גגין וחצירו' וקרפיפו' כולן רשות א' הם לכלים ששבתו בתוכה שמותר לטלטלם מזה לזה אפי' הם של בעלים הרב' ולא עירבו יחד מותר לטלטל מחצר לחצר אחר' או לגג או לראש כותל שביניהם ומגג לגג אחר הסמוך לו אפי' גבוה ממנו הרבה ומהגג לקרפף שאינו יותר מסאתים או שהוקף לדירה אפי' הוא יותר מסאתים או למבוי שמתוקן בלחי או קורה אפי' לא עירבו בו ואע"פ שעירבו בני חצר לעצמן דשכיחי מאני דבתים בחצר מותר לטלטל כלים ששבתו בחצר זו לחצר אחר' ולא חיישינן שמא יטלטל גם כלים ששבתו בבית לחצר אחרת או לגג וקרפף:

Roofs, courtyards, and enclosed yards are all considered one domain with respect to utensils that were in them when Shabbat began. It is therefore permitted to carry such items from one to another—even if they belong to different owners who did not join in an eruv. One may carry from one courtyard to another, to a roof, to the top of a wall between them, and from one roof to another adjacent roof—even if the other is much higher. One may also carry from a roof to a karpaf not larger than two se’ah, or one that was enclosed for dwelling even if larger, or to an alleyway (mavoy) that has been properly prepared with a side-post (lechi) or beam (korah), even if no eruv was made there. Even though the residents of a courtyard made an eruv among themselves—since household items are commonly found in the courtyard—it is nevertheless permitted to carry utensils that were in this courtyard at the onset of Shabbat to another courtyard, and we are not concerned lest one carry items that were in the house to another courtyard, roof, or karpaf.

A karpaf larger than two se’ah that was not enclosed for dwelling has the status of a karmelit, and it is forbidden to carry from it to another karpaf—bringing in or taking out—except for four cubits total (two cubits in each).

Two courtyards that wish to make a joint eruv to permit even items that were in houses do not need a new eruv. Rather, the eruv they already made may be taken by one resident on behalf of all and placed in one of the houses of the second courtyard. If he wishes, he may even bring his own bread there, and then all are permitted. smalRema: This applies provided the residents of his courtyard first joined with him (Responsa of the Rosh §16), or they are not required to make an eruv as explained in Siman 370 (Beit Yosef). And provided the residents of the second courtyard made their own eruv; they do not need additional bread, as their existing eruv suffices.

Two courtyards cannot join in one eruv unless there is a doorway between them, or a window measuring four by four handbreadths, with part of it within ten handbreadths of the ground. If so, they may choose to make one joint eruv or each separately (see below Siman 386:2 regarding Israelites dwelling in two or three places).

A window between two houses, even if above ten handbreadths, if they wish, they may join together in an eruv. The same applies to a skylight between a house and an upper story—even above ten handbreadths—they may join, even if there is no ladder. /smallrema:

A house situated between two courtyards and open to both, and it joined in an eruv with both—but the courtyards did not join with each other—one may not carry items that were in houses from one courtyard to the other via that house. If there is a wall between two courtyards ten handbreadths high, or if the ground of one courtyard is five handbreadths higher and a five-handbreadth partition was built to complete ten, they cannot join in one eruv. If the wall is ten high for both and produce is on top, the residents of both courtyards may lower it into their courtyards and raise produce that was in the courtyards onto it, and lower it into the other courtyard—whether the wall is four handbreadths wide or not. But produce that was in a house: if the wall is four wide, it is forbidden to raise or lower it; if not four wide, it is permitted (provided they do not exchange items, as above Siman 346:1). If the wall is ten high for one courtyard but not the other (e.g., one ground is higher), the one for whom it is not ten high may use it even with house-items; the other may not use it even with courtyard-items—provided the wall is four wide. If not four wide, both may use it even for house-items, even if each made its own eruv.

If the wall was breached up to ten cubits, it is considered like a doorway—provided it was not completely breached. If breached more than ten cubits, it is considered like one courtyard and they must join in one eruv (certainly if there is no ten-high partition at all, they must join) (R. Yonatan Perek Chalon).

If a wall between two courtyards is ten high for both, and a ladder four wide was placed against it, and similarly in the second courtyard—even if the ladders are not directly opposite—if less than three handbreadths apart they are considered like a doorway. If three apart: if the wall is four wide, still considered a doorway; if not, not. This applies to a ladder with four rungs; fewer do not suffice unless its sides and rungs are heavy so its weight fixes it in place. If the wall is only ten high and one erects a ladder seven and a bit high, four wide, adjacent to the wall, it permits use of the wall and joint eruv, since less than three remain to the top. If one removed a section from the top to reduce it below ten: if four wide, effective for doorway and use; if not, ineffective except opposite that place.

If one built a platform at the base of the wall to reduce its height: if four long along the wall and four projecting outward, it permits use of the entire wall but does not count as a doorway unless it reaches the top. If not four by four, it does not help even opposite it.

If one inverted a vessel four by four and any height to reduce the wall below ten, it permits use opposite the reduction—provided it is affixed with mortar.

If one built platform upon platform: if the lower is four by four, or even if not but the upper is four by four and within three handbreadths, it permits use but not joint eruv.

A projection from the wall four by four with any ladder placed on it permits use—provided the lowest rung is within three of the ground and no gap of three between rungs, and the ladder rests atop the projection. If leaned beside it, no. If the wall is under twenty high, one projection in the middle suffices; if twenty high, two are needed—one within the lower ten and one within the upper ten—unless directly opposite each other enabling a ladder.

Two ladders placed side by side without four width, separated to total four, and the space filled with straw—this does not help, since one steps in the middle and cannot climb straw. If the ladder is central and straw on the side, it helps both for use and joint eruv.

If a ladder is not four wide and one carved the wall beside it to complete four, it suffices to carve ten high. If no ladder but one carved rungs into the wall, one must carve the entire height; this helps for both use and joint eruv.

If there is a tree beside the wall used as a ladder, they may join. But if an Asherah tree was used, they may not join, since it is forbidden to climb (as it is prohibited for benefit). The Rosh writes the opposite: a regular tree does not help, but an Asherah does if dry.

A trench between two courtyards ten deep and four wide—they cannot join even if filled with straw unless annulled. If filled with dirt or pebbles—even without explicit annulment—they must join (see Siman 358:2). Rema: Some say that if filled with produce, it is presumed annulled, as people commonly store produce there (Hagahot Ashiri).

If a plank like a bridge is placed from one edge of the trench to the other and is four wide, it is like a doorway—they may join or separate. Rema: The same if filled four wide with something permanently annulled (Beit Yosef). If the plank runs lengthwise four cubits, even minimal width suffices, since it reduced the width from four.

If the trench is ten deep for one but not the other, or equal for both, its law is like that of a wall.

A stack of straw between two courtyards: if ten high, each makes its own eruv. If reduced below ten during the week, they must join. While still ten high, neither may remove straw on Shabbat for his animal—even to place the animal there to eat. But if he can stand before it to prevent it turning elsewhere, that is permitted. According to the Rosh, even during the week one may not remove straw or position the animal by hand. This applies to a stack between courtyards; between two houses, one may feed his animal from it by hand.