I had my old concrete front door stoop removed in preparation for a new granite stoop, and rotted sheathing and sill plate was found behind. The steps were 6ft wide and I doubt that the damaged area extends too much beyond this (lets say 8ft to be safe). I've occasionally seen a few big and juicy carpenter ants around the area.

The 2x6 sill sits on the concrete foundation wall, and the floor joists are perpendicular and rest on the sill. Sections of the band joist (perpendicular to the floor joists) may need to be replaced too. The sill looks pretty bad on the outside, but is not rotted all of the way through. Poking through the comprised sections reveals solid wood behind.

This area of the basement is finished with a sheetrock ceiling and panelled wall. The basement wall has a 2x4 plate on the concrete as well as a 2x4 plate up against the floor joists, but the studs (2x4s) in the basement wall don't line up directly under the floor joists.

I have had several contractors look at this and have come away with 3 basic opinions so far:

1.) One contractor says he can fully remove the sill plate a little bit at a time and install a PT replacement sill WITHOUT any jacking or support from below. This makes me nervous, but he claims to have done this "hundreds" of times with no issues. I don't know if he is assuming that the basement wall will carry some of the load while the sill is removed. Remember, the basement wall studs don't line up with the floor joists.

2.) Another wants to frame out a temporary load-bearing wall in the basement (must not trust the existing basement wall) in order to support the floor joists while the section of sill is replaced. This is considerably more expensive. Note that he didn't mention using jacks, only lumber.

3.) A 3rd says there that the rot doesn't appear to go all the way through the sill (i.e. only ~2" deep), so he wants to clean it out as best as he can and reinforce with additional PT lumber tapped in from the outside.

Everyone is planning to install new sheathing with ice and water shield. The new granite stoop will have ~1/4" space between it and the sheathing and will be pitched slightly forward to direct water away from the foundation.


I don't plan on doing this myself, but I still want to understand EXACTLY how this repair is going to be made. I'm not sure who to listen to. #2's approach seems the safest, but he also wasn't very willing to entertain detailed questions (relative to the other two), and just didn't seem as interested in taking on the job.

 

As always, pictures paint a better picture than words, so if you can post a couple so we can see what you see and what your contractors saw, it would be a big help.

If the inside basement walls were built as independent walls, they should afford lift so a repair can be made from the outside. I really don't see a need in building a false wall since there will be one only a few inches from him, already in place. Sometimes sills aren't rotted all the way through, and can be repaired and new band put in place with all the preventative stuff you mentioned and all will be well. I would caution against mold and deep rot, though, as it should be taken care of. The basement walls don't necessarily have to line up with the studs. They should have a double plate on top of the studs that will span across it all for support.

Hang in here and post the pictures. Others will definitely chime in with other ideas once the pictures are posted.