This Halacha is an excerpt from our Sefer
It is forbidden to have marital relations on Tisha B’av.
Must one keep Harchakos during Tisha B’av? Some Poskim rule one is not to sleep in the same bed as his wife on the night of Tisha B’av. This is the proper custom, as a guard against coming to have marital relations. Likewise, one may not touch his wife [affectionately] during this time. However, during the day, one may be lenient [regarding touch]. [It goes without saying that the other Harchakos do not have to be kept on Tisha B’av even at night. However, some Poskim rule that it is proper to follow all the Harchakos restrictions at night. Furthermore, some write it is proper to be stringent even during the day, just like the law on Yom Kippur.]
Night: On the night of Tisha B’av one is not to touch his wife affectionately or sleep with her in the same bed. Some rule one is to also follow the other Harchakos restrictions at night.
Day: By the day of Tisha B’av one may be lenient regarding touch, although some rule that one is to be stringent just like by night, even regarding the Harchakos restrictions.
 Michaber 554:1; Taanis 30
 Michaber 554:18; Admur 40:8
 Hagahos Mordechai on Moed Katan
 Michaber ibid; Admur ibid
Stringency or letter of the law: This is stringency, however from the letter of the law is allowed. [Admur 40:8] However by Yom Kippur it is forbidden from the letter of the law. [Admur 615:1]
 M”A 554:19 in name of Darkei Moshe; M”B 554:37
 M”A ibid; M”B ibid; Chayeh Adam 135:12; Ben Ish Chaiy Devarim 23
The reason: As on Tisha B’av the women do not wear nice clothing and hence there is less worry that something will occur. [Shaar HaTziyon 554:44] Some Poskim rule that if one’s wife wears nice clothing one is to be stringent even during the day just like the law on Yom Kippur. [Shaar HaTziyon 554:44 based on Machatzis Hashekel 554:]
Opinion of Admur: See Admur Kuntrus Acharon 40:2 that “One should not differentiate between day and night as regarding Tisha B’av the Poskim did not differentiate in this”. However, perhaps this is only in reference to sleeping in the same bed and not with regards to touch.
 Ben Ish Chaiy Devarim 23 brought in Kaf Hachaim 554:85; Piskeiy Teshuvos 554:17
 Hiskashrus based on Admur 184:6 Kuntrus Acharon 2 “Due to this it is not similar to Yom Kippur and Tisha B’av” thus implying that Yom Kippur and Tisha B’av are both forbidden in Chibuk and Nishuk throughout the time; Piskeiy Teshuvos 554:17 in name of Az Nidbaru 8:61; See Shaar HaTziyon 554:44 based on Machatzis Hashekel 554:19