Kiddishin 81a - Yichud

The Chochmas Adam (126:7) says that when there are 2 rooms, one outer and one inner room - if a man is in one and a woman is in the other, it would be a machlokes rashi and rambam whether this is a yichud problem. In the Binas Adam (18) he elaborates. Rashi says that the case of men on the inside and women on the outside, or the opposite, is assur because it will lead to yichud. Rashi implies that the issur is not for the man to go in to the place of the women, but even to set up a situation which will lead to yichud if the man will go into the women is assur. However, the Rambam understands that the issur is only when the man actually goes into the area where the women are present, but the set up of a situation which will lead to yichud, is not yichud.

It seems that this machlokes would also apply to a house when a man and woman each go into separate room in the same house. Under the present state there isn't any yichud, but since it can easily lead to yichud by the man or woman leaving their room, rashi would hold it is assur to set up such a situation. The Binas Adam suggests that even the Rambam is only lenient because there are many men and women in the gemara's case, but in the case where a man and woman are alone in a house, being in separate rooms would be an issur yichud even according to the rambam. But, he then rejects it, and assumes that the rambam would be meikil so long as each stays in their private room. He considers this a safeik hashakul, and is therefore lenient by yichud with a p'nuya which is only d'rabonon but is machmir with yichud of a nidah which is d'oraysa.