Fitting a Cat Flap - How to Fit a Cat Flap into a uPVC or Timber Door

Summary: How to fit a cat flap in wooden or PVCu doors. In this project we will show you all you need to know for fitting a cat flap into either a timber door or even a uPVC door. Learn how to measure your cat so that the flap is the correct height on the door, how to mark out the shape of your chosen cat flap on the door, how to use a jigsaw to cut out the area in the door for your cat flap and then how to fix it all together and then ensure that your door remains waterproof and resistant to any wind and rain outside.

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Fitting a cat flap can seem like a huge job to a novice DIY'er, especially through a uPVC door but if you simply stick to the instructions which always accompany the access cat or dog flap, its really quite a simple operation.

Measuring for a cat flap

Measuring for a cat flap

Tools Needed for Fitting a Cat Flap

To fit your cat flap correctly you will need the following tools:

  • Cordless drill/driver
  • Drill bits - one 5/6mm wood bit and one 10/12mm flat bit
  • Jigsaw with suitable blade for material you are cutting
  • Ruler
  • Pencil
  • Tape measure
  • Cat flap kit including fitting instructions (for the shape template)
  • Spirit level
  • Screwdriver
  • Spanner for tightening fitting nuts
  • Sandpaper
  • File and/or rasp
  • Silicone sealant and applicator gun
  • Paint and brush (for painting internal cut section of door if timber)

How to Fit a Cat Flap

Measure how Heigh Your Cat Flap Needs to be

Firstly measure your cat against the door to see how high the cat flap should be from the floor so that it can easily get out. Measure the distance from the floor to the underside of the cats tummy. Transfer this measurement onto the door which is going have the cat flap fitted, and, using a small spirit level mark a horizontal line, in light pencil across the door.

Mark the Centre of the Door

To find the centre of the door your should measure the width of the door and divide by two. Mark an "x" on this point on the door as this will be where the centre of the cat flap is. Always remember to measure twice and cut once!

Mark the Cat Flap Outline on the Door

Next, using the template in the instructions, mark the appropriate sized circle or square (depending on the shape of your cat flap) on the door using your ″X″ as the centre of the circle or square.

Centre point of cat flap

Centre point of cat flap

Cutting circle

Cutting circle

What if I Have no Instructions?

If for any reason you do not have the instructions you will need to dismantle the cat flap and mark out the opening on paper in order to measure the required hole diameter.

Ensure that you draw your shape, be it a circle or square, accurately on your piece of paper. If it's a square ensure that your shape is actually square (you can do this by measuring the diagonals between corners, they should be the same) and if a circle, it is actually a circle and not slightly ellipse.

Drill Holes for Your Jigsaw Blade

Drill a hole slightly larger than the width of your jig–saw blade so that the edge of the drilled hole is right on edge of the line of your shape on the door. The ideal drill bit to use here is a flat bit around 10mm.

If your shape is square, drill a hole just inside each corner and if your shape is a circle you may be able to get away with drilling one hole at the top. If not, divide the circle into sections by drilling holes top, bottom, left and right.

Cutting out Your cat flap Shape

With your holes in place you can now start cutting out your shape. In an ideal situation you would remove the door and place it on a flat, level surface to do your cutting but sometimes this is not possible so we will assume that the door cannot be removed and you will have to cut it in situ.

Push the jigsaw blade through one of the holes you previously drilled and ensure the base plate is flat and level on the face of the door and begin to cut, following your line and closely as you possibly can.

If you have a paneled door, as shown in the images below do not cut through the door mullions or vertical rails. Place the cat flap in the centre of one of the panels.

Do not attempt to push the jig–saw to make it cut faster. Let the blade and the motor do the work and you can then just guide the blade around to get a perfect circle or smooth–sided square.

A word of warning here: Some cats like to nudge themselves up against the door to let their owners know they are waiting to come in. Check the other side of the door before you start to drill and cut!!

Hole in Door

Hole in Door

Tidying up the Hole

When you have cut the hole, use a piece of sand–paper to smooth off the edge of the cut. Don't forget all of these instructions apply to uPVC doors as well as timber doors!

If you are indeed cutting a uPVC door, make sure that you are using the correct blade in your jigsaw. If in doubt, ask for advice on blades at your local DIY store.

Check the Flap Swings Smoothly

With the hole cut out, place the flap section up against the door and push the flap open to make sure it's a smooth action and it does not bind on anything. If it does, make note of where it is binding and use a file or rasp to adjust the size of the hole as required.

What Section Goes Where?

There are many different kinds of cat flap but all are fairly self explanatory from a fitting point of view as, usually, there is only one way they can go together.

The section with the flap should always go on the outside of the door as this will provide the best protection from the elements as you don't want the insides of the door to be exposed to, too much wind and rain as this will rot the door if it is timber. The manufacturers instructions should state this.

Drill Fixing Holes

Place the flapped section up against your door so that it sits exactly where you would like it to go and use your pencil to mark each fixing hole. Remove the flap and then drill your holes.

It's also a good idea to use a little sealant to make the external joints between door and cat flap water–tight and if the joint between the door panel and mullion has been stretched at all by the jig–saw vibration, it may be as well to make good with some decorators caulk.

If your door is timber, it is also a good idea to paint what will now probably be the bare sections of timber inside your cut out. This will help prevent any water and moisture soaking into the wood and causing rot.

Fix it all Together

Place the outer section on the door and push each fixing bolt through each hole and through the holes in the door. Push the inner section of the flap over the fixing bolts and screw a nut onto each one and tighten up.

Give it one final test by pushing the flap and if all is good you're done!

Cat flap fitted

Cat flap fitted

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