Cat flap fitting in London, into glass that cannot be drilled.
Almost every glass door in London is toughened, and toughened glass cannot be cut. Try it and the whole pane turns to gravel. The correct job is to make a new sealed unit with the aperture already in it, which is exactly what our workshop does.
Why your glazier said no, and the fitter said yes
Glass in a door is a critical location under Building Regulations, so it is almost always toughened or laminated safety glass. Toughened glass is under permanent internal tension. Cut it, drill it, or grind an edge and it does not chip, it detonates into thousands of blunt fragments across your floor.
That is why a handyman who says he can cut your glass door on site is either wrong or is about to replace your glass at your expense. The hole has to go in before the glass is toughened, which means a new pane, not a modified one.
Toughened glass
Cannot be cut, drilled or edged after toughening. The aperture must be cut while the glass is still annealed, then the pane goes through the furnace.
Laminated glass
Two panes bonded to an interlayer. Can be cut, but it is slow, messy work and rarely the cheaper route once labour is counted.
Annealed single glazing
Older single glazed doors can sometimes be cut in situ. Increasingly rare in London, and it may not be compliant to leave it that way.
Sealed double glazed units
The aperture has to pass through both panes and the spacer has to be routed around it. This is unit manufacture, not a site job.
Four steps, one visit each end
We survey, make the unit, and come back to fit. The middle part happens in the workshop, which is why nothing gets drilled in your hallway.
| Step | What happens | Where |
|---|---|---|
| 1. Survey | We measure the existing unit, confirm the glass type and check the cat flap model's exact aperture. Bring us the flap or the box if you already have it. | Your door |
| 2. Manufacture | A new sealed unit is made to the same size with the aperture cut before toughening, then the unit is sealed around the hole. | Our workshop |
| 3. Fit | Old unit out, new unit in, beads back, cat flap fitted and sealed into the aperture. | Your door |
| 4. Check | Flap swings clean, seals close, and the door still locks and closes on its gaskets as it did before. | Your door |
What we can and cannot put a flap into
Glass doors and side panels
New sealed unit with the aperture in it. The most common job, and the one most people are told is impossible.
uPVC doors, glazed panel
Same approach. If the door has a solid infill panel instead of glass, the flap goes through the panel, which is a simpler and cheaper job.
Patio and bifold doors
Yes, though on a sliding door the flap normally goes in the fixed pane rather than the moving one, so the mechanism is untouched.
Composite and solid timber doors
This is joinery, not glazing. We will tell you straight if a joiner is the better call rather than take the booking.
Aperture sizes are set by the cat flap, not by us. Most microchip flaps want a circular hole around 212mm across and larger pet doors nearer 265mm, but it is model specific and we confirm it against your exact unit before anything is ordered. Ordering glass to the wrong aperture is an expensive mistake and it is entirely avoidable.
The replacement unit still has to be safety glass
Glazing in a door, and within 300mm of a door edge up to 1500mm high, is a critical location. The replacement unit has to be toughened or laminated to BS 6206, exactly as the original was. A cat flap does not change that, and anyone offering to put ordinary float glass in your door to make the cutting easier is creating a hazard.
We make the unit to the same safety specification as the one that came out, and we will put the spec in writing if your building manager or insurer asks for it.