Air sealing & Air Barriers 101

Article summary

Air infiltration, building airtightness, indoor air quality and air sealing provide unique challenges for us at Advantage Home Performance. We recognize that if a house has excessive air leakage the house will be uncomfortable and expensive to heat and cool. The other extreme is a house that is too tight and does not have any provision for fresh air ventilation will be more susceptible to indoor air quality problems. This article focusses on homes that are too leaky. For a more in-depth discussion about building airtightness, combustion safety and controlled ventilation, see our article on “Indoor Air Quality”. Our goal, given our customers budget and the realities of a building, is to find the level of building airtightness in which we get the optimal level of comfort, efficiency and indoor air quality.


Measuring building airtightness

A blower door is used to measure a home’s level of airtightness. We can determine fairly quickly if a house is leaky, tight or about right given the size of the house and the number of occupants living in it. The blower door also permits us to calculate the approximate size of the hole that would be created if all the unintentional holes were combined. We use this information to help us determine what solutions would make the house more comfortable, energy efficient, healthy and safe.

Another benefit of using a blower door is that it can lead us to the unintentional holes or air leakage sites. Most homeowners are under the false impression that air leaks around windows and doors. Most homes are full of hidden holes that let conditioned air escape. These same leaks can negatively impact the performance of the insulation. In Arizona, leaks in your attic from plumbing penetrations, electric wires, light fixtures, and building chases that are not capped off represent significant energy losses. Sealing these air leaks is a critical step to improving the overall efficiency and comfort of your home.


Small air leaks

Air sealing work typically consists of sealing up small leak sites with foam. In the photo below you can see where the crew pulled back insulation from top plates and used spray foam to seal the cracks.

Air leakage at top plates of framed interior wall
(Courtesy Saturn Resource Management)
Air sealing of top plates in attic with foam

Our crews seal all plumbing and electrical wiring penetrations. These are the types of leaks that we routinely see as part of air sealing work. In the photo you can see what should happen when this house was constructed. A can of foam with a gun can quickly seal all these small air leaks. Unfortunately these plumbing pipes and electrical penetrations are rarely sealed.

Air sealing with foam gun
Plumbing penetration in top plate: attic view

Larger air leaks – air barrier work

We often deal with larger leak sites where there are no top plates or draft stopping at ceiling height changes. In the two photos below the framer never put in blocking which is called draft stopping. This is a code requirement to prevent the spread of fire, but it also creates convection loops in which warm air in the winter rises up the interior wall cavity and into the attic.

Missing draft stop
Missing draft stop

The solution to these types of problems is straight forward. Our crews cut duct board and insert into the hole with a friction fit. Then they glue air barrier material into place with foam insulation. We refer to this type of work as air barrier work. Once we are done we can blow insulation over the air barrier material.

Missing draft stop
Air barrier work

Recessed light fixtures (cans)

Another example of an air leakage site that is easy to visualize are older recessed light fixtures. These recessed light fixtures can be very leaky. To highlight the problem, I selected two slides taken in attics showing light pouring out of the recessed cans. In the picture on the right when the attic is dark you can see how leaky this recessed light fixture is because light is streaming out of it. Some of these older recessed light fixtures leak like colanders.

Attic view of recessed light fixture
Light streaming out of recessed can in attic

The older recessed light fixtures we see in homes often require the insulation to be kept clear of the fixture by 3”. The problem with recessed light fixtures that require clearance is that they create insulation voids that undermine R-value and as you have seen in the photographs above they are also very leaky.

Recessed light that requires 3” insulation clearance
Air barrier & insulation box for recessed light

Our solution is to entirely air seal and isolate the recessed light fixtures. The boxes we fabricate are constructed out of duct board. The duct board provides both an air barrier and R-value. We don’t have to keep insulation clear of the box we made because the box is insulated and creates the required clearance.


Open chases

Large chases as seen in the photos below with batts laid over them are unacceptable as well. The fiberglass batts are air permeable, air will migrate through via air infiltration and stack effect. Stack effect occurs in the winter when warm air naturally rises like a hot air balloon. These open chases are easily capped with plywood, OSB or duct board. It is not difficult to address these issues.

Large duct work chase in Phoenix home
Large open chase behind fiberglass tub enclosure

Duct leaks

The most problematic air leaks in a home are the ones in the air distribution system. Duct leaks have a big impact on utility bills and indoor air quality. The leaks garner a lot of attention because when the air handler fan is running these leaks see the highest pressures. In the photo below on the left side you can see a big return leak which is sucking hot dusty air right out of the attic. In the picture on the right hand side we see a disconnected supply duct which means this customer is cooling their attic. This is why the utilities have special rebates for sealing ductwork. We dedicate a special section of this website to duct leakage.

Large return duct leak in Phoenix home.
Disconnected supply duct in attic

Spray foam

Insulating a house attic with spray polyurethane foam (SPF) insulation on the underside of the roof deck is the best way in almost all cases to insulate and air seal an attic. This is especially true if the air distribution system (duct system) is located in the house attic. The benefits of an unvented attic with cathedralized foam insulation are numerous; more energy efficient, noticeably less dusty, much quieter and fewer insects. The downside of this approach is cost. Unfortunately, it is very expensive to remove existing insulation and then to insulate with spray polyurethane foam. For more information about this approach see our article “Spray Foam Insulation for existing homes.”


Building airtightness & indoor air quality

We adopt four strategies when performing air sealing work in our customer’s homes to help ensure that we don’t compromise indoor air quality. The first is to address potential indoor air quality problems beginning any work. We look for potential combustion safety issues as a result of air sealing and duct sealing. We look for source control issues like kitchen fans that don’t vent to the outdoors, scented candles, damp crawl space or anything else out of the ordinary.

The second strategy is to encourage the use of fresh air ventilation systems. If we are going to install a fresh air ventilation system in a house then we seal the house as tight as we can. Fresh air systems can be simple and relatively inexpensive and they can also be sophisticated and provide state-of the-art air filtration of incoming fresh air before it goes through the heat exchanger. When economy is important we use an upgraded the bathroom fan to a Panasonic fan that can be run at a very low speed 24/7. We also install fresh air ventilation systems with HEPA filtration on the for customers who are concerned about allergies.

The third strategy is customer education. Articles like this are designed to help motivated customers decide what they want to achieve in their homes. Our belief is that good information drives the decision making process.

The fourth approach is not to perform air sealing if the customer is only interested in insulation. We are happy to do this. This is what happens in the marketplace every day with almost all insulation companies. Our goal is to give customers options. We also are not interested in doing mediocre work. We are not interested in blowing more insulation in an attic when what the house really needs is air sealing and air barrier work.


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