The Sealed guide to air sealing

What is air sealing? Why is it necessary? And is it safe? Get to know this vital but often overlooked home improvement.

What is air sealing? Why is it necessary? And is it safe? Get to know this vital but often overlooked home improvement.

Along with insulation, air sealing is one of the most important things you can do to improve your home’s comfort and energy efficiency. 

Air sealing regulates airflow throughout the home, keeping your house less stuffy in summer and reducing drafts in winter. It can also improve your home’s overall air quality, reduce humidity, and cut back on the amount of energy consumed by your heating and cooling equipment. 

Despite its many benefits, we’ve found through years of conversations with thousands of homeowners that many people don’t know about the impact that air sealing can make. Some have never heard of it. Others worry too much air sealing will make their house stuffy or even unsafe. 

In this article, we’ll address some of the questions we hear most often about air sealing, and even debunk a few myths along the way. 

Why air seal? A house needs to breathe, right?

Every house needs healthy airflow. 

Natural airflow helps prevent the buildup of mold and mildew throughout the house, and mechanical airflow (like the vent from your furnace) prevents unwanted and sometimes dangerous air from remaining trapped in your house.

Many houses exchange air at 3-4 times the rate that is necessary

Sealed home energy audit data

The trouble is that many houses, especially older ones, have problems with excess airflow. Gaps and cracks in your foundation, attic, and walls joists create little pathways for air to travel through. Individually, these holes might be tiny—maybe the size of a dime or even smaller—but they add up to a big problem. We’ve found through our audits of thousands of homes that many houses exchange air at 3-4 times the rate that is necessary: it’s like having an extra window open in your house 365 days a year. 

Air sealing solves the problem of excess airflow, to ensure your house has the air it needs to keep you healthy and comfortable.

Where to air seal?

When applying air sealing, we primarily focus on two areas of the home: the foundation and attic.


As your home ages, small gaps and crevices begin to develop in and around your foundation. These openings, which are a prime source of excess air flow, are one of the first areas when air sealing a home. We also seal the wooden beam around the perimeter of your foundation so it’s protected from unwanted air entry. 


Duct work, electrical wiring, plumbing, and even recessed lighting fixtures create pathways for unwanted airflow. Using expanding spray foam sealant, we’re able to plug these holes so excess air can no longer pass through. For recessed lighting, the fixtures are capped from above with fire retardant boxes, and sealed around the edges.

Other areas

Leaky windows and doors can also be a source of excess airflow, especially in older homes. We tackle this problem with another form of air sealing: weather stripping. It’s a quick, easy install, and far more cost-effective than replacing the windows and doors. 

Maintaining proper air circulation

Some homeowners worry that air sealing can make their house too stuffy, or prevent the flow of healthy air throughout the home. In the home performance industry, this problem is known as “over-tightening.” 

While over-tightening is definitely something to be avoided, we’ve found that it is rarely, if ever, an issue with the homes Sealed services. 


Rather than causing stuffiness, air sealing prevents it. Without air sealing, warm, humid air can be drawn into the house in summer. In winter, a house without proper air sealing can be freezing on the first floor, and an inferno upstairs. 

Too little airflow

Houses built very recently, with a lot of insulation and air sealing already in place, are at risk of over-tightening. So are houses that lack proper mechanical ventilation. However, houses built in the 20th century or earlier often have so much excess airflow that there is plenty of opportunity to air seal while maintaining healthy airflow.

But you don’t just have to take our word for this. The Building Performance Institute, the governing body that certifies the home performance contractors we use at Sealed, has clear guidelines and mathematical formulas for preventing over-tightening with air sealing. We follow these standards on every project at Sealed. 

Air sealing and insulation: a powerful combination

Air sealing and insulation work best when they work together. Insulation works like the down lining in a winter coat, helping lock in warmth, and air sealing is like a wind breaker, stopping excess airflow. 

If your house is heavily insulated but lacks proper air sealing, your insulation won’t have the same weather-stopping power. Plus, having a lot of insulation without proper air sealing can create secondary problems like mold and mildew buildup. Air sealing acts as a natural moisture barrier, and can prevent these problems as well. 

Go with the pros

Air sealing is highly specialized work. To be done properly, it requires in-depth knowledge of the way air moves through homes. It also takes time and persistence—it’s a lot of hard work finding and plugging all those little holes!

That’s why Sealed only works with certified home performance contractors. Together we evaluate your house as an ecosystem in which all parts are connected. Certified home performance contractors are the only people we’d trust with the important work—and they’re the folks we’d recommend even if you choose not to work with Sealed.

Want to learn more about air sealing? Think your house might be too air leaky? We’d be happy to help. Give us a call at 888-985-7481 to speak with one of our experts.

February 24, 2020