Can You Install a Cat Flap in Double Glazed Glass? (Complete Guide)

If you’ve recently added a new furry friend to your family, then you’ll probably be in the process of planning a few home modifications. 

At the top of the list: installing a cat flap. 

However, if you already have double glazing installed and want to add a cat flap to the double glazing, then you’ll need to be aware: You cannot cut directly into an existing double glazed unit.

In this article, the Stevenage Glass team of expert glaziers have shared their insights. Keep reading to find out how you can successfully have a cat flap installed alongside a double glazing unit. 

Why can’t you cut a cat flap into double glazing? 

A cat flap cannot be installed by cutting directly into an existing double glazed unit. This would cause it to fail immediately.

This is because double glazing works by having two panes of glass permanently sealed together, with an insulating gap existing between them. 

So, if you attempt to cut into the glass after it has been installed, it would immediately break the sealed unit. This would cause the insulation to fail, and often cause the glass to either shatter or weaken significantly. 

Instead, there is an alternative process that can allow you to successfully add a cat flap. This involves replacing the glass unit with a new sealed pane, which is specifically manufactured to accommodate a cat flap. Let’s go into this in more detail. 

How does cat flap installation in double glazing work?

To correctly install a cat flap in a double glazing unit – without causing it to fail – you will need to enlist the assistance of a professional. 

The typical process of professional cat flap installation into glass involves: 

• Measuring the existing glass unit (including the specifications of the current unit, and the positioning requirements for the cat flap). 
• Manufacturing a new double glazed unit, which is made to order. This then features an aperture (for the cat flap), which is pre-cut during manufacturing.
  • Note, it is not possible for this hole to be added after this stage. 
• The glass is toughened and sealed, to create the double glazing unit. 
• The old glass is removed and replaced with the new double glazing unit. 
• Once the replacement double glazed panel is fitted (this can be done while keeping the pre-existing frame), the cat flap can be installed into the pre-cut opening.

Typically, the timescale for manufacturing a custom double glazed unit is around 1-2 weeks. 

What types of glass can be used?

The types of glass that are most commonly used for double glazing units are:

• Toughened safety glass – In the UK, this is typically required for doors and low-level windows
• Standard sealed units – Often used for installations positioned higher up in a property (where UK safety glazing regulations don’t apply)
• Units in various thicknesses – To match existing glazing units present in other areas of the property. This ensures consistent insulation performance throughout the property, and ensures the new pane correctly fits within the existing frame system. 

Where is the best place to position the cat flap?

For most average-sized cats, the standard recommended positioning is for the base of the flap to be set at ~150mm from the bottom of the frame. 

You will also need to ensure that the size of the flap is compatible with the size of your pet.

For example, larger cat breeds (such as Maine Coons or Ragdolls) may require larger apertures than standard cat flaps. 

Why professional installation matters

Installing a cat flap in a glass unit cannot be successfully achieved as a DIY installation.

Incorrect measurements or a DIY installation will result in an unusable or faulty unit, which needs to be completely replaced. 

Poor fitting can also compromise the unit’s security, and also mean your property fails to meet UK regulations for external doors and safety glazing.

By working with a professional installer, you can maintain optimum thermal performance and weatherproofing for your property, and achieve a dependable unit with a flawless finish. 

Although the process is more expensive than a simple door installation, a professional installation is the only way to properly maintain your double glazing’s energy efficiency. 

At Stevenage Glass, we are specialist glaziers with over 60 years’ experience manufacturing bespoke orders for the trade and public. 

So, if you’re interested in adding a cat flap to your existing double glazing unit, our team are on hand to help.