Why Is Air-Sealing A Home Important?

You're thinking about upgrading your insulation. You could install fiberglass, which insulates. Or, you could install spray foam, which insulates and can provide an air barrier. Do you really need an insulation that air-seals? Will it be worth the investment?

We understand why you may be concerned. Thirty years ago, air-sealing was relatively unheard of in most construction. Now, building science has improved, and insulation has improved along with it.

Investing in an air-seal may be optional for your project. But as professionals with years of experience in insulation and HVAC, we want to teach you why air-sealing is becoming a standard in energy-efficient buildings today.

By the end of this article, you will know:

• What air-sealing is
• What benefits air-sealing can provide
• How to test for air leaks
• How to get an air-seal in your home
• Problems that can arise related to air-sealing

Don't have time to read right now? Check out everything you need to know at a glance.

What Is Air-Sealing?

Traditionally, buildings ventilated air through air infiltration, natural ventilation, and mechanical ventilation. Air infiltration is random air leakage through structural gaps, while natural and mechanical ventilation can be controlled. All three ventilation methods are part of the standard design in older homes.

Air-sealing, also known as an air barrier, prevents ventilation through air infiltration. An air barrier seals cavities or gaps in a building’s structure to prevent air leakage in or out of the building.

Air-sealing will not prevent natural or mechanical ventilation but will stop random air leakage.

How Are Air-Sealing And Insulation Related?

Warm air is drawn to cold air, directly impacting homes and their conditioned air. In the summertime, the cool inside air attracts heat from the outside. In the wintertime, the cold outside air tempts heated inside air to escape the home.

Any time air exits the home, an equal amount of air enters the home. There is always an exchange of air. For homes without an air-seal, expensive conditioned air will exchange with unconditioned outside air. This exchange will include temperature differences and possible outdoor air pollution.

When building a structure, it is best practice to first air-seal and then insulate. The insulation and HVAC system of a building functions more efficiently when a foundational air-seal exists.

You can compare this principle to an insulated thermos. If you use a thermos to keep a drink hot, you will screw an air-sealing lid onto the thermos first before adding the cap. The thermos may also have two walls to help insulate the liquid.

However, the element contributing most to keeping your drink hot is the air-sealing lid. If you used the thermos without this air-sealing lid, the insulated walls would not keep the drink hot for nearly as long.

In a building, an air-seal helps conditioned air to stay inside. Whether it’s cool air in the summertime or warm air in the winter, air-sealing supports the insulation and HVAC.

What Are The Benefits Of Air-Sealing?

We’ve established that air-sealing is a legitimate feature backed by building science. But what measurable benefits can air-sealing offer? There are four significant perks of air-sealing.

1. Energy efficiency cost savings
2. Air quality control
3. Increased comfort in the home
4. Less HVAC wear and tear

Let's examine each of these in more detail.

1. Air-Sealing Makes Homes More Energy Efficient.

We pay to condition the air in our homes. If it’s hot outside, we pay to keep it cool. If it’s cold outside, we pay to stay warm. The temperature-controlled air from our HVAC systems is expensive.

Air-sealing not only increases energy efficiency but also saves money. In an air-sealed house, conditioned air cannot escape uncontrolled. Instead of paying for more energy to compensate for lost conditioned air, you only pay for the energy that your home needs.

2. Air-Sealing Improves Indoor Air Quality.

When we think of fresh air, we may think of a refreshing deep breath. Driving past a farm with the windows rolled down is also an example of fresh air, although taking a deep breath is far from refreshing.

When air leaks uncontrolled, that fresh air can bring allergens, dirt, and dust with it. With air-sealing, you can prevent outdoor air pollution from leaking into your home. The air that mechanically ventilates inside is a breath of fresh, filtered air. Spray foam insulation, with the right HVAC equipment support, can improve indoor air quality.

3. Air-Sealing Increases Comfort In The Home.

You may not realize that your home is uncomfortable. Many people get used to the discomfort in their home.

When the weather turns cold, they get out more blankets and bump up their thermostats. Once summer arrives, the house is hot and sticky. It can be too hot to sleep without a ceiling fan running on high.

Whether it's a draft and cold floors in the winter or stifling heat in the summer, many HVAC systems struggle to maintain a comfortable living environment.

Air leakage is the primary cause of temperature changes and drafts. 

By air-sealing, homes can eliminate these discomfort issues. Basement and crawl space insulation can address drafty cold floors. Attic insulation can prevent excessive heat from pressing into your living space.

An air-sealed home will have consistent temperatures and eliminate the drafty feel.

4. Air-Sealing Supports HVAC Systems For Less Wear And Tear.

The HVAC system is responsible for maintaining indoor air climate, which includes temperature and humidity. Uncontrolled air leakage introduces random temperature fluctuations that the HVAC must handle. These temperature changes increase the strain on your HVAC system.

Many attics have HVAC vents running through them. Without an airtight seal, hot air leaks into the attic.

The disparity between the attic temperature and the air in the vents can be as high as 100 degrees. That is an incredible amount of heat load that ductwork often absorbs, forcing the HVAC to work harder.

Air-sealing supports the HVAC by eliminating the potential for temperature changes due to air infiltration. By restricting uncontrolled temperature exchange in the house, an airtight seal limits the overall wear on the HVAC equipment.

How Do I Find Where Air Is Leaking From?

Air commonly leaks from windows, doors, chimneys, exterior walls, and attics. Where air leakage occurs will vary in every house.

A blower door test is one way to determine where air is leaking from in your home. Depending on the weather or climate, contractors may be able to diagnose air leakage areas with just a thermal camera.

I Want An Air-Sealed Home. How Do I Get An Air-Seal?

Many products exist specifically for air-sealing. In new construction homes, adhesive building wraps are sometimes used as an air-sealing product. Remodel jobs could benefit from products like siliconized spray or liquid-applied air barriers. Even caulking, in specific applications, can help to create an air-seal.

Spray foam insulation is a product that can both air-seal and insulate. Both types of spray foam, closed cell and open cell, can air-seal. For homes needing an air barrier and improved insulation, spray foam can deliver both needs.

Most insulation products do not air-seal. Fiberglass and loose fill cellulose insulation are popular materials that cannot stop air from leaking into or out of a home. Those insulations insulate by allowing air to pass through them. While you could pair one of these insulations with an air barrier product, spray foam can solve both issues with its application.

Are There Problems With Air-Sealing?

Air-sealing is the first step to controlling air quality in your home. An air barrier can support the insulation and HVAC system. However, to achieve ideal mechanical ventilation, other steps must be taken.

Building an efficient home requires many contractors with specialized skills who work together. HVAC contractors must consider air-sealing and insulation when recommending an HVAC system. In the case of spray foam insulation, the air barrier will directly impact the HVAC. Problems can arise if the home systems are not working together.

Another step in controlling the air quality in your home is investing in a heat recovery ventilator (HRV) or energy recovery ventilator (ERV). These machines can help process the heat and moisture from outdoor air as it exchanges with stale air from the home. HVAC contractors can advise you if these systems will benefit the air quality in your home.

The Bottom Line About Why Air-Sealing Matters

Buildings without air-sealing exist. Before the advancement of building science, every building was open to random ventilation.

Homes can exist without air-sealing. However, as contractors with experience in both HVAC and insulation, we recommend considering an airtight seal. Without an airtight seal, HVAC systems struggle to maintain a comfortable home environment. Air-sealing can improve your indoor air quality, energy efficiency, and home comfort, as well as preserve the lifespan of your HVAC equipment.

Now that you understand why an airtight seal matters, your next step is to:

• Compare spray foam insulation to fiberglass
• Weigh the pros and cons of spray foam insulation
• Estimate the cost of encapsulating your attic