How to Fit a Letterbox in a UPVC Door

In this blog article, we will guide you through the step-by-step process of fitting a letterbox in a UPVC door. Let’s get started!

Assessing the Door and Choosing the Right Letterbox

To ensure the proper fit for your uPVC door, begin by assessing its internal and postal slot sizes, as well as the thickness of the door.

The internal slot size refers to the dimensions of the opening on the inside of the door where your mail will be delivered. Measure the height and width of this slot to ensure that it’s compatible with the letterbox you plan to install.

Similarly, the postal slot size refers to the dimensions of the opening on the outside of the door where your mail will be collected. Take accurate measurements of this slot as well to ensure a proper fit.

In addition to the slot sizes, it’s crucial to consider the thickness of your uPVC door. Measure the thickness accurately, as this information will help you select the appropriate letterbox with the right telescopic sleeve. The telescopic sleeve ensures that the letterbox fits securely and snugly onto your door, providing a seamless appearance.

Gathering the Necessary Tools and Materials

Now that you have assessed your uPVC door and determined the correct measurements, it’s time to gather the necessary tools and materials for fitting the letterbox.

To ensure a successful installation, you’ll need a few essential items. First, grab a screwdriver, preferably a Phillips-head, as it will make the process easier.

Next, get your measuring tape ready to double-check the dimensions of your door and confirm the correct size for the replacement uPVC letterbox. It’s crucial to select a letterbox with telescopic sleeves that match the thickness of your door. This will ensure a proper fit and prevent any issues down the line.

Additionally, you’ll need a new letterbox that comes with weathersealing and non-rattle properties, ensuring its durability and protection against the elements. Don’t forget to have some silicone sealant on hand to seal any gaps and provide extra weatherproofing.

Lastly, grab a pencil to mark the areas where you’ll be making the necessary cuts and screw holes. If you’re feeling unsure about the process, consider watching video guides that provide visual assistance.

With these tools and materials ready, you’re all set to move on to the next step of fitting the letterbox onto your uPVC door.

Removing the Old Letterbox

To remove the old letterbox, start by unscrewing the screws located underneath it. These screws secure the letterbox to the door and need to be removed in order to take it off. You may need a screwdriver to do this. Once the screws are undone, you can move on to the next step.

The seals around the back of the old letterbox may need to be removed. These seals help to prevent drafts and keep your door insulated. Carefully peel them away from the door, being mindful not to damage them.

With the screws and seals removed, you can now pull the old letterbox away from the door. As you do this, you may notice that the other side of the letterbox will drop off. This is normal and expected.

Once you have removed the old letterbox, you can discard it. Make sure to dispose of it properly, following any waste disposal regulations in your area.

With the old letterbox gone, the hole for the new letterbox is now exposed. You can proceed to the next step of fitting the new letterbox into your UPVC door.

Preparing the Door for Installation

Before installing the new letterbox, you need to properly prepare the door for its installation. Start by removing the old letterbox. Unscrew the screws located underneath and carefully pull the letterbox away from the door. Once the old letterbox is removed, it’s time to prepare the new one. Begin by placing the gasket on the outside of the door. Make sure it’s positioned correctly. Then, mark and cut the hole for the new letterbox using appropriate tools. Take your time to ensure accuracy and precision.

Now, it’s time to install the new letterbox. Fit it with the gasket on the inside of the door. Use the same screws that you removed earlier to secure it in place. Make sure the letterbox is aligned properly and sits flush against the door. To ensure a secure fit, consider applying a small bead of silicone seal around the letterbox. This will help prevent water damage and improve durability.

Once the letterbox is securely fixed, check its functionality. Open and close it a few times to ensure smooth operation. Take a moment to clean any excess silicone seal or debris that may have accumulated during the installation process.

Installing the New Letterbox

After properly preparing the door, the next step is to install the new letterbox.

Begin by sliding the external plate of the letterbox through the hole on the outside of the door. Make sure it’s positioned centrally, with the flap facing down. Once in place, secure the plate with the provided screws, ensuring it’s tightly fastened to the door.

Next, take the internal plate and slide it through the hole on the inside of the door, aligning it with the external plate. Make sure the flap is also facing down. Use the screws provided to secure the internal plate to the door, ensuring a tight fit.

Now, insert the letterbox sleeve into the hole, connecting the external and internal plates. Apply pressure until the sleeve is firmly in place. This will provide additional support and stability to the letterbox.

Finally, insert the letterbox flap into the sleeve, ensuring it’s aligned properly. Test the flap to ensure it opens and closes smoothly.

Congratulations! You have successfully installed the new letterbox in your UPVC door. Now you can enjoy the convenience of receiving mail directly through your door.


In conclusion, fitting a letterbox in a uPVC door is a simple process that can be completed with the right tools and materials.

By assessing the door, choosing the correct letterbox, and following the step-by-step instructions, you can successfully install a new letterbox.

Remember to secure the letterbox properly and test its functionality to ensure it’s working properly.

With a little effort, you can have a functional and aesthetically pleasing letterbox for your uPVC door.




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Astframe is a uPVC Windows & Doors manufactured based in Norwich.

We supply a range of premium quality products including uPVC Windows, Doors, and Conservatories. Aluminium Bi-Folding Doors, Patio Doors.

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