Question about adding lean-to greenhouse to existing wall
I posted the following issue in the Greenhouse Forum, but didn't get much in the way of informed replies, so I'm re-posting here. Any thoughts would be appreciated.
I live in the Pacific NW and the winters are mild: most of the season it only goes below freezing for a few days. I have a friend who wants to construct an attached, lean-to greenhouse against one wall of his house. It would consist of a cedar frame and salvaged, double-pane windows and a sliding glass door, all with aluminum frames. The footprint would probably be about 8' X 10' or 8' X 12'. The backside of the greenhouse would be a south facing wall. This wall is a garage wall clad in horizontal wood siding; it is insulated, there is a tarpaper moisture barrier, and there is finished sheetrock on the inside wall. The garage is unheated, but there is enough heat from some exposed ductwork that the garage never goes below freezing.
Here is the issue. He wants to attach the structure directly to the existing exterior wall, but I suggested to him that he should research whether he might end up with some kind of moisture problem within the wall. Can anybody advise on whether this is something to worry about? And, if so, what is the best way to deal with this? The greenhouse will not have much, if any, supplemental heat; however, it will have moisture, and the temperature inside it could range from below to well above the ambient temperature inside the garage, based on time of day and how much solar gain there was on a particular day.
Finally, it would be nice to have a solution that looks decent when finished, so something like just slapping up a piece of Tyvek on the wall is a less-than-ideal final solution.