20 CFR § 416.1132 - What we mean by “living in another person's household”.
(a) Household. For purposes of this subpart, we consider a household to be a personal place of residence. A commercial establishment such as a hotel or boarding house is not a household but a household can exist within a commercial establishment. If you live in a commercial establishment, we do not automatically consider you to be a member of the household of the proprietor. You may, however, live in the household of a roomer or boarder within the hotel or boarding house. An institution is not a household and a household cannot exist within an institution. (Institution is defined in § 416.1101.)
(b) Another person's household. You live in another person's household if paragraph (c) of this section does not apply and if the person who supplies the support and maintenance lives in the same household and is not -
(1) Your spouse (as defined in § 416.1806);
(2) A minor child; or
(3) An ineligible person (your spouse, parent, or essential person) whose income may be deemed to you as described in §§ 416.1160 through 416.1169.
(c) Your own household - not another person's household. You are not living in another person's household (you live in your own household) if -
(1) You (or your spouse who lives with you or any person whose income is deemed to you) have an ownership interest or a life estate interest in the home;
(2) You (or your spouse who lives with you or any person whose income is deemed to you) are liable to the landlord for payment of any part of the rental charges;
(3) You live in a noninstitutional care situation as described in § 416.1143;
(4) You pay at least a pro rata share of household and operating expenses (see § 416.1133); or
(5) All members of the household receive public income - maintenance payments (§ 416.1142).