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About Expansive Soils & Map of affected areas in Phoenix
Expansive soils map of Metro Phoenix

Soil Properties: Shrink/Swell Potential

A soil survey contains maps
and a description of each
major soil in the survey area.
More important, the survey
describes how soil properties
affect a wide range of rural
and urban land uses. One of
these properties, shrink/swell
potential, is of great importance
in the construction industry.

Shrink/swell potential is the
relative change in volume to
be expected with changes in
moisture content, that is, the
extent to which the soil shrinks
as it dries out or swells when
it gets wet.
Extent of shrinking and swelling
is influenced by the amount and
kind of clay in the soil.
Shrinking and swelling of soils
causes much damage to
building foundations, roads and other
A high shrink/swell potential indicates
a hazard to maintenance of structures
built in, on, or with material having this rating.
Moderate and low ratings lessen the hazard accordingly.

As you can see by the map above (click to enlarge), produced by the Az dept. of Agriculture,
Expansive soils run in pockets throughout the Metroplolitan Phoenix area. The backround picture of this page is an example of Expansive soil.


The soil in Arizona, in some parts of the state, has "clay like" tendencies. Specific areas of the state are prone to "clay like" tendencies, sometimes referred to as "EXPANSIVE SOIL". It is not unusual for a home/building in Arizona to exhibit signs of settling by evidence of cracks in walls, doorways, garage floors, patio decks, drive ways, roof tie-ins and a number of additional locations in, on and around the home/building. The

Registrar Of Contractors, sites any gap/crack in foundations or walls etc. That exceeds 3/16th of an inch in width is considered unacceptable and requires the attention of professionals to examine the cause of such cracks.

If a consumer purchases a home from resale inventory, the Buyer should always ask the Seller for a copy of the "
Commissioners Public Report" for that subdivision. If the Buyer is purchasing a new build home, then the Builder is obligated to provide a copy of the "Commissioner’s Public Report" to the Buyer prior to the Buyer signing any contracts. In any case… no site sales associate, working for the Builder nor any real estate agent should ever issue a verbal warranty or claim as to the cause or nature or origin of these physical conditions, whether visible or hidden or whether disclosed or undisclosed.

It is the responsibility of a prospective homeowner to satisfy his or her concerns by securing an independent assessment of the home/building and the structural integrity of that home/building. A licensed, bonded and insured (PE) Professional Engineer or (PEF) Professional Engineering Firm should tender such assessments, in writing to the party or parties raising such concerns.