Starting in the southeast corner of the Azarah were three chambers which took up the entire 11-amah length of the Ezras Yisrael and continued into the Ezras Kohanim.
The first of these was the Chamber of Melach which held a large supply of salt used fordifferent purposes, such as tanning hides in the adjacent Chamber of Parvah and applying to the sacrificial parts before they were placed upon the Mizbeyach.
On the roof of this chamber was a terrace where the Kohanim could eat sacrificial meat. Although, as a general rule, all rooftops and second stories in the Beis Hamikdash were not imbued with the sanctity of the Azarah and thus one would not be allowed to eat sacrificial meat there, this does not hold true when the only access to that area is through the Azarah. Since the stairs of this terrace led down into the Chamber of Melach which, in turn, opened to the Azarah, this granted the roof a level of sanctity equivalent to that of the Azarah.
The same principle is applied to the mikveh located on the roof of the adjacent Chamber of Parvah that was used by the Kohen Gadol on Yom Kippur. His immersions there needed to be carried out within the confines of the Azarah, and since the only way to access the mikveh was through the Azarah, it was granted kedushas Azarah even though it was located on a roof.
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