20 CFR §222.16

1. (a)Living in the same household means that the employee and spouse customarily live together as a married couple in the same residence.
2. (b)The employee and spouse are also considered members of the same household when they live apart but expect to resume or continue living together after a temporary separation.
3. (c)If the employee and spouse were separated solely for medical reasons, the Board will consider them “living in the same household” even if the separation was likely to be permanent.