This is something you never want to happen when you’re renovating, but will doesn't seem to be enough to keep it away. Recently, we found rot when replacing the front door. A small project that is the cherry on the top for a much bigger renovation. But where do you stop? Replacing a door can become a much bigger project.
I have some rules of thumb that I follow so I don't get carried away. These are the questions I ask myself to decide whether to keep uncovering, or whether to clue up the project and move on to the next thing.
Does it fit the scale of the project? If you have all of the clapboard off the house and are staring at rotten sheathing (the stuff under clapboard) replace it. It’s unlikely you’ll get another opportunity in the near future. If you’re just replacing your front door (like us) and find a rotten sill, keep going down this list of questions.
Is it wet? That’s a good way to know if water is actively coming unto the house, or “penetrating the envelope.” If a piece of wood is wet, it needs to be replaced. This is also a good indication that you need to investigate what caused the water to get in. It’s easy to get overwhelmed in these situations and think that you now need to do a big scale renovation. That’s not always the case. Sometimes it’s as easy as adding a piece of flashing.