How to Install a Cat Flap in a Glass Door or Panel Safely

Thinking about giving your feline friend the freedom to come and go? Installing a cat flap into a glass door or panel can be a game-changer, but it does require a bit more planning than a standard door install. Here's a step-by-step guide to help you get it right.

Is It Possible to Install a Cat Flap in Glass?

Yes, but it needs to be done correctly. Most modern glass doors are double glazed or tempered, and cutting into these requires specialist tools and experience. For safety and compliance, we always recommend working with a professional glazier.

If you're starting from scratch or planning a window upgrade, you can order glass pre-cut with a circular opening for a cat flap — ideal for new installations.

What You'll Need:

• A cat flap designed for glass (usually circular and microchip-compatible)
• Pre-cut toughened glass or existing glass with hole
• Screwdriver or drill (depending on model)
• Safety gloves
• Silicone sealant

Step-by-Step Installation Guide

1. Check Your Cat Flap Compatibility

Make sure your cat flap is suitable for glass installation. Many microchip and magnetic models come with an adapter specifically for circular glass cut-outs.

2. Get the Glass Ready

If you're replacing the glass:

• Hire a glazier to cut or supply a new toughened or double-glazed unit with a pre-cut hole (commonly 212mm diameter).
• Install the new glass unit in the door frame.

If the hole already exists:

• Clean the edges and ensure the hole matches your flap's fitting specs.

3. Fit the Adapter Ring (if needed)

Many flaps require a circular adapter to ensure a snug, secure fit in the glass. Attach this ring following the manufacturer’s instructions.

4. Mount the Cat Flap

Place the flap into the hole from both sides. Most units will screw together through the glass. Follow the supplied instructions, ensuring it’s level and tight.

5. Seal the Edges

Use a clear silicone sealant around the edge to keep out drafts and water. This also helps secure the flap and reduce rattling.

6. Test the Flap

Make sure your cat can easily push through. If it’s a microchip flap, follow the pairing instructions and test with your cat nearby.

Tips & Things to Avoid

• Never cut into toughened or double-glazed glass yourself — it can shatter.
• Avoid cheap flaps not designed for glass – they may not seal properly.
• Always measure carefully and confirm compatibility before ordering a flap or replacement glass.

Final Thoughts

Installing a cat flap into glass is perfectly doable with the right parts and a bit of professional help. It’s a sleek, space-saving option that works well with modern patio doors and large windows. Want help choosing the right flap for glass? Visit our full range at catflaps.co.uk or drop us a message — we're happy to help!