Yosef Karo

“ Paragraph 1 - A porch is the way to get to the upper chambers that are open to it. It is in the yard and one climbs up to it with a ladder. The residents of the upper chambers descend to the yard from it and pass to the public domain. ”

“ They do not render the other residents of the yard forbidden [from carrying if they do not make an eruv] , as a ladder is considered an opening, and it is considered to be two yards with an opening between them such that if they want to, they can make one eruv, and if they want they can make individual eruvim as long as the residents of the porch make an eruv for themselves so that they will be permitted to carry within their own domain [and thus will not render others forbidden if they pass through their domain, see chapter 378] . ”

“ Therefore, both are forbidden from removing household objects to there until they make an eruv.
סעיף ב - אם לא ערבו יחד ויש בחצר תל או עמוד שהוא משתף בין שניהם, אם אינם גבוהים עשרה טפחים, הרי אלו נחשבים בין החצר ובין המרפסת ושניהם אסורים להוציא שם כלים שבבתים. ואם הם גבוהים מקרקעית החצר עשרה טפחים (ובתוך עשרה למרפסת) (טור) והם בתוך ארבעה טפחים למרפסת, בני מרפסת מתרים לפי שתשמישו (להם) בנחת מלבני החצר. ”