Moisture Control

 

Water and Soil

Residential ground surface storm drain systems must transport excess moisture away from designated areas where excess water would otherwise prevent the normal use of a residential property. If rainfall is allowed to pond or collect adjacent to a structure built on expansive soil, the structure may be subjected to unscheduled distress caused by swelling bearing soils due to increased soil moisture content. In addition houses with a basement are subject to moisture infiltration during heavy rains and wet periods. Likewise, perpetually moist ground surfaces limit recreational use of residential yard areas, and can become a breeding ground for disease carrying insect infestations such as mosquitos. Water must freely exit the property to assure unrestricted, healthy, and environmentally safe use of land areas within residential property boundaries

 Soil Moisture

If expansive, the foundation support soils expand and contract due to changes in moisture content. Changes in moisture content can cause very large changes in soil volume when going from a dry to a saturated condition, and vice versa. This movement does not mean the foundation is improperly designed or that it has failed. Uniformity is the goal: uniform moisture content in the soil, uniformly maintained in all areas around the foundation. If changes in moisture content are uniform, then movement of the foundation will be uniform and less distress will be created in the structure. If changes in moisture content are non-uniform, then there may be differential movement in the foundation. Differential movement can cause greater (and more obvious) distress in the structure. Leaking pools, leaking plumbing lines, leaking drains, dripping faucets, dripping air conditioning condensate lines, and misdirected water from clogged and broken gutters and downspouts can cause local high moisture contents that can result in differential movement in areas of expansive soils. These conditions should be remedied as soon as possible. Trees in or near the footprint of the foundation, either removed or planted during construction, cause the majority of foundation problems requiring repair in this area.

 Soil Erosion

Soil Erosion is the loss of soil from the ground surface. It is a process that is always occurring but  can happen faster if we misuse the land or if the ground surface is not adequately protected with vegetation and drainage swales. The rate of erosion can be increased by removing or limited plant cover, poor grading plans, wind, frost and rain and water runoff. Two of the most common types of soil erosion are water and wind erosion. Water or splash erosion is the detachment and airborne movement of small soil particles caused by the impact of raindrops on soil. Sheet erosion is the result of heavy rain on bare soil where water flows as a sheet down any gradient carrying soil particles. Where precipitation rates exceed soil infiltration rates, runoff occurs. Gully erosion results where water flows along a linear depression eroding a trench or gully.

 Exterior Grading

The soil around a home needs to be sufficiently sloped or graded to drain runoff water away from the home. It is extremely important, particularly in areas of expansive soils, that water drains away from the foundation and not be allowed to pond against or near the foundation. Inadequate drainage and grading around a building, and especially those without hard surfaces and surface drains to direct water away, can effect the foundation. Uncontrolled roof rainfall runoff can erode the ground surface along the foundations perimeter and provide a source of excessive and non-uniform water input into the foundation perimeter beam bearing soils. Variances in bearing soil moisture content distribution along the foundation perimeter can result in unscheduled foundation system, vertical displacement, and rotational movement.