Project Guide

How to Install a Window

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Replacement Window Types
Man doing a dry fit of a remodel window.

In general, windows come in two basic types: new construction and remodel.


  • A new construction window will usually have a nailing flange to attach to a rough opening. 
  • A remodel window will be made to fit within the existing finished opening. 

A remodel window is faster and easier to install but it will have less glass to let light in. The window itself is smaller on a remodel window vs a new construction window. This is because it’s designed to fit inside a finished opening with an existing window frame instead of a rough opening.

If you have any questions, visit a Home Depot store and talk with an associate in the millworks department. They can answer your questions, help you find in stock items or place an order for custom windows.

Measure the Window Opening
Man measuring the width of a window.

To get a good fit for your replacement window, you’ll need to measure the pocket opening. Take your time to carefully note the exact height and width of your window. Correct measurements now will save you from sanding the frame and adding filler strips later.  

Here are some tips and terminology to know when measuring the window opening:

  • Stop Moulding - This is the part that holds the window in place inside the frame.
  • Frame Width - When you measure the width of the frame, be sure to go to the outside edge of the stop moulding.
  • Frame Height - Measure the frame height from where the lower sash contacts the sill to where the upper sash touches the header.

Measure for replacement windows by following these steps:

  • Start by measuring the height inside the existing frame in three places. Check the height in the middle of the window and on the left and right sides. 
  • Next, similarly measure your width. Get measurements for the top, middle and bottom.
  • Record your measurements. 
  • Use the smallest measurements for width and height to help choose your new window size. 

Your new window needs to be about 3/4 inches smaller than your window opening. This is to keep you from needing to reframe the opening. 

Remove the Existing Window
Man removing an old window with two blue taped Xs.

Before you continue with your window removal, ensure you have everything you need to complete the job. Check the new windows for damage, quantity and size.

When installing windows on the upper levels of your home, you may want to rent scaffolding. You’ll have more room to maneuver up there rather than on a ladder. Because windows are difficult to handle, find someone to help you when working above the first floor. Always wear eye protection and gloves when you replace window glass and fiberglass insulation. 

Be careful once you remove the interior stop moulding. If the window wasn’t previously fastened in place properly, it could fall out without warning.

  • You might have to cut through old paint or caulk with a utility knife to complete some steps.
  • Remove interior stop moulding carefully because you may be able to reuse it.
  • If you have thin, sharp metal channels around your window, use cut-resistant gloves to pry the metal loose from the frame. Then, pull it out when you remove the sashes. 
  • Remove the fasteners that are holding the old window to the frame.
  • Lift out the old window. It will likely come out in two parts.
  • Cut any balance lines or window weight connections.
  • Remove the old balance system.
  • Remove any fasteners that are sticking out.
  • Clean the window opening thoroughly. Remove all the old caulk.
  • Fill any holes in the surface and add insulation as needed. 
  • Inspect the blind stop (exterior stop moulding) to see if it needs to be replaced. If it’s damaged or decayed, replace it in the next step.

Tip: If you’re replacing a damaged window, be cautious and avoid jagged glass. Use painter's tape to cover any cracks to prevent shards from falling during the removal process. Cut-resistant gloves are a smart choice for working with glass.

Prep and Dry Fit Window
Man removing old trim from inside a window opening using a pry bar.

The window is out of the wall, so now you can check all remaining wood for structural damage. 

  • Replace any damaged areas.
  • Install new blind stop moulding, also known as exterior stop moulding, if needed.
  • Center the new window in the opening, supporting it with wood blocks and shims.
  • Make sure the window is plumb. Level and adjust the shims if needed.
Install the Remodel Window
Man applies caulk along a window frame.

Once you’ve prepared your new remodel window and the old window frame, it’s time to install a window into that opening:

  • Apply a bead of caulk to the inside face of the blind (exterior) stop moulding.
  • Place the window into the opening, pressing it tightly against the caulk.
  • Put shims where pre-drilled holes are to secure the window. 
  • Measure the window diagonals to check that the window is square. The measurements should be the same. 
  • If needed, adjust the fit with shims until the window is square. 
  • Drive screws into holes through the shims and into the frame.
  • Trim the shims by scoring with a razor knife and breaking off flush with the window frame.
  • Re-check that sashes are even and the window is level.
  • Fill the gaps between the window jambs and the framing members with loosely packed fiberglass insulation.
  • Install interior stop moulding with finishing nails.
Paint and Finish the Window
A man paints a window sill indoors.

Now that you’ve installed the window, the hard part is done.


  • When the caulk dries, paint to match the trim on the rest of your house.
  • Once your window trim is painted, your new remodel window will blend right in with the rest of the house.
Tips and Tricks for Choosing Replacement Windows
A person holding a wood shim next to a remodel window.

Windows will differ by material and design, so it's important to know what type of window you currently have and what type of window you are installing. 

Here are a few tips to keep in mind when choosing replacement windows:  

  • Homeowners often opt for vinyl and metal windows because they have a nailing flange that attaches to your home to keep water out. Because the flange must be attached to the rough opening of a wall, the process of how to install a vinyl window with nailing flanges is a bit different than the installation of a remodel window, shown in this guide.
  • If you’re planning on installing a new construction window in an existing home, there’s much more work involved. This includes cleaning out the window reveals, removing siding or brick moulding, adding more insulation and sealing it. 
  • Overall, most types of windows are installed the same way. Each manufacturer has specific instructions for their windows, but the basics are identical.
  • Keep the old windows in place until you have looked over the new ones for damage and checked their size to see that they fit.

Now that you understand the basics of window installation, you can replace damaged windows and update older style windows. Maybe you're ready to install new doors to match. On the inside of your home, it may be time for new curtains and window dressings. 

Consider a boom lift rental to reach your windows safely. Use once, then bring it back - no maintenance required and you won’t need to store it either. Or, if you don’t have the time or tools for this window DIY project, leave it to our experts. We offer window installation services to help you with your remodel or replacement windows.