DIY Replacement Windows

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. Better yet, you can do it in less than an hour.


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sunroom window
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Finding a Square

    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.

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Accurate Measuring

    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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Tools and Materials

    -- Utility knife

    -- Pry bar

    -- Pliers

    -- Hammer

    -- Level

    -- Sash replacement window

    -- Nails

    -- Caulking gun

    -- Caulk

    -- Wood putty

    -- Paintbrush

    -- Paint

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Score the Trim Seams

    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.

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Remove Inside Stops

    Slide a flat pry bar behind the inside stops and remove the pieces.

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Remove the Head Stop

    After scoring the head stop, gently pull it loose with pliers. Set aside for later use.

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Pry Loose the Old Jamb Liner

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

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Fold Back the Jamb Liner

    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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Remove the Old Window

    Remove the old sashes and jamb liner as a single unit. Ask a helper for assistance with larger windows. Use proper lifting techniques to avoid back injuries.

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Install Liner Brackets

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

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Attach Jamb Liner to Brackets

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

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Insert 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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Reinstall the Head Stop

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

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Attach the Inside Stops

    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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Reusing Trim

    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.

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