Yes, adding a cat door to an existing timber door is a job most handy homeowners can tackle themselves. As long as your door is solid timber or a solid-core timber door (not a hollow-core door with thin skins), and you're comfortable using a jigsaw and drill, this is a satisfying weekend project. If your door is hollow-core, glazed, or a fire door, read on — there are important exceptions.
Check Your Door Type First
Before you buy anything, identify what kind of door you have:
- Solid timber doors – ideal for cutting a cat flap opening. These are common in older NZ homes.
- Solid-core doors – have a solid internal core (often MDF or particleboard) with timber veneer skins. These can also be cut, but take care with the veneer edges.
- Hollow-core doors – have a cardboard or foam honeycomb core with thin plywood or hardboard skins. These are not suitable for cat doors; the opening will have no material to support the flap frame and the door will be structurally weakened.
- Fire doors – must never be modified. Cutting into a fire door voids its fire rating and may breach the NZ Building Code. Check with your local council if you're unsure.
- Glazed or louvre doors – modifying these involves glass work and is best left to a professional joiner.
If your door is a rental property door, check with your landlord first. Under Tenancy Services Healthy Homes rules, tenants generally cannot make structural alterations without written consent.
Tools and Materials You'll Need
- Cat door/flap kit (sized for your cat — measure your cat's height and width at the shoulders)
- Tape measure and pencil
- Combination square
- Power drill with a spade or hole-saw bit
- Jigsaw with a fine-tooth timber blade
- Sandpaper (80 and 120 grit)
- Chisel (optional, for tidying corners)
- Screwdriver or drill driver
- Exterior-grade sealant or paint to finish cut edges
Cat door kits are widely available at Bunnings and Mitre 10. Choose a kit rated for exterior use if the door leads outside, as these have better weather seals.
Step-by-Step Installation Guide
1. Choose the Right Position
Position the cat door so the bottom of the flap opening sits roughly 75–100 mm above the bottom rail of the door. This gives your cat a comfortable step-through height while keeping the door structurally sound. Avoid cutting too close to the door edges, hinges, or lock hardware — stay at least 100 mm from any edge.
Centre the flap horizontally on the door unless there's a reason to offset it (e.g., a door frame obstruction on one side).
2. Mark the Cut-Out
Use the template provided in your cat door kit (most include one). Tape it to the door at the correct height, check it's level with a combination square, and trace around it with a pencil.
3. Drill Entry Holes
Drill a hole at each corner of your marked rectangle using a spade bit or hole saw. These holes give your jigsaw blade a starting point and create neat internal corners.
4. Cut the Opening
Insert your jigsaw blade into one of the drilled holes and cut along the pencil lines, working from corner to corner. Cut slowly and steadily — let the blade do the work. Keep the jigsaw base plate flat against the door face.
Safety note: Wear safety glasses and hearing protection. Secure the door so it can't move while you're cutting — clamp it to a workbench or have a helper hold it steady.
5. Smooth and Seal the Edges
Sand all cut edges smooth, starting with 80 grit and finishing with 120 grit. This is an important step: bare timber edges on an exterior door will absorb moisture and swell or rot if left unsealed. Apply a coat of exterior primer or paint (brands like Resene or Dulux offer suitable exterior primers) to all cut surfaces. Allow to dry fully before fitting the flap.
6. Fit the Cat Door Frame
Most cat door kits come in two halves — an inner frame and an outer frame — that sandwich the door. Feed the flap assembly through the opening, align both frame halves, and secure with the screws provided. Don't overtighten; snug is enough to compress the weather seal without cracking the frame.
7. Test and Adjust
Open and close the flap several times to check it swings freely and the magnetic or brush seal closes properly. If the door has a locking slide, test that too.
Painting and Finishing
If your door is painted, touch up around the new frame with a matching exterior paint. Wattyl and Resene both offer colour-matching services if you need to blend in with an existing colour.
When to Call a Professional
Call a qualified joiner if:
- You're not confident using power tools
- Your door is hollow-core and needs replacing with a solid-core door to accommodate a cat flap
- The door is a fire door (modification is not permitted)
- The door is glazed or has decorative mouldings that complicate the cut
- You want a larger dog door installed — larger openings can affect door integrity and may benefit from professional assessment
A skilled joiner can also supply and hang a replacement door if your current one isn't suitable. You can find qualified local joiners on tradedirectory.co.nz.
Note: This type of work is not electrical, plumbing, or gas work, so there are no licensing restrictions for homeowners doing it themselves. However, always work safely and follow the manufacturer's instructions.
