The laws regarding a married woman covering her hair while in the privacy of her house, in front of her husband, and during intimacy:
When she is alone at home: From the letter of the law, a married woman is not required to cover her hair in the privacy of her home when no one else is around. If her husband is not around, she may do so even when she is a Nidda. Nonetheless, the Talmud and Poskim encourage a woman to cover her hair at all times, even in the privacy of her home, and doing so merits one to have children fit to be Kohanim Gedolim. Furthermore, according to the Zohar, it is a complete prohibition to reveal even a single hair of the head even in one’s home, and one who is not careful in this causes their home to be stricken with poverty, the side of evil, and causes spiritual challenges for their children, as well as other Tzaros, while one who is careful in this merits to have illustrious children, and have her husband be blessed with all blessings of above and below, with wealth and grandchildren. This Zoharic statement is recorded in the Poskim and they conclude that it is proper to be followed. The Rebbe on many occasions encouraged women to follow this act of piety and benefit from its positive effect on one’s children, and so is the custom of all G-d fearing women today to not uncover their hair even in the privacy of their own home. Some Poskim rule that according to the Zohar who prohibits to reveal any hair of the head, the sideburn areas and neck areas of her hair is also included, and it is not to be revealed even in the privacy of one’s home.
When she is alone with her husband but is a Nidda: When the wife is a Nida, it is forbidden from the letter of the law for her husband to see her hair, and therefore she is required to cover her hair even in the privacy of her home, when her husband is around. [Thus, even those who are lenient against the Talmud and Zohar to uncover their hair at home, would be required to cover it during Nida times.] However, it is permitted for a wife to uncover the sideburn areas and neck areas of her hair, when privately at home even at times that she is a Niddah, and even in front of her husband. [However, some Poskim rule that according to the Zohar who prohibits to reveal any hair of the head, this hair is also included, and it is not to be revealed even in the privacy of one’s home.]
When she is alone with her husband and is not a Nidda–During intimacy and intercourse: There is no intrinsic prohibition involved for a husband to see his wife’s hair when she is pure. Hence, the wife uncovering her hair on behalf of her husband follows the same law as when she is alone at home, and hence from the letter of the law it is permitted for her husband to see her hair when she is not a Nidda, and it may be uncovered even during intimacy and actual intercourse. However, according to the Talmudic encouragement and Zoharic prohibition, this should not be done, even for the sake of her husband. This especially applies during the actual intercourse that the hair should remain covered. Thus, when the wife gets dressed up for her husband to engage in intimacy she should remain wearing her head covering [Sheital-wig, or Tichel] and is not to remove it and make up her hair even under the pretext of Shalom Bayis, or love, and intimacy. Although one who does not follow this, and uncovers the hair during intimacy, and even during penetration, does not break the letter of the law, nonetheless, they certainly lose the benefit of all the blessings discussed above, which are very much needed in every home. Even those who are lenient to uncover the hair during intimacy, should at the very least try to be stringent by the actual intercourse, as stated above, and especially if she is pregnant, or can become pregnant from it.
There is no prohibition for a husband to see his wife’s hair uncovered during times of purity. Nonetheless, based on the Zohar, women are particular to never reveal their hair in the open, even in the privacy of their bedroom. This Zoharic teaching is recorded in the Poskim, and is encouraged to be followed by all. Many blessings are stated to be given to those who are careful to abide by this. Accordingly, during intimacy, and certainly during actual intercourse, the hair should remain covered.
If one is having intimacy/intercourse completely under the covers, including the head, may the hair be left uncovered?
Some suggest that in such a case the hair may be uncovered, as there is nothing intrinsically wrong with the husband seeing her hair, but rather that it not be revealed to the walls of the home, and hence since her head is being covered by the sheet, it is permitted even according to the Zohar for her hair to be uncovered even during the actual intercourse.
May a wife uncover her hair in the shower?
Yes. Even according to the Zohar, it is permitted for the hair to be uncovered in the shower, as it is necessary for washing the hair.
May a husband take a shower with his wife and consequently see her hair uncovered?
There is no recorded intrinsic prohibition or act of piety, even according to the Zohar, against the husband seeing his wife’s hair, and hence those who follow the letter of the law allowance to shower with their wife [see Chapter 6 Halacha 4] may do so even though he will see his wife’s hair.
My husband desires me to wear out my hair during intimacy in the bedroom. May/should I do so?
While certainly this is allowed from the letter of the law as stated above, nonetheless, one is encouraged not to do so even in such a case that the husband is requesting it. Being that this is a Mitzvah that relates to the woman’s body, she certainly has the right to be stringent against the husband’s wishes, and being that this matter carries with it many important blessings she should therefore hold on to that right, and not compromise on this very vital matter. Nonetheless, the wife should explain the importance of this matter to her husband and suggest he speak to a Rav regarding it. Likewise, she can purchase a cheap set of attractive and fancy wigs to wear for her husband when they are alone and during intimacy to try to appease his desires. In all cases of dispute in this matter that they cannot resolve on their own, it is suggested that the couple to turn to a Rav or marriage counselor for counseling on this issue.
My wife desires to wear out her hair during intimacy in the bedroom. May she do so?
This follows the same answer as above, that while it is permitted to be done, it is not encouraged, and she should certainly try to respect her husband’s wishes regarding a matter that brings blessing to both her and her family. The previous mentioned suggestions can be followed in this case as well.
My head covering often falls off during intimacy. What should I do?
There are various types of head coverings that exist, and some work better than others. Some have intimacy while wearing a special Sheital’s bought for this purpose to a) help cover her hair throughout the intimacy and b) make her more attractive for her husband. All in all, one should try their best, and Hashem does not require or demand perfection in this matter, and hence if the head covering begins falling off, they should simply try to slip it back on. Some suggest that if one is completely covered under the sheet, then the hair may be uncovered, as stated above, and hence having intercourse fully under the sheet can also help avoid this issue.
May I reveal at least some of my hair in the privacy of my home, when I am with my husband?
According to the Zohar, none of the head hair is to be revealed even in the privacy of one’s home, as stated above, and hence wearing half a covering does not live up to the Zohar’s requirement. Nonetheless, it is certainly better to cover the hair at least partially than to uncover it completely.
 See Sefer Kevoda Bas Melech [Weiner] 43-53
 See M”B 75:14 and Biur Halacha “Michutz”; Ketzos Hashulchan 9:4 footnote 11
 M”A 75:4 that so is implied from E.H. 21:2 and so writes Tosafus Kesubos, brought in Biur Halacha ibid
Other opinions: Some Poskim rule it is forbidden for a woman to reveal her hair even in her own home when she is alone. [See Yerushalmi Kesubos 7:6 regarding Chatzer; Chasam Sofer 36 regarding Chatzer and house that so rules the Tur and Shulchan Aruch and Bach and Rambam; Nachalas Tzevi E.H. 21:7; Mayim Rabim E.H. 30; Biur Halacha ibid who questions proof of M”A; Kevoda Bas Melech [Weiner] p. 44-46 in name of Bach and Beis Shmuel regarding Chatzer and that the same applies regarding a house]
 Yuma 47a regarding Kimchis, that she merited to have seven sons who are fit to be high priests due to that “the locks of her hair never saw the walls of her home”; Yerushalmi Yuma 1:1; Megillah 1:10; Horiyos 3:2; Vyaikra Raba 20:11; Tanchuma Acharei 7
 M”B 75:14 based on statement of Zohar and Kimchis
 Zohar Parshas Nasso p. 239, brought in M”A 75:4 “The Zohar is very stringent that no hair be seen”; Maharam Alshiker 35; Chasam Sofer ibid; M”B 75:14
 M”A 75:4 “And so is proper to follow”; M”B ibid; Chasam Sofer 36 concludes that in our lands so is required from the letter of the law, and revealing even one hair even in private is an Erva [He writes that while the Talmudic law does not require covering in the home, the Zohar does, and since the custom of the world is like the Zohar, therefore so is the Halacha and it is forbidden to be lenient. In his words, “Since in our lands the custom is like the Zohar, it uproots Halacha”]
 Likkutei Sichos 2:319; Hisvadyus 5742 pp.2190-2191; Igros Kodesh 8:204
 See Chasam Sofer ibid; Teshuvah Meahavah 48; Kevoda Bas Melech [Weiner] p. 51 [although he omits the Chasam Sofer]
 See Admur 75:4; Michaber O.C. 75:2; Y.D. 195:7; Shiureiy Sheivet Halevi p. 264; Kevoda Bas Melech [Weiner] p. 49
 Beis Yosef 75 in name of Rashba; Tzemach Tzedek Even Haezer 139:2; Shalmas Chaim 64
 Chasam Sofer ibid; See Teshuvah Meahavah 48; Kevoda Bas Melech [Weiner] p. 51
 See Lachash in Siddur Admur in name of Zohar 3 Vasyikra 19a “Vilachfei Lei Lereishei Ulisisei Ad Shaasa Chada/And he covers his head and that of his wife’s for a moment”; Mishnas Chassidim Hashechiva 11:10 “They are to cover their heads during the Tashmish”; Kaf Hachaim 40:17; Daas Hakedusha 7:44; Kedusha Utzenius 13:2; 11:32 in name of Alfa Beisa and Geodlei Yisrael; Chosen Yeshuos 2:126; Piskeiy Teshuvos 240:24; Sheyikadesh Atzmo [Nachmanson-2015] 49 p. 483
Must the hair remain covered if the intercourse is taking place under a blanket: The seeming understanding of all the above sources is that the head of the husband and wife is to be covered by a sheet during the intercourse, and not that their heads must be individually covered by a Kippa and Tichel. Hence, some learn that covering the head/hair is only necessary when their heads are not covered under the sheet, while if it is anyways covered by the sheet, then there is no need for her to additionally cover her hair, as the entire issue is only that the walls of the room don’t see her hair, and not that the husband not see it. [Sheyikadesh Atzmo [Nachmanson-2015] ibid footnote 1]
 Sheyikadesh Atzmo [Nachmanson-2015] 49 p. 483; see previous footnote!
 Pashut, and so is implied from the ruling of Tznius that it does not apply to a bathhouse. See Admur Basra 2:2; M”A 2:2; See also Tosafus Yisheinim Yuma ibid; Kevoda Bas Melech [Weiner] p. 52
 The Reason: An exception to the above rule of modesty is by a bathhouse or river, as in these places it is common to walk around naked, and it’s not possible to be clothed. Thus, being unclothed in such a place does not break the code of modesty. [Admur ibid]
 See Igros Moshe E.H. 4:12 for a similar argument regarding that a husband cannot force his wife to be stringent to not wear a Sheital but rather a Tichel