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How to Replace Casement Windows in 12 Easy Steps

handyman repair window

Casement windows have a design that uses a crank handle to open and close the windows instead of sliding them, which helps make them less drafty and more attractive. However, like anything that moves, it tends to break down from time to time, requiring repairs. If your window needs fixing, but you aren’t sure where to start, we’re here to help. Keep reading for a step-by-step guide to replacing your casement windows and getting them to work like new.

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Replacing a Casement Window

Getting Prepared

To replace a casement window, you will need to remove the molding around the window inside and out. You may also need to remove shingles or siding to gain access to the frame, which is a little beyond the scope of this article, so we recommend hiring a professional if you don’t have experience with shingles or siding. However, many repairs won’t require these extra steps.

man doing window repair
Image Credit: Pixel-Shot, Shutterstock

Get Your Tools Together

We recommend that you gather your tools before you begin your project, so you don’t need to make any unexpected stops to run for supplies. Once you get started, you will have a large hole in your home or garage until you finish, so it’s better to take the time to plan. Here is what you will need:

  • Tape measure
  • Hammer
  • Putty knife
  • Pry bar
  • Wood glue
  • Cat’s paw nail puller
  • Level
  • Wood wedges
  • Water seal gasket
  • 5-inch galvanized roofing nails
  • Finishing nails
  • Replacement window

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The 12 Steps to Replace Casement Windows

1. Measure the Window

The first thing that you will need to do when you decide to replace your casement window is to measure it to get the right-sized replacement. Measure the height and width of the glass part of the window several times until you get a matching number, so you know that you’ve measured correctly, and write down the numbers. Some casement windows will have a model number etched into them, which will make it easier to order replacements. Try to order the same brand if possible, and use the numbers you’ve written down if you can’t.

handyman installing window
Image Credit: Hryshchyshen Serhii, Shutterstock

2. Remove the Trim

Once your replacement window arrives and you inspect it to make sure it’s similar to the one currently installed, it’s time to remove the molding around the window on the inside of your home using a putty knife and a hammer. If you are careful and don’t try to work too quickly, you should be able to get the molding off without breaking it, and you should be able to reuse it. If you get a small crack, you might be able to repair it with wood glue, but you’ll need to replace it if there is too much damage. Once the molding starts to lift away from the wall, a small crowbar may be able to help you remove it more quickly.

3. Remove Extension Jams

Next, you will need to remove the extension jams that fill the space between the window frames and the molding. Like the molding, these boards might be somewhat delicate and are held in place by only a few finishing nails, so it shouldn’t be too difficult to remove them the same way as the molding.

window repair
Image Credit: Try_my_best, Shutterstock

4. Pull Out the Roofing Nails Holding the Window Flange

Next, we will need to move outside to remove the roofing nails through the flange holding the window in place. If you have siding or shingles covering the window flange, you must remove them to expose the nails. We recommend using a hammer, along with a cat’s paw, to grab the nails so they will come out easily, as there are typically quite a few around the flange. Leave the top center nail until last to prevent the window from falling out while you are working.

5. Remove the Window

The window should come out easily with all the roofing nails removed from the flange. However, we recommend getting a helper as some windows can be quite heavy. Set the window aside to keep working once it is free of the house.

man removing old window
Image Credit: Africa Studio, Shutterstock

6. Prepare the Frame

Next, check that the new widow fits correctly. Set that aside, and check your frame to make sure it’s level. There is a good chance that it is because it already had a window in it, but you can add wooden wedges to make it straight if it isn’t.

7. Apply a Water Seal Gasket

Now you will need to apply a water seal gasket on the outside of the house. It needs to run along the frame at the bottom and sides of the window. You will also place a piece on the bottom of the frame over the windowsill. This gasket will prevent moisture from entering your home, which can compromise your energy efficiency and cause deterioration of the frame.

basement window repair
Image Credit: Pavel L Photo and Video, Shutterstock

8. Install the New Window

Now it’s time to put the new window in place. Check it one more time to make sure it’s level, and make any adjustments before you begin to hammer the roofing nails into the flange of your new window. Start by hammering in the top center nail to keep the window stable while you complete your work. Then, install a roofing nail through the center of every other hole in the flange around your new window.

9. Place a Strip of Water Seal Gasket Over the Top of the Flange

After all the nails are in place, you will need to add a strip of water seal gasket over the top of the flange to help keep out moisture and to prevent rain from leaking behind the flange and entering the house.

man insulates the window
Image Credit: Aleksey Kurguzov, Shutterstock

10. Replace the Extension Jams

Inside the home, it’s time to replace the extension jams to fill in the area between the window frame and the molding. Hopefully, you were able to remove them without causing any damage, and you can quickly hammer them back in place. If some boards have too much damage to use again, you might need to purchase replacements at your local hardware store.

11. Replace The Molding

With the extension jambs in position, it’s time to replace the molding. Hopefully, you can use all of the same wood for this step. That said, we recommend replacing the finishing nails.

man repairing window
Image Credit: Elizaveta Galitckaia, Shutterstock

12. Paint

Even if you can get the molding and the extension jams off the frame without breaking them, the putty knife and prybar can scrape and remove paint, so you’ll likely need to repaint the frame when you finish installing the window to complete your project.

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While quite a few steps are involved, it’s not that difficult to change a casement window if you take your time and don’t try to rush through it. The molding and extension jams are especially troublesome because they can be difficult to replace and are easy to break. The water seal gasket helps prevent moisture from creeping behind the flange, which can cause premature failure in the window and other damage to your home.

Featured Image Credit: Andrew Angelov, Shutterstock


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