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Building Foundations

Building Foundations

The most important part of any building are its foundations. The foundations provide the connection between the building and the ground. More importantly they provide a way of protecting the building from any weaknesses or variations in the strength or stability of the land. Here we look at basic approaches to foundation design.

Building Foundations in Britain

The British seem to have a particular preoccupation with foundations.

It must go back to a deeply ingrained sense of insecurity combined with a lot of experience building castles. Brits like to build on rock, good solid rock. If they can’t find rock panic sets in. They dig and dig until they come to something solid, usually clay, and then build on that. Throughout a British childhood there are endless stories about things that disappear in bogs never to be seen again or treacherous mires that can suck you down in seconds. Every British schoolboy knows exactly what to do when you are caught in sinking sands. You are brought up believing there are sinking sands on every street corner.

Foundations in Australia

Western Aussies on the other hand must have spent too much time on the beach. When they build a house they put down a bed of sand, cast a slab of reinforced concrete and build on that.

Foundation In Other Countries

In Bali, on yet another hand, people haven’t had such experiences with foundations, it isn’t something they have had much call for. There aren’t many castles around, they don’t go lying on the beach and, judging from the photos, cantilevered undergarments are a fairly recent introduction here.

When it comes to buildings, traditional Balinese houses are much lighter than modern concrete houses. They tend to be single story, usually have several separate buildings in a compound and more often than not have wooden frames. These buildings do not require strong foundations.

But times are a’ changing and Bali is now full of people who wish to build replicas of the brick palaces they have seen in dreary soap operas or perhaps are influenced by new arrivals building their dream home based on European designs.

Beware, while there are many highly qualified engineers and contractors around there are a number of contractors and builders in Bali who have little knowledge or experience of the civil engineering principles involved. If you have a look around it is surprising how often you will see buildings start with fairly light foundations only to have ton after ton of concrete added on top. It is common to see houses that have been built on top of relatively flimsy concrete block boundary walls?

These issues become far more serious when building on sloping sites of mud and clay. A recent story from Lombok tells of a couple building their dream home high on a ridge, fortunately the large retaining wall for the site collapsed before the contractor managed to get the house built.

Causes of Earth Movement

Landslides are a major problem throughout Indonesia and great care should be taken when building in places such as Ubud where sloping tiered land may be eroded, undercut or become waterlogged after extensive rain. Landslides have a tendency to move in rather large chunks I’m afraid.

In Bali land movement other than landslides can be expected to be much less severe and is usually the result of three circumstances:

  1. Poorly compacted fill of the building site
  2. Building on old paddy fields where there is a thick layer of mud which has a tendency to expand and contract between the wet and dry seasons.
  3. Earthquakes

Earthquakes we have discussed before ("When the earth moves") so we’ll move on.

Building of former rice fields needs special attention

In much of Bali new buildings are being built on former paddy fields. To prepare the land paddy fields are filled with a layer of white coral stone usually about 1 metre thick and the building is built on this. The fill may not be compacted well and may subside if the house being built is particularly large (many are these days). More usually problems arise from expansion and contraction of the mud in the paddy. The mud in paddy fields has been worked so it will hold as much moisture as possible. As it dries out in the dry season it contracts substantially only to expand again in the next wet - not good under a house.

Steps to make sure you have a good building foundation

Take care of yourself and consider the following:

Firstly it is important to make sure the land is stable. If it has been filled it should be properly compacted. If the land was paddy fields it is a good idea to have the mud removed before filling the site.

Secondly make sure the foundation is strong. It should be properly designed by a technically competent person and it should be closely supervised during construction to make sure the design specification is followed. Concrete should have a sufficiently high cement content, reinforcing steel should be the diameter specified by the engineer. Take note that local contractors will often save money by reducing the size of reinforcing steel or the cement content in concrete to save a bit of money. If the foundation is too weak it will be very difficult to repair later on.

Thirdly make sure the building has a well designed integral structure so that the building behaves as a single unit. If the earth moves the house will move with it.

Lastly consider building a house that is not designed to withstand a Norman siege, it is probably also a good idea to avoid falling out with anyone called Joshua.

Copyright © Phil Wilson February 2008
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