https://elearnportal.science/w....iki/Fitting_a_Cat_Fl
Cat and dog flaps installed in double glazing allow your pets to come and go whenever they like. They are also great for keeping an eye on your pet while you are away from home. It is possible to install a cat flap into an existing uPVC panel or double glazing glass sealed unit, however you'll need to replace the piece with a premade hole. A glazier is able to do this with the right equipment and the right training. Easy to install A cat flap is an excellent option to allow your pet access to the outside without you having to constan