Yosef Karo

“ There are those who say that this does not need a form of a doorway. Rem"a: However, if the [added] wall is seven [tefachim] without counting the empty space, no form of a doorway is needed to the end of the [other] wall, given that seven is the minimum measurement for a [wall of a] sukkah. Obviously no form of a doorway is needed when the wall is full. The practice of making a form of a doorway when the walls are full is just for decorative reasons (R"an, Maggid ch.4, Kol Bo, Beit Yosef in the name of the Mordechai) . ”

“ According to the Ramba"m, even if there is a form of a doorway, if there is an opening greater than ten, it is invalid unless the non-open part is greater than the breaches. Rem"a: Our custom now is to make whole walls because not everyone is knowledgable about the laws of walls (Kol Bo) . And if one does not have enough material for walls, it is preferable to make three complete walls rather than four that are incomplete (Mahari"l) .
סעיף ה
כשהכשירו בשתי דפנות העשויות כמין ג"ם בטפח וצורת פתח אפי' אם יש בשתי הדפנות פתחים הרבה שאין בהם צורת פתח שכשתצרף כל הפרוץ יהיה מרובה על העומד כשרה. ”

“ If one leans the schach on the posts and the legs are walls, even if there are not ten [tefachim] from the bed to the schach, it is valid, because there are ten tefachim from the ground to the schach. ”