Spencer...Trev can go through just fine but there is not a half inch to spare (or should I be talking metric ). Sometimes he will stand at the basement door and meow if there are people close by so that we will open it for him. Otherwise through the flap he goes! Our last standard poodle, Whitney, was a riot. You could be standing in the basement and look up the steps and there would be her head and neck sticking through the flap, looking very much like a mounted deer head!