My bathroom is built under the stairs. Curving stairs are above part of bathroom ceiling, and rising to upstairs hallway.

In the space where the stairs rise, I suspect there is a small dead air space between the stairs and bathroom ceiling. Over the years paint cracks and peels and black stains appear, just under that space. Sc**** it, fill and paint it, looks great for awhile but after 10 years the problem is back full force.

If there is a dead air space, I suspect same problem that occurs in uninsulated attics -- moisture is being condensed out the air in winter.

Has anyone had this problem?

How did you / how would anyone suggest fixing the paint and stains problem? Do you think I have a space? Any help appreciated.