Working in my old home today (we were gutting the failed plaster walls) we came across what appeared to be at first some minor wood rot. Well, we kept going and boy, were we horrified to find that much of the wood was rotten, all the way from the interior, through the sill and bottom of the case, through the stud the sill was supported by, and partially through the wall planks (almost through the exterior. There were also some ants in there (assuming carpenter ants -- you can see their tunnels in some of the pictures below). My guess is that someone did a poor job with the replacement windows, which in turn let the water in, rotted the wood, and made a nice home for the ants. I've already removed the ants (vacuumed out as many as I could along with the failed wood) and fumigated them. I'm convinced they are gone but I want to make sure they are gone to stay and also have repaired the damage.
So, my question is -- is fixing this something I can consider on my own? Frankly I'm a big scared at the the seriousness of the job, but on the other hand it seems like something that I could probably handle if I knew the best way to go.
Any suggestion? I'd like to keep as much of the original window and case as I can, but not at the cost of a sound structure.