The above picture is taken from my parents’ 200 year old farm house on Cape Cod (http://www.saturdayfarm.com/). The original panes have a unique character as gravity has taken hold of the glass over the centuries. My parents say they will never replace them. In many historic districts (like the Montford District here in Asheville) there are rules that limit homeowners from changing or upgrading their windows. For owners of historic homes storm windows might be the best way to keep their houses more thermally efficient.
These storm windows need to be monitored and adjusted throughout the year. The weep holes need to be kept open (not painted shut!) to allow the condensate to exit without damaging the wood. Sometimes the storm windows need to be opened or removed for ventilation depending on the time of the year.
Storm windows are not ideal but in historic homes with regular maintenance and monitoring they are a perfectly good solution.
The picture below is from a house I inspected last week. It was built in 1995. The windows don’t have any historical value. They are cheap single pane windows. In this example, storm windows were installed on the INSIDE of the house in order to keep the house warmer. Let’s look closer:
When the cold air passes through the thin outside window and hits the warm air of the inside storm window CONDENSATION results, but this time INSIDE the house. You can see the damage from the moisture in the picture below. Also if you want to open the window you have to open the storm window first. This is not ideal.
Storm windows are only perfect for historical homes. In other homes storm windows may be cheaper to install but i would rather have 1 new double pane window than 2 storm windows over single pane windows.
In this house, if it can be afforded, all the windows should be replaced and the storm windows permanently removed.