Foundation sill rot: what to do?
I discovered that my c.1895 house has some sill rot. When I bought the house 1.5 years ago, the inspector noted that much of the basement window framing had had old termite damage, but that it was long ago and didn't have a current infestation problem (the window frames had become partially buried in dirt from un-managed turf buildup). He inspected the sill in various places and it check out fine. He told me if I replaced the windows everything would be fine.
I just embarked on replacing the windows myself, with vinyl hopper windows and pressure treated framing. I successfully replaced the first of three, and indeed, the frame rot was extensive-- what appeared to be intact 2x6 was mostly hollow inside! After removing all the framing and re-pointing any newly exposed voids in the brick mortaring, I reframed with new pressure treated 2x6.
After removing the old frame, I did notice a small section of sill above the window framing that was rotted. I would estimate the area to be about 10" long by 4" wide by about 1" of penetration into the wood. The rot is focused right above one of the vertical ends of window frame, and on the inside portion of the sill facing the basement, not the outside. I suspect termites had continued past the window frame and into the sill. I suspect termites because there is no moisture or water damage to that area; I also suspect the inside face of the sill was rotted rather than the outside because the basement was always damp. The sill is not in an area that can get water, but the window frame below it did routinely get wet (being submerged in dirt!).
In addition to reframing the window, I've also dug and re-landscaped the area around the window, so there is no chance of continued moisture around the window, and the house has been inspected twice now for termites, with none found. Also, the basement air is now very dry and has a dehumidifier running year-round.
How critical is it to repair this section of sill rot? And what are my options if repair is called for?
Thanks in advance!