Posted October 13, 2026
To replace an existing cat flap, check the size of the old opening, the condition of the frame and whether the new cat flap matches the existing cut-out. If you are upgrading to a microchip cat flap, the new model may need a different opening or adaptor. If the flap is in glass, ask Sharp Glass to check the panel before replacing it.
At Sharp Glass, we help Christchurch homeowners replace and install pet doors, including standard cat flaps, microchip cat flaps and customer-supplied pet doors.
Most people replace a cat flap because it has stopped doing its job.
It might still open and close, but if it lets in cold air, leaks in bad weather, no longer locks properly or does not suit your cat anymore, it may be time to upgrade.
Common signs it is time to replace your cat flap:
Replace like-for-like if the old flap worked well and the new model matches the existing opening. Upgrade if the old flap is draughty, insecure, too small, outdated or too basic for your home.
| Situation | Best replacement direction | Why |
|---|---|---|
| Old cat flap worked well but is broken | Like-for-like replacement | May suit the existing opening |
| Flap is draughty or leaking | Better-sealed replacement | May improve comfort |
| Other cats are entering the home | Microchip cat flap | Gives better access control |
| Cat has outgrown the old flap | Larger cat flap or pet door | Improves comfort and usability |
| Renovating the room or door | Upgrade option | Better chance to improve appearance and function |
If you are changing brands, changing size or moving from a standard flap to a microchip cat flap, do not assume the old opening will work. The new frame, tunnel depth, adaptor and cut-out size may be different.
If you are unsure about sizing, read our guide on how to choose the right pet door size.
If the new cat flap does not fit the old hole, do not force it into place. The opening may need adjusting, the door may need repair, or the panel may need replacing.
This often happens when changing brands, changing sizes or upgrading to a microchip cat flap.
A larger cat flap may need a bigger opening. A smaller cat flap may leave visible gaps around the old cut-out. If the frame does not sit flat, it can be harder to seal and may let in draughts or water.
In a timber door, the opening may be adjustable depending on the condition of the door. In glass, a mismatch can be more involved because the panel may need replacing.
A poor fit may look fine at first, but it can create movement, gaps, weak fixing points or weatherproofing issues later.
Yes, you can replace a cat flap in glass, but the right method depends on the glass type and the existing cut-out.
| Situation | What it usually means |
|---|---|
| Existing glass has a suitable cut-out and the new cat flap is the same size | Replacement may be straightforward. |
| New cat flap is a different size or the frame does not suit the old opening | The glass panel may need to be replaced. |
| Cat flap is in double-glazed or toughened safety glass | The glass usually cannot be cut after manufacture. |
| A new pet door is needed in toughened or double-glazed glass | A new glass panel or double-glazed unit is usually made with the correct cut-out. |
| You are unsure what type of glass you have | Ask a glazier to check before buying or fitting the replacement cat flap. |
That means if your current cat flap is in glass, the best first step is to check:
For more detail, read our guides on how to install a cat flap in your glass door and how to install a pet door in glass.
Sharp Glass offers free, no-obligation quotes for pet door installation in Christchurch. We can also install customer-supplied pet doors and flaps where the product and installation location are suitable.
Use Sharp Glass because replacing a cat flap is not just about the flap. The existing cut-out, panel type, replacement model, sealing and finished fit all need to work together.
As The Good Guys in Glass, we help Christchurch homeowners understand what is possible before the work begins. If the replacement is straightforward, we can let you know. If a new panel or different approach is needed, we can explain that clearly too.
We can help check:
If you already have a replacement cat flap, we can check whether it is suitable. If you have not bought one yet, we can help you understand what will work before you spend money on the wrong product.
Learn more about our pet door installation in Christchurch.
To cover an old cat flap, the best option depends on where it is installed. In a timber door, the opening may be patched or repaired. In glass, the cleaner option is usually to replace the glass panel, especially if you no longer want a flap there.
Yes, some doors or panels can be supplied with a cat flap already installed or prepared for one. If the cat flap needs to go into glass, double glazing or a sliding door, it is better to speak with a glazier first so the panel and opening are made correctly.
You can buy replacement cat flaps from pet stores, hardware stores, online retailers and pet door suppliers. Before buying, check the existing cut-out size, outside frame size and whether the new model needs an adaptor.
Most cat flaps are held in place with screws, clips or a removable frame, but the exact method depends on the brand and model. Check the manufacturer’s instructions before removing it. If the flap is fitted into glass, get advice before pulling the frame apart.
Alternatives to cat flaps include keeping your cat indoors, using a secure outdoor cat enclosure, supervised outdoor time, or setting up a regular door-opening routine. If the goal is controlled access, a microchip cat flap may be a better upgrade than removing the flap altogether.
Cat flaps can be a good idea if you want your cat to move in and out without needing someone to open the door. They work best when they are the right size, installed in the right location and sealed properly. If other cats are entering your home, a microchip cat flap may be a better option.
You can let a cat outside without a cat flap by opening the door manually, using a secure outdoor enclosure, creating supervised outdoor time or setting up a regular access routine. If convenience is the issue, replacing the old flap or upgrading to a microchip cat flap may be the better long-term option.
It can, depending on your insurer and where the cat flap is installed. Some policies may treat a cat flap as a change to home access or security. Check with your insurer before installing or replacing a cat flap, especially in an external door, glass door or sliding door.
Yes, most cat flaps need an opening in the door, glass panel or wall so your cat can pass through. If the flap is going into glass, double glazing or safety glass, the panel may need to be assessed or replaced rather than simply cut on site.
The cost to install a cat door in New Zealand depends on the cat flap type, installation location, glass or door material, and whether a replacement panel is needed. For Christchurch homes, Sharp Glass can provide a free, no-obligation quote based on the existing setup.
