A Black Day for Mayberry - S4-E7
Character mistake: When Opie comes in at the beginning of the episode and asks where Andy is, the exchange ends with Barney asking "Something you want to see him about?" and Opie replying "No, I'll wait," which makes no sense in context. It would have made more sense if Barney had asked "Do you want to leave him a message?"
Answer: Those "boxes" are valences that used to be very common, before air conditioning. They allow for windows to be open during rain storms. They permit air circulation, without letting the rain in.