Double glazing can be equipped with dog and cat flaps to let your pet go and go whenever they want. These are also great to keep an eye on your pet while you're away. You can put in a cat flap in an existing uPVC or double glazing sealed unit. https://catflapdoubleglazing41986.onzeblog.com/30805431/installing-a-cat-flap-in-a-upvc-door-cost