On our house, the sill is bad in one spot that is about 3 meters long. The entire sill is not rotten, only about 3cm up from the "bottom" and about 7cm in. I measured this in the worst spot I can see.
Can you replace just this part or do you have to replace the whole thing? The reason we want to avoid replacing the whole thing is that the floor joists are notched into it, and we are unsure if we can handle that... The floor joists are undamaged, and so are several centimeters of the sill around them.