Cat Flap in a Glass Door: The Complete UK Guide (2026)

If you've got a glazed back door, French doors, a patio slider or a conservatory, you've probably already discovered that cutting your existing glass isn't an option. Don't worry — there's a clean, tidy way to get a cat flap into almost any glazed door in the UK, and we do it every week across the North West.

No — and any installer who says otherwise should be a red flag. Modern UK doors are fitted with toughened (tempered) safety glass. Toughened glass is heat-treated so that if it breaks, it shatters into thousands of tiny blunt pieces rather than dangerous shards. The trade-off is that it cannot be cut, drilled or modified after manufacture. The moment a cutting wheel touches it, the whole pane explodes.

The solution is simple: we order a brand-new toughened glass unit with the cat flap aperture cut in at the factory, then swap it into your existing frame. Your door looks identical — it just has a neat circular or square hole sized exactly for the flap.

We routinely install into:

• uPVC back doors with a single glazed panel • French doors (one or both leaves) • Sliding patio doors (aluminium or uPVC) • Bi-fold doors • Conservatory side panels • Composite doors with a glazed insert • Sash and casement windows with a fixed lower pane

What matters isn't the door material — it's the glass unit inside it. As long as we can measure the sealed unit, we can replace it with a pre-cut version.

1. You send photos and rough measurements via our quote form or WhatsApp.
2. We confirm the unit is double-glazed toughened (it almost always is) and give you a fixed price.
3. We attend on day one to take precise factory measurements — width, height, glass thickness, spacer bar, any internal grids.
4. The new unit is manufactured to order (usually 10–14 working days for clear glass, longer for obscured or patterned).
5. We return on day two, remove the old unit, fit the new pre-cut unit, install your chosen cat flap, seal and silicone everything, and clean up.

Total disruption: around 90 minutes on the install day. Your door is fully usable and secure the whole time in between.

Glass installations start from £280. The final price depends on:

• Glass size and thickness (most domestic units are 4–28 mm) • Whether the glass is clear, obscured, low-E, laminated or has Georgian bars • The cat flap model you choose (manual, magnetic, microchip, dual-scan) • Your location within our service area

For most standard back doors with a SureFlap Microchip Pet Door, you're looking at £320–£400 all-in. There are no hidden extras — the quote we send is the price you pay.

Any flap will fit a glazed unit because we cut the aperture to suit. The most popular choices our customers go for are:

• SureFlap Microchip Cat Flap — the everyday favourite. Reads your cat's existing vet chip. • SureFlap Microchip Pet Door — same tech, larger flap, suits Maine Coons, Ragdolls and small dogs. • PetSafe Staywell 400 — budget-friendly manual flap with 4-way locking. • Pet-Tek Glass Fit — designed specifically for glass, very low profile.

If you're unsure, our Will-It-Fit tool and Cat Flap Quiz will narrow it down in under a minute.

A good install is airtight. We use butyl tape and silicone around the flap frame, and modern microchip flaps include magnetic seals on the inner and outer flap. Customers regularly tell us they can't feel any difference in heat loss compared to before the flap went in.

If you're worried about draughts, the SureFlap Dual Scan and the PetSafe Microchip flaps have the tightest seals we've measured.

From first message to fitted flap is typically 2–3 weeks, almost all of which is the glass manufacturing lead time. The two visits themselves take about 30 minutes (measure) and 90 minutes (install).

Generic glaziers can swap a glass unit, and generic handymen can fit a flap into wood or uPVC — but a cat flap in a glass door sits at the intersection of both trades. Getting the aperture position right (height for your cat, clearance from the frame, alignment with the handle), specifying the correct glass spec, and handling the manufacturer's tolerances takes experience. We've done thousands of these specific installs and carry a 3-year workmanship guarantee on every one.

Ready to get a price? Send a couple of photos through our quote form and we'll come back within a few hours with a fixed quote.