Double glazing can be fitted with flaps for dogs and cats to let your pet leave and come as they please. They are also great to keep an eye on your pet while you're away. You can install a cat flap in an existing uPVC or double glazing sealed unit. https://catflapinstaller45995.targetblogs.com/31316022/installing-a-cat-flap-in-a-upvc-door-cost