Introduction

Introduction

The grade and the drainage system around a house consists of two complementary components. Grade must be established near the home to: (1) separate framing and wall covering materials from earth and hard surfaces such as driveways, and (2) divert water away from the foundation. Grade must be established on land near the house to make sure water flows away from the house and toward appropriate points either on or off the land. We address separation between building materials, earth, and hard surfaces in the wall covering section.

Establishing and maintaining means to divert water away from the foundation is essential for several reasons. water that enters into crawl spaces and basements can damage wood structural members, insulation, and finish materials, and can provide moisture for fungal growth. Moist soil near the foundation can provide a hospitable environment for some wood destroying organisms including termites. Moist soil contributes to problems such as frost heave and soil expansion.

Water can severely damage the foundation walls, footings, and concrete slabs causing problems including cracks, bulging, rotation, lifting, and deterioration. Water pressure against the foundation walls is a common cause of foundation damage. Water that freezes near the foundation can expand causing frost heave.

Water can cause some unstable soils (such as expansive clays) to expand and contract. Soil expansion against foundation walls increases pressure on the foundation that can cause damage similar to water pressure. Soil expansion under the foundation can lift the foundation and with it the entire house. Soil contraction under the foundation can cause the foundation to sink and with it the entire house. Damage from water pressure can occur almost anywhere. Damage from unstable soils is more common in certain areas of the country such as the Southwest.

Natural slope away from the foundation is the ideal means for diverting water away from the foundation. Other means of diverting water (such as swales and underground drains) are acceptable if natural slope is not practical because of nearby structures, impediments such as hills and vegetation, or because the natural slope of the land is toward the foundation. Earth should slope away from the foundation at least 6 inches in the first 10 feet. Hard surfaces such as concrete should slope away between at least ⅛ – ¼ inch per foot. When earth slopes toward the foundation, swales or other grading systems should be established such that water is diverted around the foundation.

Land should be graded so that water is not diverted on to neighboring land unless the water flow is part of the natural grade. For example, water from a higher lot may flow on to a lower lot, but the higher lot should be graded so that the water’s impact on the lower lot is minimized to the extent practical. Houses on low-lying land often have water problems including flooding basements, flooding crawl spaces, and erosion. Home inspectors should be aware of a house’s position relative to surrounding land and may wish to report potential water problems caused by runoff from neighboring land.

It is possible to have too much slope away from the house as well as too little. It is also possible to have too much slope toward the house. Steep slopes are prone to landslides that can cause major damage. The distance between a house and the beginning of a downward slope should usually be 40 feet or H/3 where H is the height of the slope, whichever is less. The distance between a house and the beginning of an upward slope should usually be 15 feet or H/2, whichever is less. Reporting houses that do not meet these guidelines is a judgment call. The foundation may have been designed to allow placement closer to the slope or the building official may have approved the placement. Absent visible defects caused by excessive slopes near the house, a warning in your report may be all that is necessary.