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Don visited a classic Australian housing estate to look at some very serious drainage problems caused by the cut and fill method of construction, which is commonly used these days to build houses on sloping land.
Cut and fill is when builders cut into a hillside or slope, remove all the material from that area and then use it as fill. They then lay a concrete slab to build the house on which sits half on a filled area and half on an area below ground level. They end up with a cliff face or retaining wall right next to the house. This is a recipe for disaster, because many houses built on cut and fill sites have inadequate protection against flooding during heavy rain. This problem was evident on the day when we filmed our segment. It was raining heavily, and on one cut and fill site the area between the concrete slab and the slope was completely underwater.
Builders say that putting a concrete slab on a cut and fill site is cheap, and it is until you factor in extra costs to solve the drainage problems that occur after the builder has long gone. Putting in drainage after completion of the home is very expensive. Often there is no access for machinery to the retaining wall or the back of the house. Excavation work has to be done by hand, sometimes requiring concrete or paving to be lifted and gardens to be disturbed. The owners of the house that we looked at had paid an additional $3,000 to put in drains, on top of the $22,000 they had originally paid to construct a Besser Block retaining wall. Water was still pooling in the garden beds and cascading down the wall, so there was more remedial work to be done. Unfortunately they had no alternative to doing a cut and fill as their local council building regulations severely limited their options. In an effort to create uniformity homes were not allowed to be significantly higher than each other. New home builders had to do a cut and fill to meet the bylaws, leaving them with the same perpetual drainage problems that all of their neighbours face. Clearly local councils need to re-think their regulations.
There are many alternatives to the cut and fill operation. In the past when houses were built on a slight slope, the house was built on top of the land with small piers at one end of the block. This often provides a very useful area under the house to use for tools or storage. Normally these sort of buildings have a wooden floor, or the more expensive option is a raised concrete floor. Some people brick around the perimeter of the house, fill it with sand and put a concrete floor on top of that.
Don looked at another solution to the problem of building a house on a sloping block of land. Instead of a cut and fill operation, the builders of this particular house just brought in fill. They then built a terraced retaining wall of Allen Block, an excellent alternative to treated pine which rots away in time. However, using so much fill means that there is a high chance of movement which in this case is already happening even though it is brand new. Although this is an interesting solution to the problem, we don't recommended it.
The drainage and other problems that a cut and fill operation create are almost impossible to solve, and you'll probably have to deal with them for as long as you live in your house. So if you're building a new house, avoid the cut and fill if possible.
Copyright CTC Productions 2000