How to replace a broken glass pane?

Why do glass panes get broken?

There are several reasons why a sash window glass pane may crack or get broken. The most common causes are temperature and humidity changes which lead timber to shrink and swell and affect the glass by its movement.

When the temperature outside fluctuates, over time, this can cause the glass to weaken and eventually break when the minimum force is applied.

replace a broken glass pane

Poor installation can also cause the glass to crack. If the window is not installed correctly, it can put stress on the glass and cause it to break.

Impact. A sharp impact, such as a rock hitting the window or close by tree branches under the heavy wind can bend and broke the glass.

Heritage, hand-blown glass is more fragile

Heritage window glass is much thinner and the surface is inconsistent compared to the glass used in modern windows.

sash window glass pane

In the past, sash windows were often only single-paned and the glass was made using the hand-blown method, so the glass was very thin and used to get broken more often than modern window panes.

Today, most windows are double, triple-paned or even made with tempered glass, so they are much thicker and harder to break.

Modern float sheets of glass that are used for single glazed windows are around 4 mm, while heritage, hand-blown glass could have an inconsistent thickness of 2-3 mm which makes it easy to break, so if you live in one Grade 2 listed property with old Georgian era sash windows, you will find this article handly as most likely you will need to change glass panes quite often.

broken window pane

How to replace broken glass pane in 5 steps

If your window glass pane is broken or cracked, do not worry. This is a relatively easy process that you can do yourself.

Here are the quick 5 steps guide on how to change sash window glass and make it yourself with basic tools and materials:

1. Using a putty knife, gently pry off the old glazing putty. Make certain not to scratch or gouge the wood.

broken glass pane replacement guide

2. Remove any remaining shards of glass from the frame. Use caution not to cut yourself. Removing the broken glass from a sash window pane can be a delicate process. You will need to take care not to damage the surrounding frame or glass.

3. Measure the opening and cut a piece of new glass to size. Make sure to use tempered glass if the window is located near a heat source or in an area where it could be subject to impact.

replace broken window pane

4. Apply glazing putty around the perimeter of the new glass pane. Press it into place and smooth it out with your finger.

5. Allow the putty to cure for 24 hours before painting or staining it to match the rest of the window frame

The job of replacing the broken sash window glass pane is done now.


How much does single pane glass cost?

For the DIYer, single-pane glass is a relatively simple material to work with and can be found at most home improvement stores across the UK, such as Homebase and B&Q and online. The cost per square meter is around £30-40, but most likely, you do not need that much glass, and you can order one pane, cut to measure for £5-10 + delivery cost.

How to cut pane glass?

Take the glass sheet and place it on the table. Draw the line to mark the bit of the glass you want to cut off. Use a glass cutter and score the glass along the line you want to cut. Finally, use caution when breaking the glass along the line.

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