Why many homes in 'Tornado Alley' don't have a basement - WSFA.com: News Weather and Sports for Montgomery, AL.

Why many homes in 'Tornado Alley' don't have a basement

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Soil with a high percentage of clay tends to dry out and crack, as pictured here (Photo: Activerain.com) Soil with a high percentage of clay tends to dry out and crack, as pictured here (Photo: Activerain.com)
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(FOX19) -

What? No basements in Moore, Oklahoma, located right in the heart of Tornado Alley! What are they thinking?

I have heard this many times since the town was struck by the deadly EF5 tornado on Monday.

The short answer is actually just one word: Clay.

Soil scientists talk about bentonite, illite, montmorillinite, chlorite, kaolinite and vermiculite. You may recognize the last one if you tinker with gardening.

To cut to the chase, the characteristic of clay important to the Moore, OK tornado story is that clay has an amazing capacity to expand and contract. In fact, some clays expand 30% in volume as they go from dry to saturated with water.

A basement situated in a clay soil will undergo tremendous changes in pressure. When the clay soil is very dry, it shrinks back and the basement loses support, threatening collapse.

It's common in regions with very clay-ish soils to see home owners with basements watering the clay during times of drought to keep it from shrinking away from the foundation.

When the clay soil is very wet and expands, basement foundations can be cracked, and in the worst case, loose structural integrity.

There are engineering solutions to this problem, but the cost is just too high for the average family home.

So for now, it is unusual for a home in Oklahoma's part of tornado alley to have a haven from the storm in the form of a basement.

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