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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:
- Order factory‑prepared routing for your chosen flap; or
- 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
- Free survey (Andover & across Hampshire): confirm door type/panel, measure IGU if glass, agree location.
- If glass: we order a new toughened sealed unit with factory cut‑out.
- 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
No. Toughened glass cannot be cut after manufacture. We replace the pane with a new toughened unit made with the hole.
Often yes if cut after installation. Some manufacturers will accommodate a factory‑prepared opening—ask us and we’ll check your specific door
Usually into the fixed pane using a slimline model so the slider still clears
Yes. It reads your pet’s microchip to keep out intruders
Not for a glass‑only unit swap. FENSA covers full window/door replacements with frames, not repairs.
Any aperture is a potential weak point. Keep keys distant and consider internal guards; police advice specifically warns about “fishing” through openings
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.
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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