I'm refinishing my basement, and I'm not sure where I should install a vapor diffusion retarder (i.e. plastic sheet) on the framing I'm about to put up. Here's my situation:
-Right now my basement is almost completely unfinished.
-I'm installing framing along the cinder-block walls the separate the interior of the basement from dirt.
-About two years ago, I had a sump system installed. This is the type of system where they jackhammer out the entire perimeter of the basement, install a drainage pipe (which in my case leads to two sump pumps), pack it with gravel, and cover it over with concrete. A mirror drain is installed along the edge of the wall as well.
-My system is very active. Each of the two pumps fires about once every ten minutes, almost all year round, and will each fill up a 50-gallon rain barrel within a day. We could maintain a rice paddy if we wanted to. During heavy rainstorms they turn on perhaps once a minute.
-My basement has remained pretty dry. I have a dehumidifier with a sensor that reads around %55 in the summer, and there aren't any leaks I have noticed, yet.
Conventional wisdom says that you should put the vapor diffusion retarder on the warm side of the wall, which would be the interior in my case (I guess I could just install drywall that has a plastic membrane in it). However, I have this very active sump system open to the area along the wall via the mirror drain. This makes me think that there will be lots of vapor trapped behind the wall if I just put the diffusion barrier between the framing and the drywall, or just use vapor-retarding drywall.
Any ideas about how to handle this? Should I hang plastic sheeting along the cinderblock wall, and tuck it into the mirror drain, or should I install a barrier along the back of the framing, where it is closest to the cinderblock wall?
Thanks for any advice you can give. My google skills haven't turned up anything that looks like a satisfying answer.