Can you put a cat flap in a fire door?
Get a priceNot into a fire door as it stands, no.
A fire door is tested as a complete door, made the way the manufacturer built it. If you cut a hole in the leaf you change that. Most of the time the certificate no longer applies to the door you have.
A plastic flap is also a poor thing to put in the way of a fire. It melts.
If one is already there
Flaps turn up in flat front doors now and then. Somebody got a cat, and somebody with a jigsaw was feeling helpful.
A door with a flap cut into it is a failed door in our report. It needs replacing with a certified doorset. There is no good way to patch a hole of that size.
What people do instead
Put the flap in a door that is not a fire door. A back door out of a kitchen, say, if the kitchen has its own fire door to the hall.
Or fit it in a wall panel or glazing unit beside the door, not in the door.
If you are buying a new doorset and want a flap in it, ask the manufacturer whether any flap is covered by the door's certificate. If they say no, the answer is no.
Letterboxes
The same applies to letterboxes. A fire-rated one that fits the door's certificate is a different thing from the metal one off the shelf. We look at them on every flat front door.
Send the postcode and a rough number. A price comes back the same day.
Get a price