This week I learned how to repair a sash cord. We own a 120 year old victorian and, not surprisingly, the sash cords have started to go. I found this webpage very useful, as it has a video showing what you'll need to do.
The first cord we repaired took about an hour and a half. I had to stop about 15 minutes into the job to nurse my youngest son, and my parents took over for me. The next two windows I did with the help of my older son, Otto, and they took 45 min and 20 min, respectively. Not bad for a job that's described by some as "one of the hardest repairs a homeowner will ever do!" Ha to that!