Apex Window Werks repaired window sill and sash, Chicago IL
Due to a neglect of routine maintenance, and/or other factors including that the window was on the outside of a high apartment window so perhaps went unnoticed for a while, this window suffered extensive water damage from rainwater and moisture seeping into the lower sash and window sill. This damage occurred over some time and the swelling of the wood allowed for it to stay damp for longer periods until it completely disintegrated. As you can see from the image the face of this building is highly exposed to weathering so damage is probably occurring on other windows of the building too.
In order to repair this window, the lower window sash had to be replaced and the lower brick molding replaced and then painted. The seals were also replaced and the leaks sealed, caulked etc. (the image was taken before the final clean up and coat of paint).
It is vital to repair your damaged windows as soon as possible as damaged and perished seals and frames allow cold air to get through the closed windows which can result in much higher electricity bills from heating required in the colder months of the year. If you leave the windows to continue to deteriorate it may end up requiring the entire window to be replaced which is extremely costly, as well as detracting value from your property and potential risks from mold and insect infestation. Make sure to find a trusted professional to repair your own windows.