We just purchased a house and are in the process of finishing off the basement and have a problem with one section of the house. The house has a walk out basement with a block wall, with half of the basement wall being wood. One section of the house where the wood wall is happens to be underground and get's wet when it rains. Unfortunately this area is under the front door where a deck is so it is not accessible. There were a couple other areas on this house where the corners of the wood wall was underground and we were able to dig them up, fix the grading, and replace the rotted wood. I attached a picture that might explain things better.
So.. is there anything that can be done to prevent this section of underground untreated wood from rotting - and keep the moisture out without tearing up the deck? We cannot get to this area from the outside because of this enclosed deck / porch area.
There is no magic bullet to solve this type of problem. Wood framed walls below grade are a no-no for a multitude of reasons. Water rots the wood and rusts the fasteners. Even pressure treated lumber rots, only less quickly. Termites travel underground and eat the wood. Mold and mildew eat the wood and cause odors. Damp wood looses its shape and its ability to carry vertical or horizontal loads. It's a never ending maintenance problem.
You can spend a lot of money trying to damp-proof the outside of the wall, but that ground water is there 24/7/52 and only needs the tiniest hole to penetrate. Once inside it's guaranteed to do damage before you get around to re-repairing it.
You probably don't want to hear this, but your best solution is to excavate outside and replace the below-grade portion of the wall with damp-proofed masonry. Based on your sketch, you may need to remove-and-replace part of the porch in the process.
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