General Information About Pet Doors
"Through the Glass"

The major thing to realize regarding an "In-The-Glass" pet door is that you cannot cut tempered glass!! If you attempt to cut tempered glass, it will shatter!

How do you tell if your glass is tempered?  Tempered glass usually has an indicia, or 'bug' as it is called in the trade, in one corner. If you see a bug, the glass is tempered. If you don't see a bug, well.... it may be plate, which you can cut, and it may not.  Older houses are more likely to have plate glass; newer houses probably have tempered. Dual-pane, insulated glass units are almost certainly tempered and shouldn't be cut into anyway. Countries outside the USA would appear to have more plate glass.

Plate glass can be easily cut with a glass cutter. Problem is, it isn't very strong. Some pet doors are specially designed to spread the force over a wide area (see below) but they're only meant for cats or for small (and non-hyper) dogs.

The best approach is to have a professional glazier from a local glass shop get you a new piece of glass with the circular cut-out required done for you. This can work for dual-pane glass as well as single pane.

Another way to put a pet door "in the glass" is to replace the glass with 'Lexan'--the generic name is polycarbonate--which looks like glass but which can be drilled and sawed like wood. Use a minimum thickness of  ³/₁₆" if possible. Also, look for 'scratch resistant' Lexan.

Once the Lexan or new glass is installed, you can install most pet doors in it. Just be sure the pet door is appropriate for thin cross section installations.

Hot Tip:  In addition to glass, these cat flaps are fine candidates for any thin material including plywood or screen.

A Cat Flap Installed Directly
"Through the Glass"