condensation on windows

I rent the upper unit of a 1920's duplex in St. Paul,
Minnesota. I moved in seven years ago. The windows are the original double-hung windows with an aluminum frame storm window. After one winter, an energy audit was done and insulation was added to the attic. In the past I had problems with moisture in the bathroom. Two years ago, a bathroom exhaust fan, which is vented through the roof was installed in addition to a new vinyl window. I use the fan when showering. I no longer have mildew problems in the bathroom, but I have noticed a small amount of condensation and ice on the inside. I have an indoor temperature and humidity gauge. Generally, gauge reads "L" (I think it has to reach 10% before registering a number), although I have seen it measure up to 25%. Therefore, it doesn't seem as though there is too much moisture in the air. Over the past few years, I've noticed that the glazing around the window panes continues to deteriorate and fall out. Furthermore, condensation, frost and ice appear on both the inside windows and the outside storm windows. However, this DOESN'T occur in the downstairs unit. This winter, the wood, double-hung bedroom windows (which face west) were re-glazed. We also added bronze spring weatherstripping to the inside sashes. I thought that would take care of the condensation, frost and ice - but no! I continue to have nearly totally frosted storm windows and condensation on the lower edges of the inside windows. What do we do next? And, why doesn't the downstairs unit experience the same problems?

Thanks!

 

Condensation and ice on the interior windows is a result of warm moist air contacting the colder surface of the window panes. The degree of the occurance depends on the percentage of humidity in the air and the exterior temperature. Even with the lower humidity levels you describe, it can still occur on those extreme cold Minnesota nights. Air movement, or the lack of it around the windows can also be a factor. Drapes or window screens can trap the air giving it added time to cool & condense. Increasing the inside temperature a few degrees may help a bit. The frost on the exterior storm sounds like air leakage. You have weather stripped but leakage may also be occuring around the window frame. Caulk around the window casing. Consider removing the casing and check to see if there is insulation between the window frame and rough stud opening. You may be experiecing the condensation problem more than your down stair neighbor because of your improvements and air sealing. The tighter the envelope the more humidity remains in the house. The weather whistles right through a leaky home.