How to Properly Seal Window Gaps to Prevent Air Infiltration in a New Home

Air infiltration is one of the leading causes of energy loss in homes, especially around windows and doors. If these areas aren’t properly sealed during construction, they can lead to drafts, moisture problems, and increased heating and cooling costs. One of the most effective ways to eliminate air leaks is by using low-expansion canned foam around window openings. In this guide, we’ll walk through the correct way to install canned foam around a window to ensure a complete air seal and maximize energy efficiency in your home.

The Problem with Fiberglass Insulation for Window Gaps

When installing windows in new construction, there’s often a small gap—typically about ¼ inch to ½ inch—between the window frame and the surrounding wall framing. Many builders and homeowners make the mistake of stuffing this space with fiberglass insulation, thinking it will prevent drafts.

However, fiberglass insulation is not an air barrier. No matter how tightly it’s packed into the gap, air can still pass through it. Over time, this can lead to significant energy loss and uncomfortable drafts inside the home. Instead of relying on fiberglass, using a proper air-sealing method like canned foam is the best way to ensure an airtight seal.

Using Window and Door Foam for Proper Air Sealing

To correctly seal the gap around a window, you’ll need a low-expansion window and door foam. Unlike standard expanding foam, which can exert too much pressure and potentially warp or damage window frames, window and door foam expands just enough to fill gaps without causing any structural issues.

Here’s the step-by-step process to properly install canned foam around a window:

1. Prepare the Area and Shake the Can

Before applying the foam, make sure the area is clean and dry. Shake the can thoroughly to mix the contents, ensuring the foam dispenses evenly.

2. Apply the Foam from the Bottom to the Exterior

Start applying the foam at the bottom of the window gap, working your way up. The key here is to ensure that the foam reaches all the way from the exterior side of the framing to the interior side. You should be able to hear the foam hitting the exterior sheathing, which confirms that it’s filling the entire void.

If you can’t get the foam gun nozzle all the way to the back of the gap, pull the trigger slightly faster while moving the gun more slowly. This technique helps the foam expand fully and fill the entire space, preventing any hidden air pockets.

3. Apply a Second Layer for Full Coverage

While the foam will typically expand about an inch, it’s best to apply it in two layers. Once the first layer has expanded and begun to set, come back and add a second layer to ensure the gap is fully filled.

4. Cut Off Excess Foam Once It’s Dry

Once the foam has dried completely, use a flat razor knife to trim any excess so that it sits flush with the extension jamb. This step is crucial because if the foam sticks out too far, the drywall won’t sit properly against the framing. Keeping everything flush ensures a clean, professional finish when the drywall is installed.

Sealing Additional Gaps to Prevent Air Infiltration

While sealing around the window frame is essential, there are other areas in new construction where air can infiltrate. A comprehensive air-sealing strategy should also address gaps where framing members meet and areas where exterior sheathing is joined.

Caulking Between Framing Members

A crucial step in our air-sealing process is applying caulk wherever two pieces of wood meet. This includes areas where framing members butt together, such as corners, headers, and plates. We apply a thin bead of caulk along these seams and then smooth it with a finger to ensure a flush seal.

Why is this important? Even though exterior sheathing and house wrap (such as Tyvek) provide a level of protection, small gaps in the framing can still allow air to penetrate. Over time, these small leaks add up, reducing the home’s energy efficiency. Sealing these gaps with caulk ensures that no air can move through these seams.

Addressing Larger Gaps with Spray Foam

In some cases, gaps may be too large for caulk to be effective. For example, at the top of a window header, if the gap is ¼ inch to ⅜ inch wide, caulk might not be sufficient. Instead, the Great Stuff Big Gap Filler foam can be used to fill the void. This type of foam expands enough to bridge the entire width of a typical wall cavity, ensuring a complete seal.

For even larger gaps—those wider than three inches—open-cell spray foam can be used. This provides a flexible yet airtight seal that will prevent air movement while also offering some insulation benefits.

Why Proper Air Sealing Matters

Properly sealing the gaps around windows and throughout a home’s framing does more than just prevent drafts. It has a direct impact on energy efficiency, comfort, and even the longevity of the home.

     • Lower Energy Bills: By stopping air leaks, homeowners can reduce their heating and cooling costs significantly.

     • Improved Comfort: No more cold drafts in the winter or hot air infiltration in the summer.

     • Better Indoor Air Quality: Sealing gaps prevents dust, pollen, and outdoor pollutants from entering the home.

     • Enhanced Durability: Preventing moisture infiltration reduces the risk of mold growth and wood rot.

Final Thoughts

If you’re building a new home or replacing windows, taking the time to properly seal around them is one of the best investments you can make. Using the right materials—like low-expansion window and door foam—ensures that your home remains airtight, energy-efficient, and comfortable for years to come.

At Indiana Spray Foam, we prioritize air sealing as a crucial step in every project we take on. By combining proper foam application, strategic caulking, and comprehensive insulation techniques, we help homeowners achieve the highest level of energy efficiency possible.

For more information on how professional air sealing can benefit your home, contact Indiana Spray Foam today!