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How to Install a New Window

Last modified: 2022-07-19 | Approximate reading time 5 mins

Cynthia Pigeon

Whether to revitalize your home or prevent heat loss, it may be tempting to replace your windows.

To achieve the expected results, adhere to the outlined procedure. Here are the steps to follow when installing a window. 

Step-by-Step Window Installation 


The first step consists of removing the mouldings and insulation within the frames. Then, measure the height, depth, and width. For the depth, determine the space between the exterior window frame and the drywall. Next, measure the frame casing from the outside. When doing so, measure in three different spots and note the shortest measurement. This way, the window will fit the opening.

How to Remove a Window Before Installing a New One

flowers in front of a window_how to install a new window

Proceed carefully since removing a mounted window can damage the surrounding structure should you go about it too fast. Also, remove and inspect the window frame to ensure the space is still in good condition. Should there be any moisture problems, you will need to rectify the issue first before continuing with the installation.

Remove frame and debris

Now, the time has come to remove the frame and check that the inside of the wall is undamaged. To avoid damaging anything, look for screws, nails, or debris, and clear everything out. Then, the next step will be to cut through the vertical window jambs with a reciprocating saw. Once you have done this, you can remove the window frame.

Should you struggle with this step, use a nail bar. If there is any sealant residue on the frame, remove it too. If needed, before proceeding, consult a professional for the best technique to employ. Finally, clean the window frame to ensure no small wood particles are left.

Window positioning and fitting

flowers in front of a window_how to install a new window

Now comes the time to mount your window on the heated side of the wall. To minimize heat loss, position the window back a quarter-inch inward. Then, make sure to leave a half-inch gap around the perimeter between the opening and the window frame, which will leave sufficient space to insulate.

Before fixing the window in the frame, ensure that it is not too tight of a squeeze and that the corners form a 90-degree angle.

To ensure the window is level, fit wedges every 16 inches under the window. Now, when it comes to the sides, insert at least three wedges: one on top, one at the bottom, and one in the middle. Should it be required, keep in mind there should be a wedge every 24 inches. Use rust-resistant wood screws to fix the windows to the frame. Lastly, note that the wedges will work as a benchmark when screwing. 

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Window Insulation

pot in front of window_how to install a new window

To insulate a window, choose between mineral wool, urethane foam, or polyurethane foam. Before selecting a product, know that urethane foam does not adhere well to PVC windows. However, it is more effective for basement windows, as mineral wool absorbs the moisture from concrete.

Ideally, choose a low-expansion polyurethane foam that is likely to expand sufficiently to ensure that no cavities are left unfilled. However, aluminum or vinyl windows risk not being adequately protected by this insulation. Both materials are prone to expand, which can cause the insulation to peel away from the edge of the window, leaving it unprotected against air infiltration. 

Window Caulking

Remember to seal your windows! To ensure a quality result, cut the end of the tube diagonally. Then place the tip of the nozzle against the frame and move at a steady pace to ensure an even amount of sealant is released. Make sure to maintain a constant rate: not too fast or too slow. If you go too fast, not enough caulk will be deposited in certain spots, and should you run it too slow, you risk over-applying caulk.

Finishing touches

The final step consists of installing the interior framing. Then, all you have to do is sweep up!

Tidbit of Advice for New Window Installation

Although you can retain the old window frame, you should still remove it when installing a new window. Keeping it in place can lead to air infiltration, which will in turn affect the overall energy efficiency of your new window.

Handy Tools and Project Materials 

Make sure to have on hand the following tools and materials:

  • Ruler;
  • New window;
  • Insulating material (urethane or polyurethane foam, or mineral wool);
  • Reciprocating saw;
  • At least three wedges;
  • Rust-resistant wood screws.

Steps to follow when installing a new window

1) Measurements

  • Measure the height, depth, and width in at least three spots.

2) Removing the existing window

  • Proceed cautiously and rectify any existing issues, if necessary.

3) Remove the window frame

  • Ensure that the inside of the frame is in good condition;
  • Remove all debris (screws, nails, or anything else that might hinder the process);
  • Cut through the vertical window jambs with a reciprocating saw;
  • Remove the remnants of caulking, if needed;
  • Wipe down the frame.

4) Positioning and fitting the window

  • Position the window from the inside and offset ¼ inch inwards;
  • Leave half an inch between the window opening and the frame;
  • Make sure the fit is not too tight and that the corners make a perfect 90-degree angle;
  • Fit wedges every 16 inches (at least at the top, bottom, and middle sections) under the window to maintain its level;
  • Screw in the window with rust-resistant wood screws.

5) Insulate the window

  • Insulate the window with mineral wool, polyurethane or urethane foam (ideally polyurethane foam).

6) Window caulking

  • Cut the caulking tube tip at an angle;
  • Apply sealant along the edge at a constant rate.

7) Finishing touches

  • Install inner frames.

Looking for more information regarding windows and doors? Check out our Door and Window Renovation Guide.  

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