Guide · · 4 min read
Internal cat door: for the laundry, the garage or a litter room
An internal cat door lets you close the laundry, garage or spare room and still give the cat its litter tray. The one thing to check first is how thick the door is.
By the Pet-Tek International team, Auckland — designers of Catwalk® and Dogwalk® since 1999.
Not every cat door leads outside. Some of the most useful ones go in an ordinary inside door: the laundry where the litter tray lives, the garage the cat sleeps in, or the spare room you want to keep warm and closed. You get the door shut, and the cat still gets through.
Why fit a cat door inside the house
- The litter tray room. Keep the laundry or bathroom door closed, keep the smell in, and keep toddlers and dogs out of the tray.
- The garage. A cat that sleeps in the garage or uses it as the way out to the yard.
- Heating. Close a heated room or the hallway door in winter without shutting the cat out.
- Keeping the dog out. Cat food and litter on one side, dog on the other.
Step one: measure the door’s thickness
This decides the model. Open the door and measure across its edge with a tape measure.
- 11–30 mm: the Catwalk® Wood-Fitting Cat Door (Slim Line) fits.
- Over 30 mm, up to 52 mm: the Catwalk® Wood-Fitting Cat Door Tunnel. Many internal doors are around 35–40 mm, so this is the one most people need inside the house.
Both have the same 155 × 157 mm opening for cats up to about 7 kg, a brush seal and the factory-fitted 4-way lock.
Hollow-core doors
A lot of inside doors are hollow-core: two thin skins over a light timber frame with a honeycomb or air gap in the middle. Cutting one open leaves the cavity showing. The tunnel model solves this: its self-adjusting tunnel lines the cut-out from one skin to the other, so the hole looks finished from both sides and nothing can crawl into the door.
Keep the cut-out inside the solid frame that runs around the edge of the door. Tap along the bottom of the door: the solid frame sounds dull, the hollow centre sounds hollow. Mark the cut-out in the hollow area, above the bottom rail, so the door keeps its strength.
Where to put it
The bottom of the opening should sit at the cat’s belly height, usually 100–150 mm above the floor, so the cat steps through instead of climbing. Centre it on the door, away from the handle and hinges. On a laundry door, check the flap will not hit the washing machine or the tray when it swings.
How to fit it
- Take the door off its hinges and lay it flat on a bench or two trestles. It is much easier than cutting it upright.
- Tape the template from the box in place and drill a hole in each corner.
- Cut along the lines with a jigsaw, keeping the blade square.
- Fit the frames from each side (and the tunnel, if you have that model), then screw them together.
- Rehang the door and turn the dial through all four positions.
It is a typical one-hour DIY job. Our wooden door guide walks through the cutting in more detail.
Keeping the dog out
The standard cat opening is too small for most dogs. If yours is small enough to squeeze through, the Catwalk® Multi-Magnetic is the answer: the flap stays latched until a cat wearing the small collar magnet walks up to it. No batteries, and it fits doors from 11 to 52 mm. Your cat gets to its tray; the dog does not.
Want it the other way, a door for a small dog between rooms? The Dogwalk® Small Dog Door Tunnel fits the same thickness range with a larger 180 × 227 mm opening.
Not sure what you have? Email a photo of the door’s edge with a tape measure across it to info@petnest.co.nz and we will tell you which model fits.
Quick answers
Which cat door fits an internal door?
Measure the door's thickness. Many internal doors are thicker than 30 mm, so the Catwalk Wood-Fitting Cat Door Tunnel (panels 11 to 52 mm) is usually the right model. The Slim Line version suits doors from 11 to 30 mm.
Can you put a cat door in a hollow-core door?
Yes. A hollow-core door is two thin skins over a light frame. The tunnel model lines the cut-out between the skins so the hole looks finished and the cavity is closed. Keep the cut-out inside the solid timber frame around the edge of the door.
How do I stop the dog using the internal cat door?
A standard cat opening (155 x 157 mm) is too small for most dogs. For a small dog that could squeeze through, the Catwalk Multi-Magnetic opens only for a cat wearing the collar magnet, so the litter tray and cat food stay cat-only.
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