Using common carpentry tools, you can install a sash kit or window insert from inside your home without destroying the surrounding interior molding or exterior casing.

If you have the right tools and tips, installing a window yourself can be a weekend project. Whether you're replacing a damaged window or just want a new look, we will show you how to get the results you want without calling in help from a professional. Check out our steps below and get started today.

Installing a window yourself will only work when the replacement window is the same size and shape as the old one and when the existing window opening is square. To determine whether your window opening is square, measure it diagonally one way (from the upper left corner to the lower right corner) and then the other (from the upper right corner to the lower left corner). If the opening is square, the two measurements will be the same, give or take 1/8 inch. The slightest deviation from square can prevent the sash from closing and the weather stripping from sealing properly. If that happens, you'll be stuck with drafts, condensation, and high utility bills.

  • Working time 5 hrs
  • Start to finish 5 hrs
  • Difficulty Kind of hard
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What you need

Tools
Materials
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How to do it

Step 1

Measure Window

Successful replacements depend on good measurements of the existing opening to find out how big your new window needs to be. Start by measuring between the left and right jambs at the top, middle, and bottom of the window; the shortest of these three measurements is the window width. After that, measure the distance between the head jamb and sill at the far left side, middle, and far right side of the window; the shortest of these three measurements is the window height.

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Step 2

Remove Trim and Head Stop

Score the paint where each piece of trim meets the existing window casing. Scoring the seams prevents the wood from splitting when you remove the trim pieces. Slide a flat pry bar behind the inside stops and remove the pieces.

Next, score head stop and gently pull it loose with pliers. Set aside for later use.

If you wish to remove the surrounding trim as well, use a utility knife to slice through any paint or caulk between the interior casing and the wall. Use a flat pry bar and a scrap piece of wood to remove the casing. If you will reuse the casing, use slip-joint pliers to remove the screws.

Tip: After removing a stop or other trim pieces, use pliers to pull the nails through the back of the piece. Doing so reduces the odds that the piece will split or fracture.

Step 3

Remove Jamb Liner

Raise the lower sash 6 to 8 inches, then pry back the old jamb liner. Repeat with the upper sash.

Fold the jamb liner at a 90-degree angle underneath the sash. Repeat with the upper sash, folding the jamb liner across the top of the sash.

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Step 4

Remove Window

Remove the old sashes and jamb liner as a single unit. You may need a helper for assistance with larger windows. With a helper standing outside to catch the window, start prying outward. You may need to tap the jambs with a hammer. Once the window is loose and ready to fall, go outside to help pull it out. Use proper lifting techniques to avoid back injuries. 

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Step 5

Insert New Jamb Liner

Install a liner bracket every 4 to 5 inches along each jamb. Make sure each bracket is level before you nail it on.

Attach the jamb liners to the liner brackets. Each liner should pop into place.

Step 6

Install Sashes

Insert the upper sash in the exterior track of the jamb liner. Open and close the sash to make sure it slides smoothly. Insert the lower sash in the interior track and check that it operates.

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Step 7

Install Head and Side Stops

Reattach the head stop. Set the nails below the wood surface. Fill the holes with wood putty and touch up with paint.

Reattach the inside stops. Set the nails and fill the holes with wood putty. Caulk the seams and touch up with paint.

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Step 8

Remove Casing

Use a utility knife to slice through any paint or caulk between the interior casing and the wall. Use a flat pry bar and a scrap piece of wood to remove the casing. If you will reuse the casing, use slip-joint pliers to remove the screws.

Step 9

Remove Sash Weights

If you have an older wood window with sash weights, pull back the cords or chains and cut the ones that attach to the weights for the lower sash. Pull down the upper sash and do the same. Remove the sash weights.

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Step 10

Remove Molding

On the exterior cut through any caulk and pry out the molding all around the window. If your window has a flange that is covered by siding.

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Step 11

Remove Stool and Apron

Inside the house pry out the stool (inside sill). It may be easiest to cut through the nails first (see next step). Also remove the apron, which is attached to the wall directly below the stool.

Step 12

Cut Through Nails

Cut through the nails that attach the jamb to the house's framing. A reciprocating saw works best for this, but you can also use a hacksaw. Or slip the notch of a flat pry bar onto the nail's shank and bang hard with a hammer to break the nail.

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Step 13

Remove Insulation and Sashes

Pull out any insulation and other obstructions, and check that all the nails have been removed. Remove one or both sashes.

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Step 14

Pull Out the Window

With a helper standing outside to catch the window, start prying outward. You may need to tap the jambs with a hammer. Once the window is loose and ready to fall, go outside to help pull it out.

Editor's Tip

How to Detach Windows from the Exterior

A metal or vinyl window may have a flange that is nailed to the sheathing and covered with siding; in that case you must cut back the siding. Molding that rests on top of siding is the easiest to remove. Siding butts up against brick molding.

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