Adjusting a UPVC Window in 9 Easy Steps Illustrated

1. Examine the bottom of the sash to determine its compatibility with the frame. Operate your uPVC window multiple times. The lower part of the sash should effortlessly glide into the window frame. If it fails to do so and instead gets stuck against the frame or seal, the window requires an increase in its height.

On the flip side, if your uPVC window sash doesn't make direct contact with the frame when closed, but rather rests about 1/16 inch (0.16 cm) above it, you'll need to reduce the window's height.

It's worth noting that a window "sash" refers to the panel, usually composed of multiple glass panes, that can be raised and lowered to open the window.

2. Fully open the window. This will make it easier for you to access the small screws that need to be loosened in order to adjust the window's height.

Since the process of adjusting the window may take approximately 15-20 minutes, plan to do it on a day free from rain.

3. Loosen the 4 screws that hold the uPVC casement to the left side of the frame. Once the window is open, you'll notice 4 small screws securing a metal strip to the window frame. Loosen each of these screws by turning them counterclockwise approximately 1 full revolution.

The casement of a uPVC window refers to the metal strip that directly fastens to the wooden window frame. The hinges that allow the window to open and close are also attached to the casement.

When adjusting the window's height, ensure not to loosen the screws that hold the hinges to the frame.

4. Loosen the screws that hold the window casement to the right side of the frame. Now that you have loosened the screws on one side of the casement, proceed to loosen the screws on the right-hand side of the frame. Just like before, turn each screw counterclockwise by 1 full revolution to loosen them.

It's likely that all 8 screws holding the window sash to the casement will require a larger Phillips head screwdriver. If it doesn't fit, try different sizes of Phillips head screwdrivers until you find one that fits comfortably into the screw.

5. Adjust the height of the window by pressing or lifting the window sash. Once you have loosened the 8 screws, you will be able to raise or lower the height of the movable window panel. If the window hasn't been fully closing, move the window slightly downwards. If the window sticks against the frame when closing, move it slightly upwards.

You may need to provide support to the weight of the window panel until the screws have been tightened again. If the panel is particularly heavy, it may droop under its own weight.

6. Once the window sash has been adjusted, tighten the 8 screws. Give each of the 8 screws that you previously loosened a full clockwise turn to tighten them. Then, close the window multiple times to verify that it opens and closes correctly.

  • Ensure that your uPVC window fits snugly into the frame when closed, preventing any drafts from entering your home through misaligned windows.[6]


  • 1

    Open your uPVC window and locate the lock-adjustment head. If your uPVC window opens outward, you can adjust the lock on the sash by moving it forwards or backwards. Look for the lock-adjustment head on the lower half of the open window sash, positioned halfway between the lock and the bottom of the sash.[7]
    • By adjusting the lock position, you can ensure that the window seals properly. This is particularly useful if the locked window is loose and drafty or if the lock mechanism doesn't securely catch and seal the window.
    • This type of window is commonly referred to as a "long-bottom lock," and the part that allows you to adjust the lock's position is known as the "head."
  • 2

    Insert an Allen wrench into the lock head. Most uPVC window brands utilize an Allen wrench to adjust the lock's placement.[8]
    • If you don't already have an Allen wrench, you can purchase a set from a local hardware store.
  • 3

    Turn the wrench either clockwise or counterclockwise to move the lock forwards or backwards. Clockwise turns will move the lock backward (away from the lock mechanism), increasing the pressure exerted on the window when locked. This helps improve the seal and prevents drafts from entering.[9]
    • Alternatively, turning the wrench counterclockwise will loosen the pressure when the window is shut. This is useful if your window doesn't lock completely or requires excessive force to lock.
    Drew Hawkins1


    Add a New Question

    • Question

      I'm having trouble moving my UPVC sliding window. How can I adjust it?

      Try fully opening the window and loosening the four screws on each side of the frame. Then, adjust the panel's height by raising or lowering it. Once you're done, tighten all eight screws to securely hold the window in place and close it.
    • Question

      How can I fix a draughty uPVC window?

      You can attempt to improve the seal by adjusting the lock position. Open the window and locate the lock-adjustment head. Use an Allen wrench to turn the lock backwards, increasing the pressure it applies to the window when locked. This will create a tighter seal.


      What could be the reason behind the improper closure of my uPVC window?

      To resolve the issue, you might need to make adjustments to the window's height within the frame. Begin by fully opening the window and loosening the four screws on each side of the frame. Then, lower the window slightly and securely tighten all eight screws. Check if the window closes properly. Repeat the process as required for further adjustments.

      • Ask a Question


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      Updated: August 30, 2021

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      Categories: Doors and Windows

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