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Window Installation: How to Install Replacement Windows

New, vinyl replacement windows are low-maintenance, offer energy-efficient features and operate smoothly for years.

Replacement Window Options

Replacement Window.

You have two choices with replacement windows: full-frame windows and insert windows.

Full-Frame Replacement Windows

  • Replace the entire existing windows down to the house frame
  • Necessary when existing window frames are old and deteriorating
  • More advanced project


Insert or Pocket Replacement Windows

  • Replace only the existing sashes with smaller windows that fit inside the existing frames
  • Existing frames must be in good condition
  • More DIY-friendly than full-frame replacements


This project gives you step-by-step instructions for installing an insert or pocket window from the exterior of a house. Some replacement windows can be installed from the interior or exterior. Check the manufacturer's documentation to get specific instructions for your windows.

Good to Know

See Types of Windows: Replacement Window Buying Guide to learn about the different styles of replacement windows that are available.

Measure for the New Window

Measure the Height and Width of the Frame in Several Locations.

Determine height and width of the pocket opening. Measure inside the existing frame rather than between the stops that hold the sashes in place (you'll have to open the lower sash to get the measurement). Measure the height at the left, middle and right of the window. Measure the width at the top, middle and bottom. Use the smallest height and width measurements when ordering your windows. Watch How Do I Use a Tape Measure? for tips on taking accurate measurements.

Don't proceed until you have your new windows and have measured them all make sure they'll fit.

Good to Know

Lowe's will calculate the exact replacement window size for your application. Typically, the new window must be 1/2 to 3/4 inches smaller than the opening.

Remove the Old Window

Windows are built differently, so the steps needed to remove yours may vary. Sometimes it best to remove the sashes from the inside, but for the existing windows on this project, it will be easier to work from the outside.


Homes built before 1978 may have lead paint. Contact a professional for help.

Step 1

If you have a storm window, remove it first. Some storm windows can be removed by lifting them out of their channels. Others might require removing screws that hold the storm window in place.

Step 2

Score the Paint along the Storm Window Frame.

Score along the edge of the storm window frame with a utility knife, remove the screws and use a pry bar or putty knife to remove the frame. A paint multi-tool (sometimes called a 5-in-1 tool) is also helpful for this step.

Step 3

Remove any Existing Sash Springs.

If your existing windows are older, they may have either sash weights or sash springs that you need to remove.

  • If your window has weights, cut the cords and let the weight fall inside the frame.
  • If your window has sash springs, carefully remove them (image to the right). Raise the sash near the top of the window. The springs might have plastic covers; if possible, cut and remove them. If you can't remove them, they will break off when the springs are detached. Remove the screws holding the springs in place.

Sash springs are under tension and might snap into the window sash track. Be careful of the springs and plastic covers.

Step 4

Diagram Showing Exterior Stops, Parting Stops and Interior Stops.

Identify any stops on the existing window. An old, wooden window has stops holding the sashes in place: interior stops, parting stops between the two sashes, and exterior stops. If you're installing from the inside, remove the interior stops and leave the exterior stops in place. If you're installing from the outside, as with this project, remove the exterior stops but leave the interior stops in place.

Step 5

If Installing a Window From the Outside, Remove the Existing Exterior Stops and the Upper Sash.

Use a utility knife to score where the stops meet the frame. You might be able to pry them off. If you can't pry the stops off cleanly, they're probably embedded within the frame and need to be cut using an oscillating saw. Let the saw blade do the work and be aware of nail locations. Remove the top sash.

Step 6

After Removing the Upper Sash, Remove the Parting Stop and the Lower Sash.

Remove the parting stop and the lower sash.

Step 7

Fill all holes with wood filler and make sure you have solid wood where you'll screw the new window into the frame. If you find damaged or rotten wood, remove it and cut wood to replace it. Attach new pieces with screws and wood glue.

Good to Know

If your window has weight chambers, fill them insulation before installing the new window.

Install the New Window

Step 1

Clean the opening. Use a shop vacuum if needed to remove all the dust and debris.

Step 2

Apply Flashing Tape to the Window Sill.

Apply flashing tape to the sill. It should fit the length of the sill and extend up the vertical leg of the stool (the bottom ledge of the interior side of the window). Be sure to work it into the corner of the stool.

Step 3

If Necessary, Secure Shims to the Sill to Ensure it is Level.

Check the sill for level and to make sure there's no bowing. If necessary, use shims to make the sill level (illustration to the right). Make sure they are placed correctly for proper leveling and secure them with screws and flashing tape to prevent any movement.

Step 4

There Should be a Small Gap Around the Window Frame When You Temporarily Place the New Window.

Dry fit the new window into the opening. You should have a small gap around the frame. Set the window aside.


A large window can be heavy. Get help moving it and supporting it during installation.

Step 5

Caulk Around the Window Opening at the Stops, the Head and the Sill.

Apply a 3/8-inch bead of silicone caulk at the interior head (the top of the frame), the stops and the sill. See How to Caulk to learn to lay a bead of caulk.

Step 6

Insert Shims Around the Frame at Screw Hole Locations

Place the window in the opening, resting it against the interior stops and pressing it firmly against the caulk. Use shims to secure the window, placing them at the pre-drilled frame screw holes.

Step 7

Install Screws At the Pre-Drilled Holes and Through the Shims.

From the inside, drive screws into the holes and through the shims.

Step 8

Make Sure the Lower Sash Sits Correctly in the Window Frame.

Check that the sashes sit evenly in the frame. If needed, use additional shims at the meeting rails (the horizontal frame elements on the sashes that meet when the window is closed) to adjust the frame of the new window.

Step 9

Once the Window Operates Corectly and is Plumb, Level and Square, Cut The Shims.

Check for plumb, level and square and ensure the window operates properly. You can make any additional adjustments with shims. When everything is right, cut the shims.

Good to Know

To check for square, measure the diagonals of the new window frame, not the interior trim.

Step 10

From the outside, apply spray foam insulation recommended for windows into the gaps around the window. Don't overfill the gaps. Refer to the manufacturer instructions and see Do-It-Yourself Foam Insulation for tips. You can fill larger gaps with backer rod weatherstripping. Avoid batt insulation, which can absorb water.

Step 11

Measure the Height from the Sill to the Window to Size the Sill Adapter.

Measure the height from the bottom of the window to the sill to size the sill adapter.

Step 12

Cut the Sill Adapter to Size.

Use a sharp utility knife to cut the sill adapter to the appropriate width.

Step 13

Drill two weep holes at the bottom of the adapter and lock it onto the window.

Good to Know

Use a piece of scrap wood to protect the sill adapter when you tap it in place with a hammer.

Step 14

Apply Latex Caulk Around the Edges of the Window Frame.

Install exterior trim around the window frame with finish nails. Use a nail set to finish driving the nails to prevent denting the trim. Seal the edges of the trim with latex caulk. Don't cover the weep holes. Fill any noticeable nail holes with wood putty and paint the trim as needed.

Step 15

Apply Latex Caulk Along the Interior Trim.

Apply latex caulk along the interior trim to complete the installation.