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Home >> Articles >> Behold, the overwhelming tree
 From Kansas Senior Press Service - July 8, 2008By Don Carter, Structural Engineer We live in a neighborhood where most trees are still pretty small and none are taller than the roof ridges. My wife laments this, because she loves stately trees and it is generally held that mature trees increase property values and cut summer energy costs. Consider this: A city lot with 30 percent plant cover provides the equivalent cooling necessary to air-condition two moderately sized houses 12 hours a day in the summer. So, who wouldn’t want trees? Granted, they have a down side. More often than not, amateur tree planters start with saplings, which they plant near the house because proportionally they look right there. Years pass and the saplings became enormous trees with long branches and formidable outreach. Trees with long arms influence your home’s foundation in several ways, none of which are good. Let’s visit the fundamentals: 1. Your house sits atop ground that never sees the light. Land adjacent to the foundation gets baked in the August sun, saturated in spring rains, and frozen in the dead of winter. But the ground covered by your house is sheltered from these elements and stays in a fairly steady state. This creates something known as “moisture bulb,” shown in the sketch. If ground moisture stays relatively constant, the house is on a stable platform and movement is minimal. 2. Trees are pretty much symmetrical. The canopy above ground is a mirror image of the root network below; thus, when branches overhang the gutter, it’s a safe bet that roots are under the foundation. As August grasses go dormant and expose more and more earth, ground water cooks off as vapor and the tree depends more and more on water from the moisture bulb. Water content beneath the house diminishes, clay soil shrinks, and the foundation above settles and then cracks. 3. In a second circumstance, a mature tree’s root system becomes so significant that it tries to shove the basement wall out of its way. It may not move the wall, but it easily causes the wall to lean, split, or leak. 4. Finally, in older homes with clay tile or cast-iron sewer lines, trees find the weak spots and send a root invasion to draw water from there. This leads to sewer failure. 
SolutionsFirst, the obvious: It will do no good to cut the branches back, because the root system is already in place. Second, you could cut down the tree, but that eliminates energy and the aesthetic attributes noted above. Third, you can provide the trees a water supply all summer. My partner and I have looked at more than 4,000 houses in the metro area, and it’s remarkable how few houses with lawn irrigation systems have foundation distress. Irrigation is typically set to begin in June and provide two or three sprinklings a week through September. This keeps the grass and turf thick, which protects the soil from the sun’s rays, and spring rains stay in the ground instead of cooking off. Irrigation is not about pretty grass, although that’s a nice side benefit - it’s about keeping moisture in the ground for all of the many benefits. Don Carter is a licensed structural engineer and managing general partner of Foundation Engineering Specialists LLC, a company specializing in residential design and assessments.  |
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