Foundation Maintenance & Monitoring Program


Proper care of your foundation is very important in preserving the integrity of the structure. Soils have the ability to expand (when wet) at alarming rates. This requires that an even and relatively constant level of moisture be maintained in the soil supporting the foundation. Defects in foundations occur when the supporting soil is too wet or too dry or when one area around the foundation is overly wet, while other areas remain dry. Improper foundation maintenance can result in severe movement in just a few days. This is true regardless of the type or age of the foundation. To avoid additional foundation problems, you must avoid non-uniform moisture content in the soil supporting the foundation. Non-uniform moisture content can be caused by any of the following:

  • Improper drainage
  • Allowing the soil to become dry
  • Excess watering near the foundation
  • Plumbing leaks
  • An improper watering program
  • Neglect
  • Runoff water not properly diverted away from the foundation
  • Trees and large bushes growing too close to the foundation

For more information please see the following Canada Mortgage & Housing article: “Understanding and Dealing with Interactions Between Trees, Sensitive Clay Soils and Foundations”.

Additional information on all of these items can be obtained in the excellent reference, So Your Home is Built On Expansive Soils, A Discussion of How Expansive Soils Affect Buildings, edited by Warren Wray, Ph.D., P.E., published in 1995 by the American Society of Civil Engineers. This 54-page booklet can be obtained for approximately $20.00 by calling ASCE publications at (800) 548-2723

The following suggestions are essential to an effective foundation maintenance and monitoring program, and should be followed carefully:

• Drainage

• Watering

• Living with Expansive Soils

• Soil Moisture Changes

Drainage

Maintain the grading and planting beds around the foundation to slope away from the structure. The soil around a house will tend to settle with time and additional topsoil may be needed. Use a clay-based soil any time you replace the soil around the foundation. A clay-based soil, properly placed, will shed rainwater away from the foundation. DO NOT USE SAND. Sand is porous. Rain water flows through the sand into the soils supporting, and adjacent to, the foundation, where it can cause problems.

For slab foundations, it is best to keep at least two to four inches of concrete showing below the brick or siding. Soil above the brick line will allow water to penetrate into the house where the water can cause damage to the interior.

Avoid bonding or standing water in the area of the foundation. The yard should have drainage channels (often called swales) to route rainwater away from the structure. Do not add fill dirt to change or alter these drains. Gutters should be maintained and free of debris. All runoff water should be diverted away from the foundation. Watering on a regular basis can be of benefit because it can help maintain a moisture balance between the ground under, and the ground around the foundation.

Watering

If the soil along the exterior becomes excessively dry, it will shrink and crack. These cracks admit air, which causes more evaporation and more cracking. When heavy rains come, these cracks allow excessive amounts of water to go directly to the bearing levels, causing settlement. Eventually the foundation will crack and sink. If you notice the soil shrinking away from the foundation and forming a gap, it is a sign that the soil needs water. During heavy rains or excessive watering of plants, these cracks also admit water, which may erode soil from beneath the foundation, making the problem worse.

Whether you have a sprinkler system, above ground water system, or underground watering system, you should monitor the system on a daily basis. Readjust the system when soil cannot hold any more water (when water is no longer absorbed into the soil). Trees and large bushes use large amounts of water and must be placed such that damage sure to moisture loss, as well as excessive root growth, is avoided. You should add extra moisture as necessary to areas, which naturally remain dryer, such as gabled ends, adjacent to large trees and bushes, or at recessed entryways.

Diligent attention to moisture content and water movement around your house will help delay or even prevent future foundation problems.

Living with Expansive Soils

Expansive soils can create damaging movements (shrink and swell) to foundations and structures. These movements originate from changes in soil moisture. Providing uniform soil moisture next to and under your foundation is the single best thing you can do to reduce or minimize the effect expansive soil movements have on your structure.

Soil Moisture Changes

Observing soil moisture changes foundation is possible, but what about under it? Moisture can move from outside to under your foundation through a property of soils known as suction. Soil suction is similar to placing just a corner of a dry, compressed sponge in contact with a puddle of water. In a short volume. While a water source is present, the sponge will continue to absorb water already in the sponge will distribute itself evenly, but the sponge will not reach saturation.

Water can move horizontally and vertically through the soils under your foundation in a similar manner. As clay soils draw water to themselves, they too grow in volume (swell or heave) causing your foundation to move. Drying outside your foundation reverses the process. The moist soils will lose volume (shrink) as soil moisture moves out from under your foundation causing the foundation to settle. Shrinking and swelling soil motions can lead to damaging your foundation and structure. Uniform changes in soil moisture are less damaging to your structure than localized changes.

Several sources of soil moisture changes are provided in this downloadable troubleshooting table (PDF). You should review the list and possible actions to control or minimize the various sources. Begin practicing the suggested actions as soon as possible to improve your foundation and structure performance. Many of these actions can become a routine part of your ongoing conscientious owner maintenance activities. Annually inspect the area within 5 feet of all sides of your foundation after a rain to determine if proper drainage is maintained away from your structure. Monitor existing cracks for progressive or seasonal movements. Some of the possible actions, suggested in the accompanying table, will require an expert for assistance.

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