Bava Batra

in a large residence,  the latter is at liberty to use the projecting beams  and the cavities in the walls  up to a distance of four cubits [from his room], and also the thickness of the wall,  if this is the local custom, but not [the part of the wall facing] the front garden.  R. Nahman, however, speaking for himself said that he may use even the side facing the front garden, but not the yard at the back of the house. Raba, however, said that he may use the yard at the back also. Rabina said: [If a man is allowed by his neighbour to support] the beam of his hut [on his wall] for thirty days, this does not constitute prescriptive right,  but after thirty days it does constitute prescriptive right. If the hut, however, is for religious purposes,  [should no objection be raised] within seven days, this does not constitute prescriptive right, but [if objection is raised only] after seven days, it does.  If, however, he attaches it with clay [and still the neighbour does not object], he acquires prescriptive right immediately. Abaye said: If there are two houses on opposite sides of a public thoroughfare, the owner of the one should make a parapet for half his roof, and the other a parapet for half his roof, in such a way that the parapets do not face one another,  though each should extend [his parapet a little beyond the middle].  Why [does Abaye] state [this rule in connection with] a public thoroughfare, [seeing that] it could apply equally to private ground? It was more necessary to state it in connection with a public thoroughfare. For you might think that in this case one might [refuse to build], Saying to the other: When all is said and done you have to guard your privacy against the public;  therefore we are told here that this is not so, since the other can retort: The public can only see me by day but not by night, whereas you can see me both by day and night; or again, the public can see me when I am standing but not when I am sitting, but you can see me whether I am standing or sitting; the public can see me when they look directly at me, but not otherwise, but you see me even without looking. The Master has just said: 'The one should make a parapet for half his roof and the other should make a parapet for half his roof, In such a way that the parapets do not face one another, though each should extend [his parapet a little beyond the middle].' Surely this rule is obvious? — We require it for the case where one of the owners builds a parapet first [without consulting the other]. You might think that in that case the other is' entitled to say to him: Complete the parapet and I will reimburse you.  We, are therefore told [that he cannot insist upon this], since the other can say to him: Why don't you want to build? Because it might weaken your wall. I too [don't want] my wall to be weakened. R. Nahman said in the name of Samuel: If a man's roof adjoins another man's courtyard,  he must make a parapet four cubits high, but between one roof and another this is not necessary. To this R. Nahman added in his own name that a wall of four cubits is not required, but a partition of ten handbreadths is required. For what purpose [is such a partition required]? If to prevent 'overlooking' we require four cubits? If for the purpose of convicting his neighbour of felonious entry,  a mere fence of sticks would suffice? If to prevent kids and lambs from jumping over, a partition too high for them to jump over at a headlong run would suffice? — The actual reason is that he may be able to convict his neighbour of felonious entry. If there is only a fence of sticks, the latter can find an excuse,  but if there is a partition of ten handbreadths he can find no excuse. An objection was brought [against this ruling of R. Nahman] from the following: If the other's courtyard is higher than his roof, there is no need for it. Does not this mean that there is no need for a partition at all? — No; it means that there is no need for a wall of four cubits, but a partition of ten handbreadths is required. It has been stated: If two courtyards adjoin and one is higher than the other, R. Huna says that the owner of the lower one has to build [the party wall] up from his level, and the owner of the higher one starts building from his level.  'Ulla and R. Hisda, however, say that the owner of the higher one has to assist  the owner of the lower in building from his level. It has been taught in agreement with R. Hisda: If there are two adjoining courtyards of which one is higher than the other, the owner of the higher one must not say to the other, I will start building [the party wall] from my level, but he must assist the other to build from his level.  If, however, his courtyard is higher than his neighbour's roof, he has no liability. Two men were living [in the same house], one in the upper room and one in the lower. The lower, room began to sink into the ground, so the owner of the lower room said to the one above: 'Let us rebuild the house.' The other replied: 'l am quite comfortable.'