One should refrain from moving houses until the 15th of Av if it is possible for one to do so.
 Igros Kodesh 9/228 [brought in Shulchan Menachem 3 p. 48; Sha’arei Halacha Uminhag 2/225]; Not found in other Poskim.
 The reason: Seemingly the reason for this ruling is because one is to avoid doing things that change his Mazal during a period of time that a Jews Mazal is bad, just like one is to avoid judgment with a gentile during this time. Alternatively moving is included within matters of joy and one is to avoid doing matters of joy until the 15th of Av. The reason for why after the 15th of Av there is no need to refrain from moving, seemingly is because it follows the ruling of the Chasama Sofer 551 regarding avoiding judgment that it only extends until the 15th.
Not to move at all during Av: In another dated letter the Rebbe writes one is to avoid moving throughout the month of Av and is rather to try to move in Elul, the month of mercy. [Igros Kodesh 19/390]