A flap open for the cat: What to keep in mind when installing a cat flap

From different types of cat flaps, to the correct placement, to installation: Learn everything you need to know when installing a cat flap in your home in this article.


Cat jumps through a cat flap in the door

Close your mouth... now open it. An everyday orifice, bigger in some of us, smaller in others. And there we have something in common with the entrance portal for our stubborn housemate - the cat. Many people prize them as pets because of their independence. Needless to say, though, it’s a double-edged sword. Bang goes your well-deserved sleep late at night when velvet paws scrape razor-sharp claws over freshly polished panes with a heart-warming yowl. She wants to get in. But human doors won’t cut it. What your cat needs is its own door, a cat door. Or to be precise, a cat flap.

Invented by the eminent Sir Isaac Newton, no less, at the end of the 17th century, cat flaps have steadily caught on ever since. And not only have they become more popular, they are also no more technologically sophisticated. Nowadays, they cover the whole gamut, from a simple hole with a flap to a high-tech door with a built-in time portal. Well, slight exaggeration perhaps, but read on to make sense of the numerous options out there to let cats and tomcats in or not, how to install them and what questions you should ask in the process.

Wide-ranging cat flap types

A tough lesson, which some of you may have learnt the hard way. Having a large flap isn’t always the best option and sometimes it is simply better to keep it closed. Following, an overview of how to determine the optimal size for your cat flap and what closure options you have on the market.

How large should the flap be?

You don’t want your cats and tomcats busting a gut to get in and out each day - the flap should be big enough for them. But not bigger than you need. The bigger the flap, the greater the impact of the weather outside or the risk of unwanted guests coming in. For those in the mountains in particular, ensure the size of the flap is a few safety centimetres below the minimum wolf size. A good rule of thumb when dimensioning the cat flap is the size of the cat plus 3 cm on all other sides.

  • Tip: Channel the inventive magic which led to the cat flap and try this experiment. Cut a hole of the desired size and shape in a piece of cardboard and let your cat hop through.

How best can you keep the flap closed?

For ecological, safety and territorial reasons, your cat flap must - of course - be lockable. But here too, there is more than one way to do so.

Cat flaps featuring a 2- or 4-way closure can be opened on both sides like small swing doors. Choose the latter, though, if you want the most flexible option and then you can configure the way it opens and closes depending on direction:

  • Fully open

  • Only open from outside

  • Only open from inside

  • Fully closed

However, conventional 4-way models don’t just offer your cat all these options, but all other animals of this size too. Hence the range of systems outlined below, which can only be unlocked with certain aids:

  • Magnet: A magnet on the collar of the cat or tomcat opens the mechanism.

  • Infra-red: An infrared transmitter on the cat's collar unlocks the flap by radiation signal.

  • Chip: An implanted chip transmits the identity of your cat to the flap. Ingenious extras:

  • Intelligent cat flaps make it a breeze to define the opening hours via app.

  • The most advanced cat flaps have a sensor that can leverage AI to detect whether your cat is bringing home a hunting trophy and deny it entry if necessary.

  • Some cat flaps are insulated to help prevent draughts or cold spots, keeping both kitty and you more comfortable.

Placing the cat flap

Once you’ve decided on your cat flap model of choice, the only decision left is where best to position it. And here, weighing up a few different things makes sense. On the one hand, the flap should not be exposed to the weather. Conversely, however, the entrance should be easily accessible for your cat and in a familiar place, so they can start using it right from the get-go without any learning curve. Finally, with the need to save energy in mind, such flaps are best installed in unheated rooms to avoid any unwanted heat loss. In general, however, most cat flaps can be built into windows, doors or even brickwork.

Installing a cat flap in a window or balcony door

Installing a cat flap in a window or balcony door couldn’t be easier. As a rule, new window glass is supplied directly with the appropriate cut-out, which means that if you no longer need the cat flap, the original glass can be conveniently reinserted.

If you can’t purchase the cat flap with a matching windowpane, installing it may be a little more challenging. Leaving it to an experienced manual worker is your best bet.

Installing a cat flap in the door

Installing your cat entrance in a solid wood door should be no problem and just a question of sawing the desired recess out of the door. Keep in mind, however, that reinserting the piece is not as easy as with a window. And if your door has multiple layers (e.g. thin plywood and a cardboard interior), it becomes trickier still. In this case, you are probably best off rethinking the installation and trying to find a more suitable place.

Installing a cat flap in brickwork

From an aesthetic perspective, installing a cat flap directly into masonry is certainly the most elegant option. That said, installing it on an existing building is very complex and can lead to complications like cold spots or leaks. Ideally therefore, the cat flap should be included in the planning when building or renovating your home.

Assembling the cat flap

Experienced DIYers can also have a go at installing the flap themselves. Here are a few tips if you opt to do so:

  • To install the cat flap, have a tape, tape measure, drill, cordless screwdriver, jigsaw and pencil to hand.

  • The easiest way to do this is to lift the door or window of choice off its hinges.

  • Choose the right height and placement: Ideally 15 cm or so above ground, depending on how big your cat is. When installing in a door, you should also ensure that the cat flap does not obstruct it opening and closing in any way.

  • Most cat flaps come complete with a template for installation. Use adhesive tape to fix this in the desired position and drill the holes.

  • For wooden doors: First off, check whether your door can handle this kind of installation. Solid wood or pressboard doors are perfect. Light wooden doors made of thin plywood boards and cardboard interiors, conversely, may break while the cat flap is being installed. The template shows you where to drill the holes. Drill in the marked places, connect the drill holes with horizontal and vertical lines and simply saw along them. To attach it yourself, simply follow the assembly instructions.

  • For glass doors and windows: a drill and saw will be of little use here. You will need glass cutters and special glass glue instead.

But be careful: For glass doors in particular, installation should be left for the most advanced DIYers! If in doubt, seek professional help.

A cat bell as a cat flap alternative

If all this seems over the top or if your kitty wants a more sophisticated option, the cat bell offers an elegant intermediate solution. You are notified of your cat's wish to enter by a light or acoustic signal. The presence of the cat is detected by a pressure sensor or an infrared barrier at the entry point. Here, too, there are models that signal every movement and ring the bell, but there are also models with a chip and infrared that only signal when your cat enters.