If your windows were designed to be opened you should be able to do so . Your landlord cannot tell you to keep windows that were designed to be opened , closed all the time . Now If those windows were also designed to have screens and they dont send your landlord a letter (keep copy for self )that you want the window screens that belong to those windows put in in the next few days . Sending the letter out where you get a confirmation of delivery . See its sort of like having a deadbolt on a door and being told no you cant use it . Wich is nonsense . If your landlord refuses to honor the request call your city county govt center and ask for a housing inspector to speak with . If they come out and find no reason for you not to open windows and that there are missing screens they will order him to make repairs . Ask them about getting a copy of the report from any visit they make to your unit .