Le-khatḥila, a married man must build a sukka where he and his wife can both sleep. Even though women are exempt from the mitzva of sukka, a woman who sleeps in the sukka fulfills a mitzva. Moreover, if the spouses sleep separately, it diminishes their festival joy. Thus, it is proper to build a sukka in which both spouses can sleep (above, 2:14; Harḥavot 2:14:5).
If it is impossible to prepare a place for the wife to sleep in the sukka – for instance, if the sukka is too small, or there are other men who need to sleep there, and they cannot build another sukka just for the couple – and the couple is mitzta’er when they sleep apart, some say the man may sleep in their bedroom at home. This is because the mitzva of sukka is for a man to sleep in the sukka in the way that he normally sleeps in his home, which is with his wife. If they cannot both sleep in the sukka, he is exempt (Rema 639:2). Others say that the man is exempt only if the couple are truly mitzta’er when they cannot sleep in their bedroom (MA ad loc. 8). Still others say that a married man has the same obligation to sleep in the sukka as a single man, and even if he is mitzta’er from sleeping in the sukka, apart from his wife, he is still obligated to sleep in the sukka. Only on special nights (such as when he and his wife will fulfill the mitzva of having marital relations with the regularity to which they are accustomed) is he exempt from sleeping in the sukka (Vilna Gaon; MB 639:18).
In practice, if one is truly mitzta’er when he sleeps apart from his wife he must invest effort and money into building a sukka where they can be together. If it is very difficult for him to do so, he may, if he wants, rely on those who are lenient and sleep inside.
Rema in Darkhei Moshe writes that one who trembles at God’s word will try to build a sukka where he and his wife can sleep, and thus serve God with joy, and that this is the custom of those who are meticulous. This is also the view of Derekh Ha-ḥayim; SAH; Ḥayei Adam; and others. Nevertheless, it would seem from the poskim that there is no obligation to spend a lot of money to build an extra sukka where he and his wife can sleep. The reason seems to be that since the sukka is a temporary residence, one needs to invest in it only what he would invest in renting an apartment for a week. It should be noted that, privacy permitting, it is permissible to have marital relations in a sukka (BHL 639:1 s.v. “ve-al”).