How to fit a cat flap

Video by Paddy's DIY. This walk-through draws on the video "[36] Fitting a Cat Flap in a uPVC Door" from Paddy's DIY, a UK channel run by someone who trained as a locksmith after years in window and door fitting. The detail on removing the panel bead without cracking it is genuinely useful — worth a watch before you pick up a jigsaw.

1. Choose the right cat flap for your door

Not all cat flaps suit all doors. For a uPVC door with a double-glazed glass panel, you will usually be fitting the flap into the lower panel itself — not the door frame. Check whether the panel is glass or a solid uPVC insert. The approach is different for each, and some glazed panels cannot be cut without replacement.

For a solid uPVC or timber door, fitting is more straightforward. Match the flap size to your cat — a large breed needs a 4-way locking flap with a bigger opening, not the standard small size.

2. Mark the cutting position carefully

The flap should sit between 15 cm and 20 cm from the ground, measured to the bottom of the opening — high enough to keep out draughts, low enough for an elderly cat. Check that there is clearance on the outside too: a step, mat, or raised threshold can block the flap from swinging freely.

Use the cat flap's template or the inner frame itself to mark the cut lines. Double-check the position from both sides of the door before you reach for any tools. Once cut, you cannot undo it.

3. Remove the panel bead cleanly

On a uPVC door, the glass or solid panel is held in place by a plastic bead clipped around the inside edge. Use a wide flat tool — a uPVC bead tool or a stiff putty knife — to lever it off in sections without cracking it. Work from a corner, apply steady outward pressure, and it will pop free.

Keep the sections in order so you can refit them later. They are not always available as replacements, and a missing piece leaves a cold, draughty gap. That said, if the bead is old and brittle, now is a sensible time to order a replacement length before you start.

4. Cut the opening

For a solid uPVC panel: drill a pilot hole at each corner of the marked rectangle, then use a jigsaw with a fine blade to cut between them. Keep the blade speed moderate and let the tool do the work — forcing it chips the edges. A little masking tape over the cut line helps keep the surface clean.

For a timber door, the same approach works well. For glass panels, stop here and get a glazier involved — cutting toughened glass is not a DIY job.

5. Fit the cat flap frame

Separate the cat flap into its inner and outer sections. Feed the outer section through the hole from outside, then clip or screw the inner section against it from inside. Most flaps use through-bolts that sandwich the door panel between the two frames.

Check the flap swings freely and that the magnetic closure seats properly. Tighten the bolts evenly so the frame sits flush on both sides. An uneven fit leads to gaps, rattling in wind, and a cat that will not use it.

6. Refit the panel bead and seal the edges

Clip the panel bead back into position around the cut-out. The fit should be snug against the new frame. If the bead no longer reaches because of the cut, trim it carefully with a mitre saw or fine-tooth hacksaw.

Run a thin bead of clear silicone around the outside edge of the cat flap frame where it meets the door panel. This stops water tracking behind the frame. Smooth it with a dampened finger and wipe away any excess before it sets. Let it cure fully before your cat discovers the new feature.

When to call a handyman

Call Richard if the door has a toughened glass panel that needs a glazier, if the bead has snapped or is missing, or if the door is composite and the inner structure makes cutting tricky. Fitting a cat flap into a brick or rendered wall — with a tunnel section — is also a more involved job where a pair of hands and the right drill bits make a big difference.