What Does Air-Sealing An Attic Mean?

You've heard that your attic needs an airtight seal. You've read claims that air-sealing your attic means lower energy costs and a more comfortable home. But what does it really mean to air-seal an attic? If an airtight seal delivers those results, what will it take to get one?

South Central Services has insulated hundreds of homes in and around Greencastle, Pennsylvania. Our team is passionate about air-sealing and seeing air-seals installed correctly.

By the end of this article, you'll understand:

• How to get an air-seal
• The goal of an air-seal in the attic
• What it means to have an effective air-seal
• The benefits of an effective air-seal upstairs

Air-Sealing An Attic Refers To Encapsulation Or Floor Insulation.

No matter where your attic is insulated, you can get an air-seal upstairs. There are two places where your attic can be insulated:

• The underside of the roof and the gables
• The attic floor

Depending on where your attic is insulated and air-sealed, you may or may not have ventilation in your attic. Let's examine what each of these air-sealing options mean in more detail.

1. Encapsulation Cuts Off Your Attic From Ventilation.

If your attic is encapsulated, the underside of the roof and the gables are insulated and air-sealed. The attic is considered part of the conditioned space, so the attic itself does not vent to the outside.

When an attic is encapsulated, the home could have a ventilated roof deck. However, the attic space itself is not open to outdoor air exchange.

2. Floor Insulation Allows Your Attic To Vent Air From Outside.

If your attic floor is insulated, then the floor has an airtight seal and insulation product installed. The attic is not considered part of the conditioned space of the home. That layer of insulation on the floor forms the house's thermal envelope, like a "lid" for the home. Both the attic and the roof deck are open to ventilation.

It doesn't matter if outside air enters an attic with floor insulation, because the air-sealing on the floor stops any air from entering the living space.

The Goal Of Air-Sealing Is To Stop Random Air Leakage.

Whether you insulate the floor or encapsulate the whole attic, the point is to stop air leakage. Whatever part of your home is conditioned (meaning, you pay money for the air in that space) should not be open to random ventilation.

Most attics do not have an air-seal. In fact, the majority of new construction attics we see have either no insulation upstairs or a thin layer of fibrous insulation. Fibrous materials like blown-in and batt cannot air-seal. Air can easily pass through these materials.

An attic can still be insulated with an affordable material like blown-in. However, it must be paired with a separate air-seal. Traditional insulations do not automatically air-seal.

What’s So Bad About Air Leakage?

There's a reason why our team focuses so much on air-sealing. The traditional way of building, which leaves homes open to random air leakage, causes many problems.

When air can randomly leak, your temperatures inside are inconsistent. Air leakage can lead to draftiness in the house as air exchanges. Your HVAC senses the inconsistencies and works harder to make up the differences. A home with no air-seal is less comfortable and less energy efficient.

Not Every Contractor Does Air-Sealing Right.

One of the greatest frustrations about air-sealing is the lack of consistent guidelines or training methods.

If you get a quote from an insulation contractor, you may see a line item for air-sealing. Air-sealing can be a somewhat generic line on these quotes. Despite it being listed, the installer may not deliver an effective air-seal.

We see this often in new construction homes. In our area, houses built in the last 2 to 5 years have insulation failures. On paper, the insulation package looks effective and should be working fine. In application, the system fails.

You could compare this to running your vacuum. In order to actually vacuum up the dirt in your home, you have to pay attention to what you're doing. Running the vacuum over the floor without looking will result in a poorly done job, even with a great vacuum. Often, air-sealing is done "in theory," but the actual results are ineffective.

Working with an insulation contractor who understands air-sealing and will deliver an effective air-seal is vital. Air-sealing is one of the least expensive and most impactful parts of an insulation package when it is done correctly.

An Air-Sealed Attic Is More Energy Efficient.

When you air-seal your attic, you stop the convection of heat in either direction. Hot air cannot press through the attic in the summer or escape through the roof in the winter. Stopping the convection of heat leads to numerous benefits, including:

• More consistent temperatures inside
• Fewer air exchanges in the house
• Increased comfort throughout the year
• Improved energy efficiency

An airtight seal upstairs means saving money on your energy bills, supporting the longevity of your HVAC system, and touching the thermostat less often.

The Bottom Line About Air-Sealing Your Attic

To air-seal your attic, you can either install an air-seal on the attic floor on the underside of the roof. Air-sealing your attic stops convection heat transfer, which makes for lower energy costs and a more comfortable home.

You don't have to use a product like spray foam to air-seal your attic. You can pair an air-sealing method alongside more traditional fibrous insulation like batt or blown-in.

Now that you know what it means to air-seal an attic, your next step is to:

• Learn if you can air-seal your attic yourself
• Estimate the cost of air-sealing your attic
• Discover if your old attic insulation can be reused after air-sealing

Disclaimer: While we strive to publish information accurate to building science, local building codes and standards supersede our recommendations.