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Earth Sense: Check house foundation to prevent dangerous slides

POSTED: April 19, 2014 10:20 p.m.

The March 22 mudslide in Oso, Wash., raises the question whether something like this could happen here. It’s not likely, because we don’t have the deep soil that led to the Western disaster.

But when looking at a prospective home, its foundation deserves critical examination. If a house is built on a slab, and the slab rests on clay soil (recognizable by its reddish color), trouble could be present. On sloping land, rainwater can penetrate beneath the clay and lubricate the zone where the clay meets solid bedrock. Because clay is slippery, it can then creep downhill, taking the slab and the house with it.

Look for cracks wherever concrete is visible, like the garage and all around the base of the house. Other structures are set on stacks of cinderblocks, forming a crawlspace. Recent codes in most counties require that those pilings extend down to solid rock, but older houses may have them sitting on soil.

Check whether the cinderblocks seemed to have moved any, or if they are buckling or have cracks in them. This also could indicate shifting of the foundation. If a cinderblock wall is visible around the bottom of the house, the blocks must not display evidence of separation between them. A foundation wall that’s leaning in a direction away from vertical, especially on the downhill side, could be in trouble. Bring a bubble level with you when looking at houses.

The “rim joist” is found where woodwork meets the cinderblock foundation. It should be resting squarely on the blocks, without signs of displacement. Even if you plan to hire a building inspector before purchasing, it’s a good idea to bring a strong flashlight and do a first inspection yourself. This is especially important where a water body is nearby, because changes in the water level also make the ground water table go up and down, altering the level of support underneath the house.

Like all lakes in North Georgia, Lanier is an engineered lake. This means that the lake bed and its surroundings have been altered artificially, and a high level of professionalism is needed to build a proper house foundation. Any signs of cracking, separation or sliding are a warning that expensive repairs may be needed.

Among home inspectors, qualifications may vary, so the cautious buyer will select one who is Southern Building Code or International Building Code Certified.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.


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