Cat flaps in uPVC, composite & glass doors: what’s possible (and what isn’t)

Cat flaps in uPVC, composite & glass doors: what’s possible (and what isn’t)

Yes—cat flaps can go in most uPVC panels and in glass doors/patios, but the glass unit must be replaced with a new toughened pane pre‑cut for the flap (you can’t cut existing toughened glass). Composite doors are case‑by‑case and often need factory prep, otherwise you risk voiding the warranty.

Quick guide: where a cat flap can go

• uPVC doors (solid/panelled): Usually fine; we install into the lower uPVC panel or supply a new panel cut for the flap.
• Glass in doors or patios (double‑glazed): We replace the sealed unit with a like‑for‑like toughened pane manufactured with a hole for the flap. You cannot cut an existing toughened unit. in.saint-gobain-glass.com
• Sliding patio doors: Typically the fixed pane gets the flap; slimline flaps maintain sliding clearance. petflapsuk.com
• Composite doors: Often voids the slab warranty if you cut after installation; best ordered factory‑prepared or we’ll advise alternatives.
• Fire‑rated doors (e.g., flat entrance / garage internal): Don’t do it—modifying a fire door compromises certification. Sure Petcare explicitly warns against fitting flaps in fire doors. manualslib.com

uPVC doors: the straightforward option

For most uPVC front/back doors, we fit the flap in the lower solid panel, keeping clear of reinforcement and lock areas. Expect a neat finish, draught seals intact, and no drama. If the panel is decorative or too thin for a secure clamp, we’ll swap it for a new matching panel pre‑cut for the flap.

Good to know: Choose a mounting height that lets your cat walk through level with their belly; most manufacturers advise “as low as practical” if features dictate.

Glass & patio doors: don’t cut—replace the unit

Double‑glazed doors and side panels use toughened safety glass. After toughening, glass cannot be cut or drilled; the hole must be created before the glass is toughened and the new sealed unit manufactured. That’s why our process is: survey → order new toughened IGU with factory hole → fit → install flap with a proper adaptor.

For sliding patios, we generally fit into the fixed pane and use a slimline flap so the sliding leaf still operates.

Composite doors: proceed carefully

Composite slabs are layered (GRP skin + core). Cutting them post‑install can reduce insulation, introduce water ingress points, and invalidate the door warranty with many brands. Two safe routes:

1. Order factory‑prepared routing for your chosen flap; or
2. Use a wall/glass installation instead.

Several UK door makers and installers state that DIY or post‑fit cat flaps invalidate warranties—speak to us first and we’ll advise on manufacturer‑approved options.

Security & insurance: sensible precautions

• Key‑fishing is real. UK police guidance warns thieves can fish car/house keys through openings like letterboxes—and even cat flaps in some cases. Keep keys well away from the door; consider internal guards where appropriate. police.uk
• Microchip flaps help by keeping out strays/foxes (selective entry). Sure Petcare’s microchip flaps are built for this. surepetcare.com
• Locking & cylinders. Pair the flap with good practice: engage your multi‑point lock, consider a split‑spindle/auto‑locking setup, and don’t leave handles operable from inside reach.

Building regs, FENSA & paperwork (don’t overthink it)

• Glass‑only swap FENSA. FENSA covers replacement windows/doors (frame included). Repairs like replacing a glazed unit only are not covered—so don’t expect a FENSA cert for a cat‑flap glass swap. Doors with <50% glazing are often outside FENSA scope too. fensa.org.uk
• Fire doors. If your door is fire‑rated (flat entrance or internal garage door), do not install a flap—manufacturer‑approved assemblies only. Sure Petcare manuals explicitly prohibit fitting to fire doors; government guidance underscores maintaining door integrity.

Which cat flap?

• Microchip (our default recommendation): lets your pet in, keeps others out; add wall/glass adaptors as needed.
• Manual 4‑way (budget): simple, with in/out/locked settings and basic draught control.

Our process in Hampshire

1. Free survey (Andover & across Hampshire): confirm door type/panel, measure IGU if glass, agree location.
2. If glass: we order a new toughened sealed unit with factory cut‑out.
3. Installation: fit the new unit/panel and install the flap with the correct mounting adaptor; test operation; tidy up.

Service areas: Andover, Winchester, Basingstoke, Salisbury, Newbury, Southampton, and surrounds.

Cat-flap FAQ

Get a quote

Thinking about a cat flap?
Send us a quick photo of your door (inside & outside) and, if glass, the bead type and unit thickness if known. We’ll confirm feasibility and give a firm price.

[email protected]

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Mark Pearce

With over four decades in the glazing industry, Mark Pearce has been at the heart of KJM Windows & Conservatories since 1983. Starting as a building labourer, he quickly rose through the ranks, working as a window and door installer from 1984, a factory operator manufacturing windows later that year, factory manager in 1992, and joining the sales team in 1994. Becoming a Director in 2002, and finally, the sole owner in 2010, Mark Pearce is truly a double glazing expert and has led KJM to become a leading supplier of high-quality windows, doors, and conservatories across Andover and the South of England.

Mark Pearce is a highly experienced specialist in the double glazing industry, having built his knowledge from the ground up through hands-on experience in installation, manufacturing, sales, and business management. Beyond his role at KJM, Mark is a keen blogger, writer, and traveller, often sharing insights on the latest innovations in the home improvement industry.

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