משנה אויף במדבר 24:2

One may not make a window to open into a jointly held courtyard. If he bought a house in another [and adjoining] courtyard he may not open it into a jointly held courtyard. If he built an upper room over his house he may not make it open into the jointly held courtyard; But, if he wishes, he may build another room within his house or build an upper room over his house and make it open into his own house. In a jointly held courtyard a man may not build a door directly opposite another’s door, or a window directly opposite another’s window. If the window was small he may not make it larger; if it was a single window he may not make it into two. But in the public domain he may open a door opposite another’s door, or a window opposite another’s window. If the window was small he may make it larger; if it was a single window he may make it into two.