As nice as it is to buy new windows, sometimes it just doesn’t make sense—especially if you’re just dealing with a broken pane of glass in a single frame. With the average double pane window running around $300 installed, it’s much more cost-effective to replace a broken pane instead of replacing windows—especially if you’re willing to do some of the work yourself. In fact, older single glazed windows are exceptionally easy to repair, since they’re usually joined a little less tightly than newer models.

Still, you shouldn’t attempt to fix a window without doing your homework first. You could potentially cut yourself or further damage the window if you go about it in the wrong way. Here’s what to know when replacing a glass pane in a window—before you begin.

older double hung window

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What Types of Windows Make Good Candidates for DIY Repairs?

Different types of windows require various levels of skill to repair. For instance, if you have insulated or double pane windows windows, your best bet is to take them to a glass repair shop. A window repair specialist will know how to properly measure the width and dimensions of the glass pane, and can connect you to the manufacturer if you need to reorder specialty products, like glass within energy efficient windows with Low-E glazing. The final cost for professional services varies, of course, mainly due to the type of windows you have. Typically, a professional replacement will cost you between $50 to $100 for a 12-square-inch panel.

Repairing yourself can save you quite a bit of money—a DIY job costs around $3.00 per square foot—but it’s not recommended unless you’re working on a single-glazed window with wooden sashes. Double-glazed windows—the kind favored by most modern homes—generally require professional know-how, since they’re designed to be airtight and may be filled with gas insulation, as well.

Clean Out the Old Glass and Putty First

Safety first! Since you’ll be handling broken glass shards and splinters, you need to protect yourself with goggles and very thick gloves. At this point, you might consider removing the sash from the window, especially if the glass pieces are stuck in the frame. Carefully, with gloved hands, wiggle the broken glass loose from the window putty. You can use a heat gun to soften the glazing compound around the glass if the pieces are very stubborn, then gently tap around the sides of the frame with a hammer.

Once you’ve pried all the pieces loose, dust around the edges of the frame with a wire brush to get rid of any remaining glass dust.

Next, prepare to clear out the old putty around the window. If you haven’t already, get out your heat gun to loosen the caulking, making it easier to remove. Then use a painter’s chisel to scrape the putty off of the frame.

Flip the chisel over and use the tip of it to pry loose the glazier’s points—the metal triangles underneath the putty that hold the glass in the frame. Now you’re ready to prepare the frame for the new glass and putty.

Then, Oil the Frames to Extend the Life of Your Caulking

Lightly sand the interiors of the frames to get rid of any last putty residue, then wipe them down with a cloth.

Add a thick layer of linseed oil to the frames, and give it some time to soak into the wood. Oiling the frames keeps the putty pliable and flexible, preventing it from drying out too fast. That means you won’t have to re-caulk your windows as frequently.

Apply a Fresh Layer of Putty to Prepare for the New Pane of Glass

Once you’ve given the linseed oil some time to saturate the wood in the frames, it’s time to lay down some new putty to keep the glass in place.

Knead the putty with your hands until it’s warm and flexible, then press a thin layer into the inside of the frame.

Repairing a window frame

Press the Glass into Place and Add New Glazier’s Points

Gently place the glass pane into the putty between the two frames. Make sure it’s the right size—it shouldn’t be more than an inch smaller than the area it’s meant to fit. Wiggle the pane into place, allowing some of the putty to squeeze out over the edges of the glass.

Use the chisel to place glazier’s points into the frame, against the glass. Put one point on each side of the frame, in the center. Place additional points every four to six inches.

Add Additional Putty Around the Glass and Frame to Create a Seal

Employing the same process you used before, use your hands to warm the putty and then place it in a thin strip around the edges where the glass meets the frame. Use a putty knife angled at 45 degrees to smooth the putty into the crease, and scrape the excess putty off the window.

Allow the putty to dry for a few days, then paint it with an oil-based primer and a layer of exterior paint. Do the same for the opposite side, and there you have it: a brand new window pane for a fraction of the price of a replacement!