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Subsidence is the downward movement of
foundations due to failing ground strata. Often this is noticeable in brick
or stone built houses when cracks or bulges appear in the walls as a result
of the subsidence. |
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Reasons
for Subsidence
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Failing drainage pipes.
Leaking drainage pipes can cause foundations to drop by softening the
ground under the foundations or by washing the ground away. This can
particularly affect a Victorian or an older property where the drainage
has reached, or is fast approaching the end of its life.
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Trees.
Trees absorb huge quantities of water from the ground surrounding them. In
some clay soils this can dehydrate soils and cause them to shrink,
resulting in subsidence. However it is only highly shrinkable clay soils
where this characteristic causes significant problems.
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Cracks
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Not all cracks in brick or
stone walls indicate subsidence. They often occur in masonry construction
due to causes other than movement of the foundations. Typical of this are
cracks around or between the openings for windows and doors. These are often
the result of temperature changes in the wall through the year. This creates
thermal stresses in the masonry and results in cracks appearing around weak
points such as windows and doors. |
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Settlement
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Settlement is similar to
subsidence in that it is the downward movement of the foundations, but it is
a short term effect. Settlement can occur when an extension is constructed
onto an existing building. As the ground under the foundations of the
extension take the load from the extension, there is some compaction of the
soil resulting in slight movement. This can cause cracks to appear in the
masonry walls, particularly where the extension abuts the original building.
However the movement normally comes to a halt and other than repairing the
cracks, no repairs are needed. |
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What to do
Generally if cracks appear in the walls of a building the first action is to
monitor them to see if they change (either get bigger or smaller) or stay
fairly constant. If they get bigger over the course of say a few weeks to a
year, then contact your building insurer. If the building is suffering
subsidence it is your insurers who you will want to pay for any repairs, and
they will want to stop the subsidence as soon as possible to keep the costs
of repairs to a minimum. The Insurers will usually send out a loss adjuster
to investigate, but they are not structural experts and will probably ask
you to obtain a structural engineers report. |
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