Responsa for Zevachim 125:2

Q. A father left a house and a yard to his many children, so that his children A, B, and C were each entitled to one-eighth of this property. His son, A, bought one-third of his brother B's part, and C bought another third. One-eighth of the property is large enough to form a "usable unit."^*According to R. Isaac b. Samuel, a “usable unit” is an area of four cubits by six cubits. The law requires that property held in partnership can be partitioned (against the will of one or more partners) only if every partner is able to receive a usable part. A demands that it be partitioned in such a manner that he, A, receive his own part and the part he bought, as one unit. This division would be in accord with the rabbinical ordinance that upon division of property held in partnership, a partner should receive his part as one unit. C, however, desiring to block the partition of the property, is determined to waive the rabbinical ordinance originally intended in his favor, and demands that the part he bought from his brother be given to him separately. This would make the partition impossible, since one twenty-fourth of the property is too small a part to be used separately.
Q. The house is situated near the public thoroughfare and its northern door opens into the thoroughfare; while the yard extends south of the house, away from the thoroughfare. Upon partitioning this house among the heirs, one heir would receive the more valuable front entrance, while the other would have to open up a door into the alley on the western side. Moreover, a square cubit of ground in the northern part of the yard, near the public thoroughfare, has double the value of a square cubit in the southern part of the yard, away from the thoroughfare. How, then, can this house be properly partitioned among the heirs?
Q. Is the thickness of a wall, which can not be reduced without weakening the entire building, to be considered as space when the house is partitioned among heirs?
Q. What is the length of a tefah, six of which make a cubit?
A. C can not refuse to abide by a rabbinical ordinance, even though it was made in his favor, when such refusal inconveniences the other heirs.
A. To answer this question one must know exactly the plan of the property. However, one must keep in mind the following rule: The advantages that some parts of said property have over other parts can be divided into two classes: a) positional advantages that can not be changed, i.e., some parts are near the street, others are away from it; b) artificial advantages caused by the presence of buildings, rooms, and doors in some parts, and their absence in others. Therefore, regarding the greater value of some parts of said property because of positional advantages, the size of each part should be, upon partitioning, inversely proportional to its value, thus equalizing the value of each part. As regard the greater value of some parts because of artificial advantages, the heir receiving the more valuable part should pay the difference, in money, to the heir receiving the less valuable part, for with the money he receives the latter may so improve his part so as to have all the advantages the former has in his part.
A. No, the thickness of the above wall is not to be considered as space.
A. A tefah is the size of four thumbs measured at the middle.
SOURCES: Cr. 208; Pr. 237, 238, 239; Tesh. Maim. to Kinyan, 14; Agudah B. B. 25. Cf. Terumat Hadeshen 336.