The Not so Blank Slate

22 07 2008

To have a truly thermally stable house, you must have a lot of thermal mass, that is heavy material like concrete, inside the building. Thermal mass has the unique ability of soaking up heat, and storing it a long time. Just as black bitumen roads get very hot in the sun, and remain so long after sunset. Therefore I had no choice but to build on a slab, and do so across the natural slope…. not easy.

To achieve this, I had to split the house down its middle, with the two floors 1200mm apart (about 4 feet) and build 6 steps to gain access between them. This is a bit of a compromise, but then what house isn’t?

The middle photo shows the slab shortly after pouring, including the step down and the bay where the steps now reside.  To add even more thermal mass, quite a few internal walls were built of concrete blocks, and core filled with yet more concrete.  In all there are some 150 tonnes of concrete in this house, and whilst I realise there is a high environmental price to pay for such heavy material, the energy savings are so great that it will pay for itself in a matter of fifty years.  Compare that to the usual brick veneereal disasters built every day around you which have just as much embodied energy in their materials, but then require considerable air conditioning energy to maintain comfort for the house’s entire life…

Notice how the high block walls which form the ‘ends’ of the building have no windows at all?  That’s because you cannot adequately control sunlight on the East and West sides, and with a long narrow house like this, enough light is available from windows that only face South and North, North being the important side (or rather the side facing the equator to universalise the concept).

Foundations like these didn’t come cheaply, but then just look at that gorgeous view… and then consider that when we have a frost outside (it went down to -6 deg C last winter!) we were still nice and cosy with no heating at all.  And last summer when the temperature hit 43 deg C, it hardly went over 30 inside.  And I hasten to add the house is still not finished, many gaps still needing to be filled to disallow entry of hot and cold air on extreme days.

In winter the sun shines into the house all day long and heats up the thermal mass which acts as a heater overnight keeping the temperature around 20 degrees oe more until the sun comes up the next morning.

In summer. the sun never enters the house, but any heat coming in through windows is soaked up by the concrete keeping the house cool.  At night the heat is vented out the clerestory windows.

The photo at right is what it all looks like finished.


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More Blank Slate

21 07 2008

We paid just $49,000 for that land. Amazing isn’t it? Just 6 years later, the owners of the land diagonally across from us are selling, and asking $368,000! They won’t get it. Still…… just goes to show how stupid real estate has got.

The criteria was to build a state of the art energy efficient house, so efficient it would need no heating, no cooling, and run pretty well on 100% solar power. I don’t want to have to rely on a failing Matrix to supply us with our hot water and power. No way.

I know how to do this now, I retrained in the 90’s, doing a tertiary course in Renewable Energy, and since acquired accreditation as an energy rating assessor. Trouble is, the land faces West and South, and such a house has to face North. Why face North? Because that’s how you have total control over the sun, because that’s where the sun is most of the time in much of the Southern Hemisphere. Align your house on an exact E-W axis, and you can totally control when the sun enters the house through windows, or not. Yeah, I’m a control freak!

Most people think the Sun rises in the East and sets in the West. Well it does, but only twice a year, at the equinoxes, March 21, and September 21. Any other time, and the sun follows paths similar to the figures above. So when you build on an E-W axis as above, the sun never shines on the front of the house in summer, but does so all day long in winter. That is called passive solar design, and it’s great because every square metre of glass the sun shines through is equivalent to having a 1000W bar heater on. This is useful in winter but appalling in summer, at least in the warm climate where the blank slate lives. All you have to do is exclude all E and W facing windows, and you’re in business.

How do you do without windows on E and W sides? Simple. Just build a long narrow house with its long sides facing N and S, and then build into the roof openings called Clerestory Windows. These windows allow evacuation of rising hot air in summer, but when closed keep warm air in all winter long. They also light rooms all year ’round, and even allow direct sunlight into the cooler southern side of the building in winter. Free heat! What more could you want?

Well…… there is more. Watch this space.