A ledge that juts out above ten tefachim over a Reshus Horabbim is a Makom P’tur. If it is a windowsill, it is deemed Choray Reshus Hayochid. In either case you may put things on and off of it from inside the house. (ShA 2 – MB 8)
The objects that are allowed to be put on the windowsill are only breakable ones – which if they fall and break in Reshus Horabbim you won’t be tempted to carry them back in. However, if the ledge is 10 tefachim above a Karmelis, even sturdy objects may be placed on the windowsill. (ShA 3)
There is no concern for objects falling off a wide, elevated porch. If you are able to hold the object while standing on the porch, you may bring it in and out of the porch. (Rama 3)
