Site drainage has an enormous effect on your home’s foundation’s performance. The initial builder should have established proper site grading around the foundation when the house was built. Positive drainage should have been provided away from the foundation regardless of whether the soil is expansive or collapse. You might want to learn about Building Codes For Drainage Around A House for a better understanding. This drainage scheme should be maintained during the useful life of the residence. If not, you can expect to see an adverse effect on the foundation performance.
Changes in moisture content of expansive soils are the cause of both swelling and shrinking. It is extremely important in minimizing soil-related foundation problems. Positive drainage should also be maintained in the areas where sandy soil is present.
Poor drainage at residential houses in North and West Houston can result in saturation of the surficial sands and development of a perched water table. The sands, once saturated, can lose their load carrying capacity. This can result in foundation settlements and bearing-capacity failures. Foundations in these areas should be designed assuming saturated subsoil conditions.
Things To Avoid For Foundation Performance
Many homeowners, as well as some uneducated homebuilders make an elevated berm around flowerbed areas creating a dam between the berm and the foundation. This prevents the surface water from draining away from the structure. This might be visually appealing but can cause significant foundation damage as a result of negative drainage. There are some methods to obtain this look without allowing the soil around the foundation to become saturated.
Unknowing landscapers and other non-professionals often undertake another misguided path directly affecting site drainage and foundation performance. The concern is placing planting beds next to a foundation without proper slope. We have seen many cases when inspecting new homes during the Move-in Phase where there was an apparent positive drainage. But, after taking a closer look we found the planting area was elevated with sand placed on top of the expansive soils. In doing so the drainage was not effective. Foundations can also move excessively when builders remove trees next to a foundation without compacting soil into the hole.
Maintenance For Site Drainage And Foundation Performance
All components of your home require maintenance for site drainage and foundation performance. Your foundation is no exception. It requires regular maintenance to prevent foundation failure. To ignore those needs puts the foundation into distress.
Depressions or other water catch basin areas can occur where roof drainage is uncontrolled. All depressions should be filled with compacted soil. Use sandy clays or silty clays, not bank sand! Remember to have a positive slope from the structure. If doing so becomes difficult, drains should be provided to promote runoff from the low areas.
Pets, especially some breeds of dogs, sometimes excavate next to the exterior grade beams and create depressions and low spots in order to stay cool during the hot season. This will result in ponding of the surface water in the excavations next to the foundation. Standing water will almost always lead to subsequent undesirable foundation movements. These movements can be in the form of uplift in the areas with expansive soils and settlement in the areas with sandy soils. As with any depression these should be backfilled with compacted clay fill.
Control Site Drainage And Foundation Performance Using Drains
Area drains can be used around the house to control site drainage and minimize ponding of the surface water next to the foundations. Doing so can minimize the drainage effect on foundation performance. The area drains should be checked periodically to ensure they are not clogged.
The drains should be provided with outlets to deposit the water well away from the foundation. In some cases, sumps will be required to collect the water and pumps to expel it if gravity drainage away from the foundation is not feasible. Sumps should be located well away from the structure. Drainage should be adequate to prevent any water from remaining in the drain (i.e., a slope of at least 1/8 inch per foot of drain or 1 percent should be provided).
Subsurface drains might be used to control a rising water-table, groundwater and underground streams, and surface water penetrating through porous or fissured and highly permeable soil. We ran into this issue with a house we inspected northwest of Houston. Drains can help control the water table in the expansive soils. However, since drains cannot stop the migration of moisture through expansive soil beneath foundations, they will not prevent long-term swelling. Moisture barriers can be placed near the foundations to minimize moisture migration under the foundation. To be effective the moisture barrier should be at least five feet deep.
Drainage Maintenance For Pier And Beam Foundation Performance
Positive drainage should also be established underneath structural slabs with a crawlspace. Absence of positive drainage may result in surface water ponding and moisture migration through the slab. This may result in wood floor warping and tile un-sticking. Whether or not this area should also be vented or not is controversial today. Unvented crawlspaces require special attention to detail related to moisture barriers, etc.
An elevated building pad is recommended prior to constructing a pier and beam foundation for a house or manufactured home. Site drainage and foundation performance are then more easily addressed. Surface water should be diverted away from the elevated crawlspace. Otherwise, piers can lose their support resulting in windows and doors not opening correctly as well as sloping floors.
Using Roof Gutters To Maintain Site Drainage And Foundation Performance.
Roof drainage systems, such as gutters and downspouts or rain disperser systems (Rainhandler, et.al.), are recommended all around the roof line to prevent adverse effects on foundation performance. Installing partial gutters does not maintain soil moisture density the same at all sides of the foundation. When gutters and downspouts are installed, they should be kept clean of leaves, tree limbs and other obstructions.
If a roof drainage system is not installed, rainwater will drip over the eaves and fall next to the foundations resulting in subgrade soil erosion, and creating depression in the soil mass, which may allow the water to seep directly under the foundation and floor slabs.
In the areas where expansive soils are present, the gutters should be connected to flexible pipe extensions, so the roof water is drained at least ten feet away from the foundations. Preferably the pipes should direct the water to the storm sewers. In the areas where sandy soils are present, the gutters should drain the roof water at least five feet away from the foundations.
Other Conditions That Can Effect Foundation Performance
Other conditions could influence your foundation’s performance besides rainwater. For instance, not having ground cover next to the foundation promotes soil erosion and accelerated evaporation, which contributes to foundation settling in dry weather and heaving when suddenly wetted. If grass will not grow in a particular area, a good way to maintain moisture is to turn them into gardens heavily mulched and kept watered.
The homeowner must pay special attention to anything saturating the soil in an uneven manner. Of special concern are leaky pools and plumbing. In the event the water bill goes up suddenly without any apparent reason you should check for a plumbing leak. Toilets running on can cost you a lot due to water prices (or electricity and wear and tear on a water well). Leaky hose bibs next to the foundation can result in excess foundation movement.
The introduction of water to expansive soils can cause significant subsoil movements. The introduction of water to sandy soils can result in reduction in soil bearing capacity and subsequent settlement.
The homeowner should also be conscious of water coming from air conditioning drain lines. The amount of the condensate water from the air conditioning drain lines can be significant and can result in localized swelling in the soils, resulting in foundation distress.
That’s just another way you can prevent foundation failure. Learn more in our related article Prevent Foundation Failure With Maintenance.
