Fixing sill plate and rim joist undergrade

TedF

We just moved into a home late last fall. The home was built in 1978 part on slab part on crawl. A master addition was added in 1996. This is on a crawl space (cinder block). Myself nor the inspector caught the problem I found while trying to figure out why the master room / floor was cold. The builder, I assume to match up the floors between rooms, put the rim joist and sill plate under grade. That’s right both under ground. They are not rotting yet but are both very wet (I am not sure if he even used pressure treated wood). What should I do. My first thought is to remove the soil around the additions three sides, somehow dry out the wood then cover/coat it with a water proof material (don’t know what). Then put in drain tile and fill it back in with soil. Does anyone have any ideas and or material suggestions. As for the original issue of cold floor, the plywood subfloor looked OK (not wet or rotted) when we were putting hardwood down in that room. Could the subfloor that is behind the vinyl siding be getting air in that way? Please help. Thanks, Ted

VaViaCo

You have it right with the drain tile and gravel but after that is done replace dirt only below the wood.
Cover the wood with something like tyvex and siding and leave it above dirt level.
Let warm air and sunshine dry the wood out, it won't be in dirt anymore.
(to bury beg for termites, not to mention rot. Or code violations)

Is the floor insulated? There ought to be fiberglass insulation between the joists and preferably some sort of soffit (vinyl is cheap) to hold it in place.

TedF

I am not sure I have a choice about leaving the wood above dirt level. The grade is very flat and the rim and sill are below grade. Do I have to create a step down from the top grade to below the rim?

The floor is not insulated. The crawl is encapsulated (was open when purchased and very wet). What do you mean by soffit as related to the floor (I understand the term for roof apps)?

Ron6519

Post a picture of the exterior of the house where this condition exists. If 3 walls are involved, then 3 pictures.
Ron

VaViaCo

Soffit under the joists to hold the insulation in place and keep animals out of it.
The grade needs to be fixed to keep dirt off the wood.

jogr

Your Home Inspector really blew it. I hope he's insured because he should be held accountable financially for fixing this. If you can't regrade the yard so it slopes away from the house and so that the grade is 6" below the top of the cinder block then it gets a lot tougher.

I have seen similar posts where one suggested option was essentially to cut your floor joists back so you can replace the rim/band joist with 4" thick block. The floor joists sit on a PT sill on the remaining 4" ledge of your existing 8" block and the wall sits on a PT sill on the new block. This sounds difficult but perhaps feasible if an 8" height gain is all you need.

Wood foundation technology might also work.