Why can't existing toughened glass be cut?
Toughened glass is heat treated so that internal stresses make it stronger and change the way it breaks. Those stresses are also the reason you cannot simply drill a circular cat-flap hole into an already toughened pane. Trying to cut or drill it after manufacture can cause the whole pane to shatter into small fragments.
For technical background, see Pilkington Toughened Glass, which notes that cutting and drilling must be completed before toughening.
How is new cat-flap glass made?
What if it is double glazing?
The same principle applies, but the job usually involves replacing the complete sealed unit rather than one loose pane. The new double-glazed unit is manufactured to match the opening, with the pet-flap cut-out built into the specification from the start.
Read our full guide: Can you install a cat flap in double glazing?
If you have not chosen the flap yet, compare our microchip cat flap options for glass doors before the replacement glass is ordered.
What if it is single toughened glass?
If the existing single pane is already toughened and has no suitable opening, it still cannot simply be drilled afterwards. A new pane is normally measured and ordered with the required cut-out completed before toughening.
How do I know whether my glass is toughened?
Look near the corners of the pane for a permanent safety-glass stamp or etched marking. If you cannot identify the glass, send us a clear photo of the full door or window and close-ups of any visible markings. We can then advise on the likely installation route.
Choose the cat flap before ordering the glass
This is important. Different manual, microchip and smart cat flaps can require different hole sizes, adapters and tunnel arrangements. The flap model should normally be confirmed before the replacement glass is manufactured so the opening is made correctly.
How much does a cat flap in toughened glass cost?
Our suitable straightforward door or panel cat-flap installations can start from £95, but toughened glass and double-glazing jobs are quoted separately because they require made-to-measure replacement glass. The size of the pane, glass specification, sealed-unit construction, pet-flap model and access all affect the final price.
See our cat flap installation cost guide for more detail.
Can you install the flap in a door instead?
Sometimes a suitable uPVC, composite or timber panel can be a simpler route than replacing glass. If your door has both a panel and a glazed section, send photos of the whole door and we can compare the options. See our uPVC vs composite door cat flap guide.
Frequently asked questions
Can a glazier drill a hole in existing toughened glass?
No. Toughened glass is normally processed before toughening and should not be drilled afterwards.
Will toughened glass shatter if you try to cut it?
It can. Cutting or drilling disturbs the internal stress pattern and can cause the pane to break into many small fragments.
Can you fit a microchip cat flap into toughened glass?
Yes, provided a suitable replacement pane or sealed unit is manufactured with the correct opening for that model.
Can I keep my old glass?
If you want the old pane or sealed unit retained after removal, tell us before the visit so we can confirm whether this is practical and safe for that job.
Need a cat flap fitted into glass?
Send us a photo of the full door or window, any safety-glass markings, the flap model and your postcode. We can advise on the correct replacement-glass route and provide a quotation.
For fitting, see our Cat Flap & Dog Flap Installation London service page. For safety-glass replacement generally, see Toughened & Safety Glass London.