Step By Step Replacement Window Fitting

by Editor on April 30, 2013


In the past, many of us were jealous of our neighbours if they sported double-glazed windows. Today, things are very different! With each new house constructed these days, builders install double-glazing as standard. Also, retrofitting double glazing into old houses has become a sizeable industry.

So what is double glazing, you ask? Well, it’s basically two pieces of separate glass that are hermetically sealed with a small cavity (around 4-6mm thick) separating them. If you opt for a larger gap between the two sheets of glass, the benefits of double-glazing (such as greater heat and sound insulation) will be amplified. However, be careful not to go over 300mm as convection currents will result, meaning lost heat!

The glass units and inserted gas have gone through technological advancements across the last 20 years. If your units are particularly dated, you might want to consider upgrading them and lowering your energy bills!

So, if you want to upgrade your own windows and save a fortune in the process, here’s a handy list of what you will need:

  • A tape measure
  • A hammer
  • A nail puncher
  • A good quality scraper
  • Some non-hardening butyl putty
  • Several rolls of good-quality glazing tape
  • Some spacing blocks
  • A handful of beading tacks

Now, let’s go through the window fitting process step by step.

Measuring the Window

Firstly, measure the size of glass you’ll need, from frame border to frame border. Also measure the thickness of the unit. Typically, a 20mm gap will be left between each glass pane. However, variations exist, so measure it up first of all by removing a piece of beading and sliding your measuring tape into the gap.

Plan your Project

If you’re replacing several windows, sketch out a rough drawing of each window with the respective measurements you’ve taken. This means you’ll have a reference of how much glass you require and what measurements you need. When ordering, refer to this list and make sure you tell the merchant that your measurements are border to border (or frame to frame).

Arrange the Window Beading

Arrange  After ordering, you’ll need to sort out the beading. The beading that supports the glass on the frame easily snaps into place. If you have a wooden frame, you’ll need to remove the supporting nails with a nail punch. Some windows conveniently have the beading on the outside (externally glazed) and others have beading on the inside (internally glazed). Wherever it’s located, you’ll need to remove it before installing new windows. Also make sure to lay out the beading on the window shape so it can be refitted later on.

Clear the Surface

If you have wooden window frames, take care to remove any excess fixing compound with your scraper and then carefully give the window frame a good clean with a soft brush.

Placing the Window

Attempt to put in your replacement double glazing into the open window space. If it’s a poor fit, take it back out immediately and check for obstructions. Whatever you do, don’t move on to step 6 until the unit is a snug fit.

Taping the Window

Once the unit is securely in place, it’s time to tape it up! For some added security, you can replace the internal gasket with some strips of good-quality glazing tape. Once in place, this will make the glass nearly impossible to remove without breaking it. If you are installing glass on a wooden frame, opt for non-setting butyl putty instead.

Make sure the glass is central in the frame. Depending on the type of window, you may need to install some spacers at this stage. For example, the glass in opening windows (opening out) needs to be stopped from moving about in the frame. Once you have checked this, give the window a test by opening and closing it slowly. If you have any problems, fine tune the spacer blocks to ensure resolution.

Replacing the Beading

Simply put the plastic or wooden beading back into position and the job is finished! Now, time for a beer!

About the Author

 is a regular blogger who has renovated his own home works on family projects. He spent many years installing Double Glazing in London

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