Placing sefarim on top of each other:
It is permitted to place a Chumash on top of Nevim or Kesuvim. However one may not place a Nevim or Kesuvim on top of a Chumash, and one may not place a Chumash on top of a Sefer Torah. One may place a Kesuvim over a Navi. It is permitted to bind a set of Tanach in one binding in any order that one chooses. [There is no order regarding Sefarim of Torah Shebaal Peh such as Gemara, Mishneh and their commentaries, and they may thus be placed on top of each other. Some however are stringent in this regard. However they may not be placed on top of a Chumash, Nevim or Kesuvim. The custom is to treat a Siddur with the same status as Nevim and Kesuvim. The Chabad custom is to treat a Tanya with the same respect as a Chumash and hence we do not place other Sefarim over it, including a Chumash. One may not however place a Tanya on top of a Chumash.]
 282/19; See Hiskashrus 709; Ginzei Hakodesh 3
 Michaber ibid
 Rama ibid
 Rama ibid; Ran Megillah 8b; Tosafus Baba Basra 13b “Rebbe Yehuda”
 Based on Rama ibid regarding Nevim and Kesuvim and the fact that there is no such law mentioned regarding the Sefarim of the oral Torah. So is also understood from M”A 25/4. See Ginzeiy Kodesh 3/29
 Leket Yosher Yoreh Deah p. 59 that his teacher, the Terumos Hadeshen would not place the Sefarim on top of each other; It is told that the Rebbe once removed a Sicha from on top of a Shulchan Aruch. [Yoman 28th Sivan 1967]; See Ginzei Kodesh ibid
 Riy Migash 92
 See Hiskashrus ibid; Ginzei Hakodesh ibid
The reason: This is due to the great amount of verses from Tanach quoted there.
 See letter of Rebbe Rayatz brought in Kitzurim Veharos on Tanya p. 118; Maaseh Melech p. 7
 Pashut. And so is told that the Rebbe at times went out of his way to remove a Tanya from on top of a Chumash.