How To Install a Window Sash Replacement Kit

Old, drafty windows can be an eyesore and can contribute to higher energy bills due to their inefficiency. While a full window replacement is sometimes necessary, installing a window sash replacement kit is a cheaper alternative for many homeowners, especially if the windows and frames themselves are in good shape. This method allows you to keep the existing window frame and maintain your home’s original look while upgrading the window’s moving parts. This Old House general contractor, Tom Silva, demonstrates the process of installing a window sash replacement kit with three apprentices from the Generation NEXT program. You can check out our walkthrough for sash window repair for more general repairs.

What Is a Window Sash Replacement Kit?

Window sash replacement kits are designed to replace the movable parts of a double-hung window without removing the entire window frame. They fit into existing window frames, which makes them ideal for a simple replacement or renovation. A window sash replacement kit consists of the following:

• Installation hardware
• Two jamb liners
• Two new window sashes
• Weatherstripping

Options for Replacing a Window Sash

If your house has double-hung windows equipped with sashes that are in desperate need of replacing, you have three options: install a window sash replacement kit, install a frame and sash unit (also called a “boxed” unit), or replace the entire window with a new one (this is the most costly and invasive). If the other parts of the window are in good condition, a window sash replacement kit is a good option since it is the least expensive.

Steps for Installing a Window Sash Replacement Kit

Step 1: Prep for Installation

Follow the steps below to prepare your window and the new kit for installation:

Measure the Existing Frame

Make sure you measure your window accurately so that all the pieces fit correctly. Refer to the manufacturer’s instructions for specific ordering guidelines based on these measurements:

1. Measure the width from the inside edge of one side jamb to the other.
2. Measure the height from the sill (where the exterior of the bottom sash contacts the sill) to the head jamb.
3. Take multiple measurements to account for any variations.
4. To ensure that you order the correct window sash replacement kit, refer to the manufacturer’s instructions on how to order based on these measurements.

Remove the Old Sashes

1. Pry off or unscrew the window stops on both sides. The window stops may be caulked to the trim, so it is best to score the joint first with a utility knife or putty knife. When prying the stops off, use care not to break them so that they can be reused.
2. Remove the lower sash and disconnect any cords or chains. Cut the cord or chain and let the weight fall into the pocket behind the trim.
3. Remove the parting bead, the small piece that separates the upper and lower sashes. It sits in a recessed groove (called a dado) in the sides and head jambs. The parting bead will likely need to be removed in pieces. That’s okay, as they can be discarded.
4. Take out the upper sash and disconnect its cords or chains. Cut the cord or chain and let the weight fall into the pocket behind the trim.
5. Remove the pulleys, which are typically screwed into the side jambs with slotted screws. If the screws are heavily painted over, align the slotted screwdriver over the screw and tap lightly to chip away the paint. Discard the pulleys.

Tip: Consider removing the weights and filling the weight cavity with insulation, such as low-expanding spray foam. Depending on the age and condition of your windows, this may be easier to do by removing the window trim, which sits directly over this cavity.

Inspect the Existing Frame

Before installing the new components, look for any of the issues listed below. Be sure to address them before installing your new sash kit to avoid repairs or having to redo the installation completely:

• Check for any rot or damage in the frame and repair as needed.
• Check that the sill and head jambs are level.
• Make sure the side jambs are plumb.

Step 2: Install the Jamb Liners

The jamb liners provide a smooth track for the new sashes to slide in, so pay close attention and install the pieces correctly so that the liner is stable. 

Position the Liner Clips

1. Align the clips with the exterior window trim, then pull back slightly (about 1/8 inch).
2. Place clips according to the manufacturer’s instructions, typically 4 inches from the top and bottom, with additional clips spaced evenly between. Make sure the clips are level so that the liners attach securely. In this video, Tom Silva installs five clips on each side.
3. Pre-drill starter holes for each clip.
4. Secure the clips with 1 to 1 1/4-inch galvanized roofing nails. Don’t drive the nails in very tight; just bottom them out so that the brackets can be tapped forward or backward if necessary. 

Attach the Jamb Liners

Once the clips are in place:

1. Make sure the weatherstripping on the liner overlaps the exterior trim.
2. Snap the jamb liner into the clips on each side of the window.
3. Verify that the liner fully engages with each clip along its length. If you’ve made sure that the pieces were properly aligned thus far, the liner should fit right into place.

Step 3: Install the New Sashes

With the jamb liners in place, you’re ready to install the new sashes. Complete this part of the process carefully so the sashes are properly seated in the balancing system. Any misalignment can cause binding or improper seating, leading to problems operating your sash, and even damage if the alignment isn’t corrected. 

Install the Upper Sash

1. Tilt the sash into the opening, engaging the lower pin into the metal cam in the liner.
2. Slowly lower the other side until its pin meets the opposite cam.
3. Gently lift the sash, depressing the jamb liner on both sides as you go.
4. Once the sash snaps into place, push it up to the top of the frame.

Installing the Lower Sash

1. Engage both sides into their respective tracks.
2. Insert the sash into the lower opening, keeping it level.
3. Apply slight pressure to ensure it’s seated properly.
4. Slowly push the sash up, allowing it to catch in the balancing system.
5. Test the sash by moving it up and down to ensure smooth operation.

Step 4: Add the Finishing Touches

After fitting and securing both sashes, there are a few final steps to complete the project, which will keep your windows looking good and working well long after your installation.

Replace the Window Stops

1. Measure and cut the stops to fit if necessary.
2. Nail the side and head stops back into place, keeping them snug against the jamb liners.
3. If needed, apply a small bead of caulk along the edges for a weather-tight seal.

Test and Adjust

Before the job is complete, run the following tests:

1. Open and close both sashes several times to ensure smooth operation.
2. Check that the sashes lock properly when closed.
3. Verify that the weatherstripping makes good contact all around. This is important for maintaining and ensuring energy efficiency.
4. Make any necessary adjustments to the jamb liners or stops to improve the performance.

Tips for a Successful Installation

Here are a few additional tips and best practices for a successful and professional-looking window sash replacement:

• Double-check measurements: Inaccurate measurements lead to a poor fit. Always double-check your dimensions before ordering your sash replacement kit.
• Use high-quality materials: Invest in a good-quality sash replacement kit and tools for better performance.
• Work carefully and methodically: Don’t rush the installation—careful and methodical work results in a more professional outcome. Take your time throughout each phase of the project for the best results.
• Seek expert advice: If you’re unsure about any steps, consult experts or watch detailed video tutorials. Learning from professionals can significantly ease the process, and if you’re not confident in your abilities, they can take over for you. 
• Perform regular maintenance: Regular maintenance of your sash windows can extend their life span and keep them working well. Keep the tracks clean and periodically check the weatherstripping to make sure the seal is tight.