A leaky structure can compromise an entire building envelope, and air tightness has a tremendous effect on every other performance aspect for how an occupant experiences a building.  These effects include:

  • Overall comfort
  • Indoor air quality (IAQ)
  • Energy efficiency.

exterior-vs-interiorLet’s first look at the two primary functions these materials must provide:

  1. a vapor-permeable layer that allows moisture trapped in the wall to escape.
  2. an energy-efficient air barrier that stops air infiltration and exfiltration through the wall.

So what?  How can an “air barrier” product be an air barrier if we poke a bunch of tiny holes in it to get it to stay on a wall (or in the case of windows and doors…really, really big holes)?  Or wait, we have a roof that sits on top of these walls, but isn’t even integrated into the wall air barrier so we let all the air leak up through the ceiling and roof…which gets back to our original point—there is no one single solution.  The only single solution is to use a combination of products to create a system that addresses both the exterior and interior side of the wall.

Exterior Air Barrier Strategies employ products like fluid-applied membranes, water-resistive barriers and insulation boards.  Combining these systems with tapes and joint sealants is a great way to address the leakage paths on the exterior side of the wall.

Interior Air Barrier Strategies also include a variety of solutions.  Spray Polyurethane Foam can be used to address challenging details (e.g. rim joists) or with hybrid applications in more cost-conscience jobs.   It can also be utilized as a full-cavity solution or in conditioned attic assemblies where mechanical equipment may be in the attic.  Air-tight drywall, window foam sealants and caulk & seal packages can also be great solutions to address a variety of details from the inside.  Newer, more-advanced approaches also include using a smart vapor retarder installed as a continuous air barrier with tapes and sealants or you could utilize a similar system that is integrated with batt insulation that can be simply taped to tackle air, moisture and heat in one application.

inside-lookAnother interesting nuance is that exterior systems also generally involve exterior trades (framers, siders, etc.) and interior strategies generally involve interior trades (insulators, drywallers, etc.).  But you must ask yourself who generally is responsible for the occupants comfort, indoor air quality or energy efficiency?  Regardless of whether your responsibility lies on the inside, on the outside or both, you must make sure that you are utilizing the strategies above; otherwise, you might be letting out a bunch of hot air instead of keeping it under control.

1 Comment

  1. Isn’t caulking and sealing framing from the inside really saying you are okay with allowing air to deplete insulation values lost from air entering the insulation cavity from the outside? Caulking and sealing framing from the inside does little. You need to do both inside and outside to stop air.

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