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Foundations
There are four types of foundation: Deep Strip, Raft,
Trenchfill and Piled. Wherever possible, establish ground
conditions by means of a survey in order to pre-determine
the foundation method best for your site. |
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Deep Strip Foundations
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Key Points |
1 |
Concrete burns the skin so always wear protective gloves
and footwear. |
2 |
Ensure the base of any foundation trench is clean, level,
dry and free of any loose material. Trench sides should
be cut square with the base. The ideal situation is
to excavate the trenches and pour the concrete the same
day. Special mixes that flow around whole channel are
available, which do away with barrowing. |
3 |
Foundations poured in winter conditions must be done
following strict guidelines and should be covered over. |
4 |
It is best to consult a weather forecast for possible
frost conditions because overnight frost can ruin concrete. |
5 |
If you decide to use a concrete pump to place concrete,
give the suppliers plenty of warning of your intention. |
6 |
Locate your nearest hire depot for urgent requirements
such a water pump in the event of flooding. |
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Deep Strip foundations are the least expensive and are
used
when ground conditions are good. A concrete strip, sometimes
reinforced with steel mesh, supports the walls. The trench
depth is variable but in most cases should be at least 1m
with a width of 600mm. The concrete should have a minimum
depth of 225mm.
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Trenchfill Foundations
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Trenchfill foundations fill the excavation,
almost to the top, with concrete. Although more expensive
than a Deep Strip foundation this method gets you out of
the ground quickly. The Trenchfill foundation is used when
soil is loose or in areas with a high water table. In areas
with heavy clay and in the presence of trees, Trenchfill
foundations may be taken deeper, to a level where the moisture
content of the subsoil is unaffected. It may also require
the provision of mesh reinforcement and the trench sides
might need to be lined on one or both sides with a compressible
material an /or a slip membrane.
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Raft Foundations
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Raft foundations are used where the ground
is inherently stable but where conditions deep below the
surface, such as mining, might lead to ground movement.
The reinforced raft is cast on top of consolidated hardcore
and is shaped at the edge to provide a step upon which both
leafs of the wall are constructed.
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Piled Foundations
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Piled foundations are used where good
bearing ground can only be found at deeper levels or where
physical restraints make other forms of foundation impossible.
A Piled foundation is usually carried out by specialist
contractors. The piles can be dug, bored or driven into
the ground. They support a concrete ringbeam or groundbeam
that spans from pile to pile, upon which the house is built.
This ringbeam can be prefabricated but if it is cast on
site it may be necessary to have reinforcement cages ready
made up to an engineer's specification. In certain situations
it may also be necessary to have compressible materials
on hand to line the underside or sides of the beam.
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Overcrowding on Site
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Bear in mind that during the course of the build a number
of items may be needed at short notice such as scaffolding,
diggers, dumpers or cranes, so ensure there is adequate
space for them. It is also a good idea, if you have room,
to position a skip on site for the gathering and regular
removal of rubbish as the build progresses.
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