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Published on November 10, 2023 10:09 PM
Replacing an existing casement window is a project that can revitalize a room and improve energy efficiency. While challenging, this task is rewarding for skilled DIYers with a solid understanding of home improvement basics. This guide will provide detailed steps for those ready to tackle this project.

Materials You’ll Need
1. Replacement casement window
2. Screws/nails
3. Hammer or nail gun
4. Power drill
5. Pry bar or chisel
6. Utility knife
7. Silicone gun and silicone
8. Shims
9. Insulation (non-expanding foam or fiberglass)
10. Waterproof flashing
11. Safety glasses and gloves
12. Screwdriver

Step 1: Preparation
First, understand the type and dimensions of the replacement window you’ll need. Measure the existing window accurately, and purchase a new casement window that fits these dimensions. Don’t forget to review local building codes and obtain any necessary permits.

Installing casement windows
Installing casement windows
Step 2: Removing the Old Window
a. Start by carefully removing the interior trim and casing with a pry bar or chisel, ensuring not to damage the surrounding wall.
b. Unscrew and remove the old window sashes from the hinges.
c. If your window is sealed with silicone or adhesive, use a utility knife to cut around the window unit for easier removal.
d. Check for fixings in the frame or potential fixing straps Gently take out the old window frame, making sure not to damage the house framing.

Step 3: Preparing the Opening
a. Clean the opening area, removing old silicone, debris, and any nails or screws.
b. Examine the cill and jamb for any signs of water damage or rot, repairing any compromised areas.
c. Ensure the window opening is level and square, as an uneven cill may require adjustments or shimming for a snug fit.

Step 4: Installing the New Window
a. Place the cill in first on a bed of clear silicone or mortar. Ensuring it’s perfectly level. Dry fit your new window to make sure it fits properly. Then, remove it and apply a bead of silicone along the inside edge of the exterior casing.

b. Carefully position your window in the opening, using shims to secure it in place. Check that the window is sitting plumb, level, and square within the opening.
c. Once correctly aligned, use screws or nails to secure the window through the jamb into the framing.

Step 5: Insulating and Sealing
a. Fill gaps between the window frame and opening with insulation, ensuring there’s no bowing or distortion.
b. Install waterproof flashing around the exterior of the window as required.
c. Seal the exterior of the window with silicone to prevent air and water leakage.

Step 6: Reinstalling the Trim and Finishing Up
a. Replace or install new interior trim around the window as needed.
b. Conduct a final inspection to ensure all screws are tight, and the window opens, closes, and locks smoothly.
c. Clean the new window and surrounding area.

Casement window replacement can enhance your home’s aesthetic, natural lighting, and energy efficiency. While this task demands precision and a fair level of DIY experience, it’s immensely satisfying once completed. Follow all safety precautions and don’t hesitate to seek professional advice if necessary.

Disclaimer This guide is intended for informational purposes and does not replace professional advice. Structural or significant changes to your home should always involve consultation with a professional to ensure safety and compliance with local building codes.

Installing casement windows
Colin Greenslade
Written by Colin Greenslade
I'm the founder of Colin's Sash Windows. I disrupted the sash windows market in the UK in 2014 by introducing fixed prices for uPVC sash windows in the UK. Before this they were generally only available at very high prices through window installers. Today our business is one of the market leaders in supply only windows, doors and roofs in the UK.

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