MANAGING EXTERNAL WATER
Neglecting moisture and water problems in and out around dwellings can produce conditions that support mildew within the house and wood-destroying fungus attack the structural members. Management of both surface water and moisture vapor can prevent the conditions required to support mold and fungi growth. Some of the most common external moisture problem areas and their suggested solutions follow.
Lot Drainage
The grading and landscaping plan for every dwelling should provide control of surface water on the lot. One minimum standard requires a 2 percent grade sloped away from the house in all directions for a minimum distance of 10 feet, or about 2�-inch drop in 10 feet. This is intended to prevent surface water from collecting alongside and under the house.
It is not unusual for the lots of the houses about 25 years old and older to need a complete renovation of the landscaping and grading. Additions to the landscape plan, maturity of shrubbery and some soil erosion tend to change drainage patterns and direction and too often surface water meanders against a foundation wall.
Figure 11 illustrates the most common drainage problem of a sloping lot. The uphill side of the house must have a drainage waterway (valley) to conduct the water around the house. This drainage valley should be at least 10 feet away from the house and sloped to conduct the accumulated water away from the dwelling efficiently.