Cat Flap & Glazing Glossary
Plain-English definitions for every cat flap, door and glazing term we use in quotes and on the rest of the site. Written by working UK installers — no marketing fluff.
Toughened glass
Heat-treated safety glass that is 4–5× stronger than standard glass and shatters into small, blunt fragments. Required in doors and low-level windows under Approved Document K. Cannot be cut after manufacture — any aperture (including for a cat flap) must be pre-cut at the factory.
Laminated glass
Two panes bonded with a clear plastic interlayer (PVB). Holds together when broken, so it stays in the frame. Often used where extra security is required or where toughened isn't suitable.
DGU (Double-Glazed Unit)
Also called a sealed unit or IGU. Two panes of glass separated by a spacer bar with desiccant inside and sealed at the edges. The whole sealed unit is what we replace when fitting a cat flap into a glass door — your frame is untouched.
Spacer bar
The metal or warm-edge strip around the perimeter of a DGU that holds the two panes apart and contains desiccant to prevent internal misting. Usually stamped with the manufacturer date and toughened/laminated marking.
U-value
A measure of how much heat passes through the glass. Lower = better insulation. UK Building Regulations (Approved Document L) require replacement units to hit 1.4 W/m²K or better for double glazing.
WER (Window Energy Rating)
A–G energy efficiency rating for whole windows. Band C is the minimum for replacements under Part L.
Microchip cat flap
A flap that reads your cat's existing identification microchip (or an RFID collar tag) and only unlocks for registered pets. Stops neighbour cats, foxes and strays getting in. SureFlap, PetSafe and Cat Mate all make microchip models.
DualScan
SureFlap's premium model that scans the chip on the way out as well as in — letting you keep certain cats indoors while others have free access. Useful for multi-cat households or post-surgery recovery.
4-way locking
A manual cat flap mode found on most brands: in only, out only, fully open, fully locked. Standard on every PetSafe Staywell and Pet-Tek model.
Cat flap aperture
The cut-out in the door or glass that the flap mounts through. We measure this precisely before ordering glass — even a few millimetres off and the flap won't seal properly.
Rise (or step-over)
The vertical distance from the floor inside the cat flap tunnel. Recommended UK heights are 100–150 mm for healthy adult cats, lower for kittens, seniors or arthritic cats.
Tunnel extender
An accessory that lengthens the flap's tunnel so it fits through thicker walls, composite door slabs or insulated panels. SureFlap, PetSafe and Pet-Tek all sell their own.
Intumescent strip
An expanding fire-resistant seal fitted around fire doors. We don't fit cat flaps into fire doors — it would compromise the strip and the door's fire rating.
Beading
The plastic, timber or aluminium trim that holds the glass unit into the frame. Removed and re-fitted when we swap a sealed unit — usually internally beaded for security.
Internally beaded
A door or window where the beading is on the inside, meaning the glass can only be removed from inside. The UK standard for security since the early 2000s.
Composite door
A door made from a layered GRP or timber skin over a solid insulating core (often 44–48 mm thick). Solidor, Rockdoor and similar. Needs a tunnel extender on most cat flap models.
uPVC door
An unplasticised PVC framed door, often with a glass or plastic panel. Panels can usually be swapped for one with a pre-cut cat flap aperture, or the flap fitted directly into a thinner solid panel.
Bi-fold door
Folding glazed doors that concertina open. Cat flaps can be fitted but only into a non-traffic pane (so the flap doesn't get crushed when folded). See our bi-fold cat flap guide.
Sliding patio door
Two or more glazed panels where one slides past the other. We fit cat flaps into the fixed pane only — see our patio door guide.
French doors
A pair of outward-opening glazed doors, often used between a kitchen/living area and the garden. Cat flap goes into the non-active leaf.
FENSA
Fenestration Self-Assessment scheme — certifies replacement of whole windows and doors against Building Regulations. **Not** required for cat flap installs in glass, which are classed as repairs. See our FENSA explainer.
CERTASS
Alternative competent-person scheme to FENSA. Same scope (whole window/door replacements) — also not required for glass-only swaps.
Building Regulations Part K
Approved Document K — the part of UK Building Regs covering safety glazing. Glass in doors, beside doors, or below 800 mm in windows must be toughened or laminated.
Building Regulations Part L
Approved Document L — energy efficiency standards. Sets the minimum U-value for replacement glass units.
RFID collar tag
A small disc on your cat's collar that some flaps read instead of (or in addition to) a microchip. Useful for cats whose chip has migrated and can no longer be read reliably.
ISO FDX-B chip
The international 15-digit microchip standard used in the UK and Europe. Every cat flap microchip reader on the UK market reads this standard.
Battery flap vs hardwired
Domestic microchip flaps are battery-powered (typically 4× AA, 6–12 month life). Hardwired flaps don't exist for the consumer market — anyone offering one is likely mis-selling.
Manual flap
A non-electronic flap with a magnetic catch and a 4-way slider lock. Cheapest, simplest, no electronics to fail. Standard for single-cat households without stray problems.
Brush strip
Weather seal around the flap perimeter that blocks draughts. The first thing to check if a flap gets noisy or starts letting cold air in.
Pet-Tek (formerly Dogwalk)
UK manufacturer of heavy-duty cat and dog doors known for the silent magnetic close. The brand was rebranded from Dogwalk to Pet-Tek.
Term not listed?
Ask a real fitter — we'll answer within a working day and add it to the glossary.