I am a renter and live on the second floor of a 100 year old house. The windows are EXTREMELY out of square and my screen inserts leave a 1/4 to 1/2 inch gap for mosquitoes to get through. I don't know how they find that gap, but they do. I can't sleep without a mosquito net if I have the windows open/screen in. I have been trying to think of ways to cover that gap when the screens are in - I live in Seattle though, so it has to be something that can be removed and redone easily as the temperature varies wildly.