Break contact of wood and soil. Where soil must contact wood, use properly pressure treated lumber. The odor of mold and mildew inside the home is a sure sign of condensation and dryrot. Warm weather condensation can be reduced with fans and by decreasing the humidity of crawl spaces with adequate ventilation. When mold and decay occur, the problem is either water conducting dryrot or dryrot growing on wet wood.
Water conducting dryrot feels leathery and can often be peeled off in sheets.
The other form of dryrot feels powdery or stringy. The only way to get rid of molds and decay fungi embedded in wood is to remove the piece. Frequently extracting a rotted structural piece can be an expensive proposition. Prevention is far cheaper. A common source of dryrot is wood decks.