Civil Engineering Reference
In-Depth Information
Thermal mass, is it for you or against you?
Our straw bale house in Heathcote has a concrete floor downstairs with slate tiles. I find
in summer that it is terrific. The floor is cool and I am sure it contributes to the low
temperatures in the house on the hottest days. However, having a cool floor in winter,
which certainly is my experience, is not so appealing. Because the floor is so cool, a direct
consequence of sitting on the ground, which is cool, the heat that we generate to heat the
room also has to heat the floor. The benefits of thermal mass are heralded as a solution to
heating and cooling, but it can work against you.
If you have a large mass of material that is cool, and you want to heat the area, the
coolness contained in that mass must be displaced with warmth. With a concrete floor
you have the added disadvantage that the earth below the concrete also represents a more
than significant mass, and it is cool. So to warm the concrete slab we are also fighting
against the temperature of the earth. The concrete will consume a huge amount of energy
to achieve a neutral temperature. Whereas a timber floor with appropriate insulation is
probably more likely to gain a neutral temperature with much less heat generation, as the
heat is contained in the cocoon of the room without the complication of having to
convert a cold mass before the room is warmed.
Soil reports
A soil report and how to get one
As briefly mentioned in Chapter 2, a soil report is required to determine the type of soil
and its capacity to carry the load of the building. The soil tester may use a machine to dig
the test holes or a simple hand-operated auger. They will do several test diggings on the
site in an attempt to establish continuity of soil on the property. On occasions one or two
of the tests may indicate stable soil while a third may indicate that the land has been
filled. It is necessary to have a soil report as this forms part of the application for a
building permit. Most engineers can arrange to have a soil report done for you.
When buying land it is a simple process to make the purchase conditional upon the
results of a soil report. The agent will probably want you to specify what test results are
acceptable, and will most likely include this detail as part of the special condition on the
contract. I will cover the various soil classifications and their definitions shortly, but I
would suggest that soil of class A, S, or M would be good. I would be hesitant about
buying a site with rock if you are on a tight budget, as the cost of rock removal can run
into thousands of dollars. A site with rock would most likely be class A.
The soil report saved the day
Some years back I was asked to do a quote on an extension to a brick veneer home in
Doncaster, Victoria. Fortunately, while it was not required in those days, we had a soil
report done. One of the tests revealed that the site had slightly reactive clay, which was
quite acceptable. The other two tests revealed that the land had been filled. Further
investigation revealed that the proposed site for the extension was on the edge of what
used to be a dam that had been filled prior to the subdivision of the land. There was over
three metres of fill in the dam. The solution was to drive piles four metres into the
