UPVC double glazing

UPVC windows and doors are becoming far more fashionable in homes around the UK these days. They are stronger and more resilient than other types of materials and also conserve energy. Fitting double-glazed UPVC windows can be costly though, so shrewd DIYers thinking about doing it themselves can actually save a fair bit of money by doing so.

Level of difficulty

Level 2: Medium

What you need

Double glazing units
Glazing tape
Spacing blocks
Beading tacks


Getting the right size of window off the bat will mean not having to make changes to the walls, which would add a sizeable amount of time and effort to your job.
Start your task by accurately measuring the size of the glass panes and frames that you currently have installed, both inside and out. This will mean that when you order with the glass merchant you can get something that fits snugly and you will not need to make any adjustments.

Removing old windows

Start by removing the glass from your old frames. If they have been double glazed already. This should be easy enough, but it will be a little harder with older windows. For double glazing, simply peel away the seals that are holding the windows in place, starting with the bottom and then the two sides. Always support the glass before removing the top seal ,after which the pane should just lift out with some manipulation.

With older windows, you will need to use a scraper to remove the putty holding the pane in the frame.

  1. Start at the bottom and work your way along the two sides before supporting the glass and working on the putty along the top of the pane.
  2. Removing the frames can be tricky. If you try to do it all in one go, you will risk damaging the walls, which you would need to fix. To get around this, simply use a saw to cut the frame into pieces, removing it bit by bit.
  3. Unscrew all of the screws holding the frame in place and then carefully chisel it away from the wall to allow you to lift it out piece by piece.
  4. Use your chisel to get rid of any old protrusions or cement left in the opening you now have to make the fitting of the new window much easier.

Fitting a UPVC frame

If you will be attaching a window sill, start by sitting this onto the brickwork at the bottom, using a saw to gently trim the side protrusions if need be to make sure everything sits in place perfectly.

  1. Use plastic packers to make sure the window sill is level, with the slightest gap between it and the brickwork. Check everything is straight with a spirit level and then screw the sill into the brickwork with provided screws. It is important not to overtighten these, as the plastic can easily split.
  2. Hold the window frame in place along the up stand part of the window sill and ensure that it sits on the protruding beading.
  3. Use silicone to attach the window to the beading and then wipe away any excess to ensure a clean finish. Then make use of your spirit level to make sure the window is straight all the way around. Have someone hold it while you do this.
  4. Starting at the bottom of the window, use screws provided to attach the frame to the sill, taking care not to overtighten.
  5. Once it is attached at the bottom, you will need to drill through the sides of the frames all the way around into the brick work to make holes for attaching the window frame to the wall.
  6. Carefully hammer the fixers around the frame into your drilled holes and then screw these onto the brickwork. Again, do not overtighten as you can break or warp your frame by doing so.
  7. To fit the panes, start by fitting glazing bridges in the gaps where the glass will be sitting.
  8. With help, hold the glass in its place in the frame. You will need to use the rubber seals provided to hold it there. Starting at the top, press these into the correct gaps and go along with your thumb, ensuring they sit snugly into the correct gaps.
  9. Both inside and outside the window, use a silicone gun to fill any gaps between the walls and the window frame to stop the draught from breaching. Then all you will need to do is allow everything to set in place.


Take care with screws. UPVC will bend and warp and eventually break if screws are overtightened throughout the job.


Glass and window frames are heavy. Always have someone on hand to help you with lifting and holding everything in place. It will be a lot harder to complete the task alone and you will risk injury.

Please note that all our DIY guides and ‘Expert answers’ advice have been written strictly for reference only. Rated People do not accept any liability for any damage caused to an individual, property or anything else as a result of following our DIY guides and using our ‘Expert answers’ advice.

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