Wood rot is a moisture problem that learned to eat your framing.

Rotten Wood: diagnosed and explained.

Rot is a fungus, and like anything alive it has requirements: wood to eat and moisture to drink. Take away the moisture and rot stops; leave the moisture and it works through your framing one fiber at a time. In most homes the buffet is the crawl space, where floor joists, beams, and posts sit close to soil that gets wet from poor drainage, plumbing leaks, or ground moisture rising in the enclosed air. The early signs are subtle: a musty smell from the vents or floor registers, floors that feel soft or bouncy in spots, paint bubbling near the floor line. Direct evidence lives below: wood that looks dark, cracked into cube like patterns, or fuzzy with growth, and framing that a screwdriver tip sinks into where it should barely dent. Rot matters because it is structural subtraction. A joist that has lost part of its cross section carries less than it was built to carry, and the floor above sags, bounces, and eventually fails to hold fasteners. It also never stops on its own while moisture remains. The encouraging part is that rot repair is well understood: correct the water source, remove what is destroyed, and restore strength by sistering sound new lumber alongside the damaged members. In Southern California, Arizona, and Nevada, the dry climate slows rot but does not prevent it; crawl spaces concentrate what little moisture there is, and winter rains or a quiet plumbing leak give the fungus everything it needs.

For the repair side of this, the foundation repair solutions page lists every method Dalinghaus installs, including the ones that fix problems other than rotten wood.