Why the glass has to be replaced
A sealed unit is two or more panes held apart by a spacer and sealed around the edge. Drilling through it would break that seal and, with toughened glass, shatter the pane. Instead, a replacement unit is made to the same size as the existing one, with a round hole through both panes and a sealed collar around the opening so the unit stays airtight.
Because the new unit replaces the old glass rather than altering it, the frame, door or window stays exactly as it is. The work is a form of glass replacement; our window glass replacement page explains how panes are measured and changed in general.
Where a double glazing cat flap can go
Common positions are the glazed panel of a back door, a patio door pane, a side panel next to a door or a low window that opens onto a garden. The pane needs to be large enough for the flap with a sensible margin of glass around it, and low enough for your cat to reach comfortably without a long jump.
Think about what is on each side. A flap that opens onto a busy path, a drop or a spot where the cat will be stranded in rain is less useful than one leading to a sheltered patio. Also consider furniture inside: a flap behind a sofa or into a utility room may suit the household better than one in the main living space.
Choosing the flap
Cat flaps for glass are designed with a mounting collar long enough to pass through a double glazed unit. Basic flaps swing freely; others have locking settings, and microchip models open only for registered pets, which helps keep neighbouring cats out. The flap you choose sets the hole size, so decide on it before the new unit is ordered.
Larger dogs need a bigger opening and a bigger pane. Battery or mains power, ease of cleaning and how noisy the flap is are worth comparing too. If you are unsure, having the flap to hand at the survey means the hole can be specified to suit it exactly.
Composite doors with cat flap options
On composite and uPVC doors, the glazed panel is often the simplest place for a pet door, because cutting the solid door slab can affect its structure and finish. Where a door has no suitable glass, a flap may need to go elsewhere, such as an adjacent side panel or window.
If you are replacing a door anyway, it is worth planning the pet door at the same time, so the glazed panel is specified with the flap hole from the start. Our composite doors page sets out the door styles and glazing options.
Fitting and what to expect
The process normally involves two visits: one to measure the existing pane and agree the flap position, and another to fit the new unit once it has been made. On the day, the old glass is removed, the new unit with its opening is glazed in, and the flap is installed and checked.
Fairway Window Systems Ltd offers a free home survey and written quote. Use the existing enquiry form to say which door or window you have in mind and which flap you want to use, so the right unit can be planned.
Frequently asked questions
Can you cut a hole in existing double glazing for a cat flap?
No. Sealed units and toughened glass cannot be cut once made. A new unit is manufactured with the hole already in it and fitted in place of the old pane.
How long does fitting a cat flap in glass take?
The pane is measured first and the new unit is made to size, so there is a wait between visits. Fitting the unit and the flap on the day is usually a short job.
What affects the cost of a cat flap in glass?
The size and type of the pane, the glass specification, the hole size for the chosen flap and the flap itself.
Can I keep my existing cat flap?
Often, if its collar is long enough for a double glazed unit. Bring it to the survey so the hole size can be matched.