Diy Windows In Garage Door . After the paint is dry, clean the glass with windex and then use rubbing alcohol to remove any dirt and debris from the glass. Therefore, the opening you’ll cut out of the panel has to be big enough for the back of the window to fit. DIY Frosted Garage Door Windows Mother Daughter Projects from www.motherdaughterprojects.com Using a flathead screwdriver or another flat tool pry the window trim off the window. If you want to add windows to an existing garage door, you may be in luck. In the pictures, the thermal windows will be installed on the third panel of the door, so it needs to be removed.