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Making a Home for Special Needs Children
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The Right Foundation Turned a Rugged Plot in...
by Dr. Oneida Cramer
Foundation failure can strike a home at any time?even a new house under construction, according to Alan Ardoin, co-owner of Ace Foundation, which has been repairing foundations since 1956. The leading cause of such foundation problems is the heavy clay content of the soil in this area.
?The triggering element to make soil unstable is the presence or absence of water,? Ardoin said. ?Water causes shrinking and swelling?when soil gets wet, it swells up, and when it dries, it shrinks and pulls down. And this movement creates a powerful force like a slow motion earth quake.? Builders try to predict the shrink/swell potential of soil by taking soil tests to determine the type of clay and hence the foundation design that should stand up to that particular soil type.
?Still, all houses are moving,? Ardoin said. Stabilizing that movement are primarily two basic types of foundation structures?concrete slab or pier and beam. Much older homes have the pier and beam foundations, where just the perimeter beam connects with the grade and crawl space lies underneath the rest of the floor. Newer homes almost always have slab foundations?slab on grade?meaning the whole house is sitting on total concrete, which is on the ground without piers, unless the homeowner requests custom piers be built under the slab. Once a foundation (slab or pier and beam) forms a crack, the repairs often include the placement of piers under the existing foundation either around the perimeter and/or in the interior. And today there are primarily two types of piers in use.
?Another name for concrete piers is friction piers,? Ardoin said. The words, friction piers, tells you that the pier gets its ability to stabilize and hold the house from the skin friction of the dirt around the pier, which, in turn, holds the pier in place. The common practice, for many years, was to push concrete piers measuring 12 inches wide down into the soil about 3 feet deep. Because foundation problems continued to exist, the piers were dug deeper and deeper into the soil down 9 feet to 12 and 15 feet, even deeper.
?A good pier, in my opinion, should be a 12-inch diameter and be at least 12 feet deep,? Ardoin said. The deeper piers seemingly reach a depth, where the soil ceases to be impacted by seasonal changes in rainfall, past what is called the active zone. The theory goes that below the active zone, the soil won?t fluctuate and move: so, in turn, the piers won?t move.
Even the bigger and deeper friction piers continued to be plagued with problems, according to Ardoin. So manufacturers have also taken another direction by developing smaller point-bearing piers or steel piers that do not depend on the dirt around them for support. When using steel piers, foundation companies will drive down sections of piers with strong hydraulic push ramps. A typical residential steel pier measures only about 2 and 7/8th inches in diameter. But it is pushed down though the layers of active clay soil until it reaches a strata at maybe 30-40-50-70 feet deep, where ever the resistance measures two times more than the weight that that house will put on it, in other words, a substratum that has the capacity to hold this house.
?We do both. We drill poured concrete piers and we do the steel piers,? Ardoin said. ?And we?ve got years of comparison of the two. Hands down, long-term stability has been with the steel pier. And the reason we can conclude is that it (steel pier) doesn?t depend on the different layers of clay for support.?
?The ideal house, if you dug your trenches where you?re going to pour your beam, is right on rock?that?s ideal,? Ardoin said. But houses in the area of Lake Ray Hubbard need to push 70 feet before hitting anything like rock; in DeSota or Duncanville, rock can be found as little as five feet down. Older developed communities, such as Dallas and Park Cities, tend to be on areas of shallow rock-like strata, but not always, and not predictably as each site can vary from its neighbor. Today, older pier and beam homes are raised and replaced with new homes mostly on concrete slab foundations although some custom homebuilders are automatically adding concrete piers, according Ardoin.
?There?s one thing that I would require if I were buying a house,? Ardoin said. ?No realtor requires it, the state doesn?t require it, and nobody does. But I would want you to provide me with a current (1 to 3 month old) leak test from a plumber. I would want a report from a plumber to let me know there are no fresh water leaks and no sewer line leaks because those leaks cause a lot of problems, foundation-wise.?
?Water is the triggering element in soil moving, and there are two sources that water can come from?Mother Nature and plumbing,? Ardoin said. ?We can?t test Mother Nature, but we can test plumbing.?
Natural evaporation and plants take up much of the water dispensed from sprinkling systems in the yard, according to Ardoin. And sprinklers don?t use as much water as a leak can dump under a house. But under a foundation, excess water is trapped and sometimes will cause earth to heave up like a camel back and drive walls up into the ceiling. Outside the house, pooling of water, especially in rainy times, can lead to water-clogged soil that also acts like a natural hydraulic jacking up of the area, according to Ardoin. To avoid this problem, homeowners should check that all water around the house is gone within 15 minutes after a heavy downpour.
Landscaping helps to drain groundwater away from home foundations although tree roots may add to potential foundation problems, especially if the trees are located close to the house.
?If these big trees are closer than half the distance of their mature height, a lot of their roots go up under the foundation?getting the water from there,? Ardoin said. If they?ve been there a long time and haven?t caused a problem, they may never cause a problem. But trees can also send feeder roots into sewer lines, especially old sewer lines. To prevent such problems, homeowners should consider planting new seedling trees at least the recommended minimum distance from the house, or, if the lot is too small to allow this, they should add root barriers as they plant the trees.
Locating sprinkler heads around the house so that watering the foliage also waters the soil around the foundation helps maintain an even content of moisture in the soil, especially in summer.
?In my view, the primary benefit would be to control the movement of your foundation,? Ardoin said. ?The secondary benefit would be to get pretty grass.?
Dr. Oneida Cramer
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