How to Install a Storm Window

Installing a storm window is a simple and effective way to improve your home’s energy efficiency and protect your primary windows from the elements. In this guide, we’ll walk you through installing a storm window, from measuring and ordering to the final installation steps. This Old House general contractor Tom Silva demonstrates the proper techniques for installing a storm window in the video above.

Measuring for Your Storm Window

Knowing the size of your window is important for purchasing the correct storm window. Here’s how to measure accurately:

Measuring the Width

Silva follows these steps to take three width measurements: 

1. Measure the width of the window opening in three places: top, middle, and bottom.
2. Use the smallest measurement when ordering your storm window.
3. Check if the window sides are parallel by comparing these measurements.

Silva explains that by using the smallest measurement, he makes sure the window isn’t too big and won’t overlap the frame. You can fill in gaps later with caulk.

Measuring the Height

The next step is to measure the height:

1. Measure from the outside of the window.
2. Place the tape measure where the side casing meets the top joint.
3. Extend the tape measure down to the sill for an accurate height measurement.

Considering the Window Type

The homeowner in the video needs an eastern-style storm window. Check whether your home needs this type by seeing whether your window has a flange that sits on the casing. This detail is crucial for proper fit and installation.

Preparing for Storm Window Installation

Prepare the window area before you begin installation:

1. Use a drill/driver to remove all screws securing the old storm window.
2. Carefully remove the old window, ensuring it doesn’t fall. Set it aside for proper disposal or recycling.
3. Use a paint scraper to remove loose paint from the window frame and trim. Focus on scraping the edges where the new storm window will be installed.
4. Locate the small grooves at the bottom of the window frame. If your windowsill has a raised edge, drill corresponding weep holes to allow water to escape. These holes prevent water from pooling and causing rot.

The homeowner in the video plans to paint her entire house soon, so Silva focuses only on painting the areas where the storm window will make contact.

Installing the Storm Window

Now that you’ve prepared the area, you’re ready to install the new storm window:

Applying Caulk

Caulk helps secure the window into the frame and prevent air and water leakage. Silva uses butyl caulk because it remains soft, pliable, and paintable over time. Butyl is a good choice if your window manufacturer doesn’t recommend a specific type of caulk.

Use a caulk gun to apply a bead of caulk around the perimeter of the window frame. Apply it only to the top and sides, leaving the bottom uncaulked for drainage.

Positioning the Window

Carefully lift the storm window into place, making sure it’s centered and level within the frame. Slide the window sash down to check that you have the correct positioning.

Securing the Window

Follow these steps to secure the storm window:

1. Screw the top of the storm window to the window frame.
2. Close the bottom sash, then secure the sides of the storm window to the frame.
3. Use a drill/driver to insert screws at regular intervals along the sides.

Adjusting the Expander

The last thing Silva does is add an expander to make up for any irregularities in the window frame:

1. Locate the metal piece at the bottom of the storm window, known as the expander.
2. Slide the expander down to make contact with the windowsill.
3. Use a hammer and putty knife to gently tap the expander tight against the sill to form a seal.

Finishing Touches for Storm Windows

There are a few final steps you can take to make sure your storm window functions properly:

• Check for proper drainage: Verify that the weep holes at the bottom of the window are clear and that any holes you drilled in the windowsill align with the window’s drainage system. Test the drainage by pouring a small amount of water and observing its flow.
• Inspect the seal: Check the caulk bead around the top and sides of the window for any gaps. Add additional caulk if necessary for a complete seal. Wipe away excess caulk for a clean appearance.
• Test the window: Open and close the storm window and look for smooth operation. Check that the window locks securely in both open and closed positions and verify that the expander at the bottom creates a tight seal against the windowsill.