Expansive Soil
With significant real estate development Washington in the past 20
years, the problems caused by expansive soil have become painfully obvious. Many
people have literally lost their homes due to extensive damage and the high costs of
repair. In some cases, class action lawsuits have been brought against builders
and/or developers for failure to follow the recommendations of their soils engineers, or
for failure to properly disclose the potential risks associated with purchasing a home
built on expansive soil.
Map of Washington Showing Swell Potential of Reactive Soils
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Unit contains abundant clay having high swelling potential |
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Part of unit (generally less than 50%) consists of clay having high swelling potential |
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Unit contains abundant clay having slight to moderate swelling potential |
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Part of unit (generally less than 50%) consists of clay having slight to moderate swelling potential |
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Unit contains little or no swelling clay |
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Data insufficient to indicate clay content of unit and/or swelling potential of clay (Shown in westernmost states only) |
"Bentonite" is a term commonly used to describe expansive soil. Expansive
soils such as clay, claystone, and shale will "swell" in volume when wetted and
will shrink when dried. This volumetric expansion and contraction can cause houses
and other structures to heave, settle, and shift unevenly, resulting in damage that is
sometimes severe.
Minor damage from expansive soil movement can sometimes be repaired for less than $5,000.
However, major damage can cost $30,000 to $50,000 and occasionally up to $100,000
or more to repair!
Geotechnical engineering and structural
engineering have come a long way in the last 20 years, and specific foundation systems
have been devised to help counteract some of the problems inherent with expansive soils.
However, the risk of damage to homes can be minimized but cannot always be
eliminated.
Here are several good reasons for having your home inspected by a trained professional:
What's a homeowner to do? Educate yourself about expansive soils, of course. Here are few tips to get you started.
Read the soil conditions report.
Before you buy a new house or a lot in a new subdivision, ask to see the soil
conditions report. In the mid-80s Washington passed a consumer protection law requiring one
for all new construction.
Ask about the type of foundation.
Expansive soils require special foundations. Basically, concrete
pillars are set down onto bedrock. Then concrete beams are placed atop the piers. A thick
cardboard spacer can be placed under the beams so that if the soil heaves, the spacer will
be crushed but the floor won't move. The walls, especially in finished basements, are
separated by 2-4 inches from the concrete slab with small spikes for the same reason.
Learn about these techniques before finishing your basement.
To save money, homeowners often finish their own basements. That's fine, but if your
house if built on expansive soils, you'd better incorporate the above-mentioned
construction techniques or you'll end up with cracked basement walls or floors.
In older homes, look for wide or uneven foundation cracks.
If your home was built before the soils testing requirements of the '80s and you're
concerned about expansive soils, you probably only need to worry if you find wide (a
quarter inch or more) or uneven (one side higher than the other) cracks. Hairline cracks
are usually caused by normal settling. If you're unsure, call in a professional inspector
or soil engineer for his analysis.
Ensure proper drainage away from the house.
Expansive soil conditions are made worse when water collects around the home's
foundation. Rainfall should run off the property as fast as possible following a storm.
Rain gutters and downspouts should direct water away from the house, discharging it no
closer than 3 feet from the foundation.
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Pacific Crest Inspections is a locally owned home
inspection company providing home inspections, commercial inspection and pest
inspections in the Bellingham, Wa. area. Pacific Crest inspections is licensed
by Washington State and carries the highest certification “Certified Real Estate
Inspection” offered by the National Association of Home Inspectors (NAHI)
Pacific Crest Inspections conducts their Washington State home inspections
according to the National Association of Home Inspectors
Standards of Practice & Code of Ethics. These
professional home inspection standards provide a minimum guideline for
conducting a Bellingham, Washington home inspection. Our home inspection
standards are available for viewing under the "Consumer Information" section of
our website or ask your Washinton home inspector for a copy of the NAHI Standards
of Practice & Code of Ethics prior to your Bellingham home inspection.