Cat Flap Installation in Glass and Sealed Units

Double glazing is an assembly with a sealed cavity between panes. Making an opening in an installed unit would interrupt that assembly. Toughened safety glass also cannot simply be cut after manufacture. The glass specification and the flap opening therefore have to be planned as part of making the replacement unit.

For the way a complete glass assembly is replaced while its frame remains, see sealed unit replacement. A cat flap opening changes the specification of that replacement; it does not mean the whole door must be replaced. The surrounding frame still needs to be suitable to hold the new unit securely.

Different flaps need different openings, adapters and fixing arrangements. The dimensions of the flap's outer body are not necessarily the dimensions of its required hole. Providing the actual fitting information avoids ordering glass around an assumed size and discovering that the selected flap does not fit afterwards.

Discuss the intended position as well as the flap itself. There must be room for its fittings and for the door to operate normally. If you have not chosen a model, explain that before the glass is specified. We make no claim about fitting particular brands; compatibility is assessed from the proposed product and the glazing arrangement.

A glazed entrance, patio door and fixed side panel are not interchangeable locations. Their panes, beads and clearances differ, and glass in doors or low positions has safety requirements. Where a door already has a glazed cassette, the way that cassette is retained is part of the assessment.

Our door glass replacement page covers retaining a sound door while its glazing is changed. For a cat flap, the available space must also suit the prepared opening. We check the existing installation rather than suggesting that any pane, in any position, can accept a flap.

Once the dimensions and specification are agreed, the new unit is made with the opening. The old unit is removed and the replacement is fitted into the frame with suitable support and retained by the existing glazing arrangement where appropriate. The flap is fitted to the prepared opening according to its requirements.

The quote reflects the glass size and specification, the required opening, the fitting arrangement and access to the glazing. There is no fixed price here because those details have not yet been checked. Send a picture of the whole door or panel and the flap information, then request an in-person quotation. Do not try drilling or cutting the existing glass while waiting for advice.