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How To Fit A Double Glazed Window

homeowners find difficulty in fitting their upvc windows by themselves. That Is why they want a complete guideline about tools, materials and methodology to fit their windows.  So that they can fit their window on their own without hiring a professional.

As I fitted a upvc window in my home recently after doing a thorough research. I recommend you to fit your window by yourself to save money and time. In this article, you’ll have the opportunity to explore everything about how to fit a double-glazed upvc window by yourself.

Tools required

You require following tools to fit a upvc window:

  • Gloves
  • Measuring Tape
  • Lead Pencil
  • Hammer
  • Masonry Chisel
  • Screwdriver
  • Spirit Level
  • Electric or cordless and drill
  • Spatula
  • Plastic bins

Material Required

You require following materials to fit a upvc window:

  • Cleaning fluid
  • Cement
  • Silicone or sealant
  • Chisel


Get all the tools and materials ready before you start fitting the window. Additionally, make sure every tool works properly. It will take some of your time and effort, so be prepared mentally. 

Things to remember:

You must keep the following points in mind when you are going to fit a window. 

Fenestration Self Assessment Scheme (FENSA) registration

Make sure, quality of your window meets the minimum standards and it also goes well according to the legal policy of your building or society.

Proper supply of upvc windows is essential 

Double glazed upvc windows can be damaged easily. however, you should buy it from a well reputed, FENSA registered company. Try to buy it from a company that specifically sells windows. You can buy it from Trade upvc doors and windows.

How to Fit Double-glazed UPVC Windows

Removing the old windows:

First of all, you have to remove your existing window.

Measure the space into which you’ll install your uPVC window

Measure the height and width of your existing window. Because, it will help you to choose the appropriate  height and width of the new window. Moreover, measure the height and width two to three times to get an appropriate measure.

Remove the screws holding the existing window 

Unscrew all the screws of the existing window frame using a screwdriver and head bit. Your window sas can break down during this process, but it is ok as you have to throw it in the bin anyways.

Cut the old window frame 

Remove the sealant using a knife and unscrew all the screws. Finally, place a pry bar between the wall and the frame. Now, exert pressure to remove the frame away from the wall.

Hammer the previous window frame out of the wall 

Now, pound the corner or horizontal/vertical edges with a mallet softly from inside of your place to loosen the frame. Once the frame is loosen, you can remove the frame easily.

Scrape away any sealant 

Lastly, scrap away all the sealant or debris in the space left using a knife. 

Prepare the frame space

Now, measure the area of space again to make sure that the new window frame fits in this space accurately.

Prepare the sill:

Purchase uPVC windows frames slightly smaller than the opening of the wall

Always buy a window 10 mm smaller than the space you left for installing the window. Because, you’ve to leave a gap of 5 mm between the wall and frame on both sides.

Use super glue to fit the sill end caps to the new frame

Usually 4 inch plastic sill end caps are used to cap the lower edges of the window frame. Attach the end caps with lower corners using a super glue.

Screw the sill into the uPVC frame

The window frames come with screws that are to be inserted in the holes of the sill. Tighten up the screws using a screwdriver.

Seal the window sill ends with silicone caulk

Sometimes, water accumulates in the gaps between sill and frame. Fill these gaps using silicone caulk. 

Fitting the frame to the opening:

Once you’ve fixed the sill to frame and have filled all the gaps, it is the time to fit the frame into the opening space. 

Install the glass:

Hoist the new window frame into the wall opening

Insert the window frame into the wall with the help of another person. hammer the plastic packers to level the frame in the wall. Use a chisel to break off all the packers coming out of the edges.

Measure and drill fixing holes into the sides of frame 

Mark 15 cm from top and bottom on both left and right sides of the window. Similarly, mark the 60 cm from left right on both top and bottom sides of the window. Then, make holes on the marked points using a drill.

Squeeze a bead of silicone into the holes on the bottom of the frame

Insert silicone caulk on the lower holes to seal them to prevent the entry of water in the window bottom. 

Drill the fixing screws through the frame into the wall

Drill the screws of the frame into the wall and tighten them precisely. But, do not overtighten the screws in the frame. Because it may damage the window frame permanently.

Seal the frame:

Snap glazing platforms into the inside sash edges

Insert glazing platforms into the panels before inserting glass itself. It’ll help you to properly fit glass into panels.

Insert the glass panels into the frame

Now, insert glass panels into the frame opening where it perfectly fits in. Press the glass to fit the window accurately.

Hammer the beads into each sash

Now, hammer the bead into the edges of the glass frame and sash at the top, bottom, and sides of the sash.

Run caulk between the frame and internal wall

Insert a caulk bead between inside of your wall and frame to fill any left gaps.

Insert silicone sealant around the frame’s external surface

Similarly, Insert a caulk bead between outside of your wall and frame to fill any left gaps.

Finish the installation

Finally, you’re finished with fitting your window. You’ve done a marvelous job!


Though, it is not easy to fit a double-glazed upvc window. Because it will require a lot of your effort. But believe me, you can fit it perfectly if you follow all the steps and tips mentioned in this article. Save your money and fit your window by yourself!


 Can I fit the upvc windows in my home by myself?

You can. But make sure that you are registered to FENSA and also buy a window from a well-reputed door and window company.

Can I fit upvc windows from inside of my place?

Yes, you can fit it from either outside or inside of your place. However, professionals recommend you to fit from outside to prevent any damage.

What is the recommended size cavity for double glazing?

16 mm is the recommended size cavity for double glazing windows.

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