How to Install a Retrofit Window

retrofit window

Upgrading your home with retrofit windows is a smart investment that not only enhances the aesthetic appeal of your property but also improves its energy efficiency. Retrofit windows, designed to fit into the existing window frame, offer a cost-effective and less intrusive solution compared to full-frame replacements. In this comprehensive guide, we’ll walk you through the steps of installing a retrofit window, ensuring you have all the information needed to make your home improvement project a success.

Understanding Retrofit Windows

Before diving into the installation process, it’s essential to understand what retrofit windows are and their benefits. Unlike new construction windows, which require the removal of the existing frame and trim, retrofit windows are installed within the existing frame. This method is less labor-intensive and can be completed without damaging the surrounding wall and interior finishes.

Benefits of Retrofit Windows

  • Energy Efficiency: Modern retrofit windows come with improved insulation features, such as double or triple glazing and low-E coatings, which significantly reduce heat transfer and lower energy bills.
  • Cost-Effective: Since retrofit installations are less invasive, they tend to be more affordable than full-frame replacements, making them an attractive option for homeowners on a budget.
  • Aesthetic Appeal: With a wide range of styles and finishes available, retrofit windows can enhance the look of your home both inside and out.
  • Increased Property Value: Upgrading to high-quality retrofit windows can boost your home‘s market value, making it a wise investment for the future.

Preparing for Installation

  1. Measure Accurately: Begin by measuring the existing window openings to ensure your new retrofit windows will fit perfectly. Measure the width and height in multiple places and use the smallest measurements to ensure a good fit.
  2. Choose the Right Windows: Select windows that match your home’s architectural style and meet your energy efficiency requirements. Consider factors like frame material, glass options, and manufacturer warranties.
  3. Gather Necessary Tools and Materials: Ensure you have all the tools needed for the installation, including a tape measure, level, caulking gun, shims, screwdriver, and sealant.

Step-by-Step Installation Process

  1. Remove Old Window Panes and Stops: Carefully remove the old window sashes and any stops without damaging the frame. Clean the area thoroughly to remove any debris or old sealant.
  2. Dry Fit the New Window: Before applying any sealant, place the retrofit window into the opening to ensure it fits properly. Make any necessary adjustments to align it perfectly.
  3. Apply Sealant: Apply a continuous bead of high-quality sealant around the perimeter of the window frame where the new window will sit. This will ensure a watertight seal.
  4. Install the Window: Carefully place the new retrofit window into the opening, pressing it firmly against the sealant. Use shims to secure the window in place and check for level and plumb.
  5. Secure the Window: Once the window is properly aligned, secure it by screwing through the frame’s pre-drilled holes into the existing window frame. Be careful not to overtighten and warp the frame.
  6. Apply Final Sealant: Apply sealant around the outside of the window to seal any gaps, ensuring a watertight and airtight installation.
  7. Finishing Touches: Install any interior or exterior trim pieces that came with your window or that you wish to add for aesthetic purposes.

Post-Installation Tips

  • Inspect the Installation: Once the window is installed, inspect it from both the inside and outside to ensure there are no gaps or misalignments.
  • Test the Window: Open and close the window several times to ensure smooth operation. Check the locks and other hardware to ensure they function correctly.
  • Maintenance: Regularly clean your windows and inspect them for any signs of wear or damage to maintain their performance and appearance.


Installing a retrofit window can significantly enhance your home’s energy efficiency, aesthetic appeal, and overall value. By following this step-by-step guide, homeowners can confidently undertake this project, ensuring a successful installation. Remember, accuracy in measurement, choosing the right window, and meticulous installation are key to enjoying the full benefits of your new retrofit windows.

Upgrading your home with retrofit windows not only contributes to a more comfortable living environment but also supports sustainable living by reducing energy consumption. Whether you’re an experienced DIY enthusiast or a first-timer, this guide provides the essential knowledge to tackle retrofit window installation with confidence.