I am trying to better insulate a bedroom in our home that gets colder than the other rooms on the second level. I am experimenting with insulating the windows to see if that does the trick. While doing so, I noticed what appears to be rot on the interior of the frame (see image below).
What might be causing this, and how do I fix it?
It looks like the sash is rotten behind the molding. This could be due to condensation from the inside, or due to water ingress from the outside for instance if there is a bad seal.
The steps and complexity of this repair depend on what you will encounter when taking the window apart.
The repair involves removing the molding and the pane, scraping or cutting away the rotten part of the sash, fitting new timber (custom cut to shape and length) to restore the sash, and reinstalling the pane with the molding.
This can take a whole day and is not a beginner job since it likely involves restoring the sash. If the rot is only in the molding, a beginner could do this.
It is best to prepare a work area where the window can be placed on a flat surface to be worked on.
You can begin by carefully removing one of the moldings to more accurately determine the extent of the rot. With one molding removed, poke very carefully around the pane, with a screwdriver or utility knife. This can be done with the window in place and will not expose the room to the elements. Update your question with your findings.
