Insulation, Radiant and Vapor Barriers - Insulating bathroom - Please help

I haven't received an answer for my question about insulating/soundproofing my new bathroom and I was wondering if anyone can help.

Here's my original post:

I had a new bathroom roughed in recently and I want to insulate it before hanging drywall. I live in a rowhouse and the bathroom is situated on an interior wall on the second floor so I understand that insulating it probably won't keep the temperature more moderate. My main goal is soundproofing the room.

In addition, the ceiling is framed about 2 feet below existing ceiling and roof. Will this cause any problems because there will be dead space up there?

Any suggestions on insulating/soundproofing this bathroom?

Thanks!

Between 2 conditioned spaces you do not have to insulate and if you decide to install insulation between 2 conditioned spaces you do not need a vapor barrier. This is the standard rule with insulation and vapor barriers.

In your case you will install insulation with a vapor barrier between 2 conditioned spaces. The reason for this exception is because of the high humidity associated with bathrooms.

With the drop ceiling. Again you are going to install the insulation with a vapor barrier. The dead air space between the drop ceiling and attic is really not a problem. Unless there is insulation in the attic and it has a vapor barrier. It is the vapor barrier on the insulation in the attic that is going to trap moisture in the dead air space in the drop ceiling. Remove the vapor from the insulation in the attic to avoid moisture from being trapped between the 2 layers of insulation. It is also important to insulate the walls of the drop ceiling.

In other words, every wall and ceiling of the bathroom must have a vapor barrier and insulation. If you leave a small section of wall or ceiling uninsulated and without a vapor barrier, that section will have a high probability for moisture problems.

Even with the wise and judicious use of insulation and vapor barrriers, don't forget to provide adequate exhaust ventilation to remove the moisture.