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Foundations and Water
Expansive soils act like a sponge. As they absorb water, they
swell and as they lose water they shrink. Soils tend to dry out (and
shrink) during the summer and to absorb water (and swell) during
the winter and spring.
As the soil under a house shrinks and swells with the seasons,
the house and foundation will move up and down. As long as the
foundation movement is not great enough to damage the house and/or
foundation, it is not a problem. If the up and down movement of a
foundation always returns the foundation to its original level
position, then damage to the house and foundation may appear and
disappear on a regular basis as the seasons change.
If a homeowner wishes to stop seasonal house and foundation
damage, the first course of action should be to follow a
controlled watering program. By keeping the moisture content of
the soil under the foundation constant, foundation movement can
often be stopped. This is to assist the homeowner in performing a
simple foundation preventive maintenance program.
The goal of a foundation watering program is to maintain a
constant level of moisture in the soil under the house and
foundation. The best way to water a
foundation is to install a buried foundation watering system. If
you do not want to go to the expense of installing a buried
watering system, soaker hoses will provide you with many of the
same benefits. The best way to use a soaker hose
is to bury a soaker hose three inches deep, one foot from the
edge of your foundation. Placing the hose a short distance from
the foundation allows the water to soak into the soil evenly.
The hose should not be placed
against the foundation. When soil has dried and
cracked, water can travel along the cracks for several feet in
all directions. If the soil around your foundation is dried and
cracked, then water placed next to the foundation will run
through the cracks and accumulate at the bottom of the grade beam
(the thick portion of the foundation that is under the exterior
walls). In some cases, an accumulation of water in the soil at
the base of a foundation can cause the soil to loose some of its
load bearing capacity. If the soil loses enough load bearing
capacity, the house will sink into the ground.
Obviously, it is necessary to water more during hot, dry weather
and less during cold, damp weather. The
amount of water required to keep a foundation stable during the
summer can be surprisingly large. A single
large tree can remove as much as 150 gallons of water, or almost
20 cubic feet of water, from the soil each day. Shrubs and other
plants can also remove large quantities of water. During
persistent hot dry weather, it may be necessary to water a
foundation daily. Watering should supply enough water to keep the
moisture content in the soil under the foundation constant. If the
amount of water applied is only enough to keep the surface damp,
the watering program will not work.
Obviously, the homeowner is the only one who can weight the
benefits of controlling foundation movement versus the increased
size of the water bill.
The goal of foundation watering
is to keep the water content of the soil under your foundation as
constant as possible. Since you can’t keep
out the rain, the thing to do is keep the soils reasonably damp
during dry periods. To be successful, a watering program must
keep the soil damp down to a depth of 4 or 5 feet. The more trees
and large shrubs that you have, the harder this is to do. Why,
because big plants have big thirsts. The best way to water your
foundation is with a specially designed foundation watering
system. These systems are made of soaker hoses that are buried in
the ground around the perimeter of your foundation. To provide
even watering and to offset the pressure drops that occur in
soaker hoses, a separate water line is run to each section of
soaker hose. The soaker hoses will extend no more than 20 feet
away from the connections to the water lines. A typical home will
have a minimum of 4 zones, each with its own water line and
control valve. For an average home, it costs from $3,000 to $4,000
to install a foundation watering system. For a few dollars in
hoses and valves (and some hard work), homeowners can build their
own systems. The diagram at the end of this section shows how to
build a simple watering system out of common parts from the
hardware store. When watering, remember that too much water is as
bad as too little water. If you do not have timers on your hoses,
make sure that you turn them off when you are finished watering.
There is no simple way to determine how much and how often to
water. You must use your judgement. The hotter, drier, windier,
and sunnier it is, the more you need to water. The cooler,
wetter, and cloudier it is, the less you need to water. How wet
the surface is, is not a good measure of how your watering
program is working. It is possible for the surface to be soaked
while the ground a foot deep is relatively dry. One way to check
your soils, if you have clay soils, is to use a plumber’s
probe. A Plumber’s probe is a 4 or 5 foot long fiberglass
pole with a "T" handle on the end. If your soils are
too wet, then the pole can be pushed down into the soil with
little or no effort. When the soils are wet, but not too wet, you
should be able to push the probe 3 to 4 feet by leaning heavily
in the handle. If you can’t push the probe into the ground
without banging on it, the soils are probably too dry. This test
will not work well in sandy or rocky soils. The sand or rock can
keep a probe from slipping into the ground even if the water
content is high. Do not use a metal pole to probe the soils. If
you hit a buried electrical line with a metal pole, you could be
electrocuted.
1 Buy brass splitter valves. They last Longer.
2 Bury the soaker hoses 3 inches deep and 6 inches from the
house.
3 You can operate the soaker hoses individually or in any
combination,
depending on how you open or close the splitter valves.