Monday, March 8, 2010

On building a house in town 2

How is our house different from a "normal" house? And how is it the same? Our design criteria were to build something low maintenance, with zero heating and cooling costs and as autonomous as possible without resorting to technologies which might not be available or easily maintained into the future. It must be comfortable and robust: able to cope with the more extreme climate which may develop over the next few years and decades. And it must be as cheap to build as possible fitting the criteria already outlined.

The obvious way to heat a house is using the sun and the house I built in the 1970's was what is called a passive solar design — the sun shone in on a tiled concrete floor in winter and heated it up, thus moderating the temperature during the night as well. I wasn't a great builder and had very tight finances, so it didn't work as well as it could have but with the mild climate at Waratah North, close to the sea, it was better than nothing and certainly better than the house I grew up in only a few miles away in Toora.

But the Waratah North house was weatherboard and had fairly skimpy insulation (none under the wooden floor) and lots of single-pane glass, plus it had no ventilation other than through opening windows. Also the sun coming in faded the furniture and any other thing it fell on, so you had to be careful what you put in the room. The glare could be hard to bear at times as well. And the room which didn't get the direct sun got mouldy and musty.

The new house has a much more sophisticated solar heating (and cooling) system. While the sun can come into one bedroom and a corner of the living room directly, most of the heating will be via a solar air heater on the roof from which air will be blown by a fan down under the concrete slab floor and through a rock pile heat store, which being fairly massive (around one hundred tonnes) will hold the heat and release it slowly up through the concrete slab. A second, separate solar heater will draw stale air from the house via a system of ducts such as you would find in large commercial buildings and before venting it outside it will pass through a heat exchanger where it will heat incoming fresh air. The house will have lots of interior thermal mass, well insulated from the outside, and double glazed windows throughout.

In summer the same solar powered air extractor will draw air up through the rock pile (which will cool the hot exterior air on very hot days). There will also be a solar hot water heater. The toilet will be a composting type so we can recycle waste into the garden and cut down on water usage and disposal. All our water will be collected from the roof of the house and carport/workshop and stored in a large 90,000 litre concrete tank which we've just had constructed. We had a similar setup at Waratah North and the water from our concrete tanks there was like champagne! The water will be pumped to a small header tank on a stand via a small solar powered electric pump — no noisy pressure pump which stops running if the power goes off leaving you with no water.

The advantage of this heating/cooling setup is I can build it and maintain it all myself. There are no microprocessors involved and the highest tech items will be some fans and an electric pump.

As for the construction of the house, it will have a series of flat roofs made of the kind of material developed for big commercial buildings using insulation glued between two metal sheets. It can span a large distance which cuts down on most of the carpentry needed for roof framing. The outside walls will be corrugated colourbond mostly, fixed to treated prefabricated stud walls and heavily insulated, with a couple of timber finished walls in the courtyard to cut down the harshness of the finish. The colourbond is low maintenance and cheap, plus a good material for our fire vulnerable site on the edge of town.

The floors will be concrete slabs for thermal mass and silence! We are planning for rammed earth interior walls for thermal mass as well.

No windows on the east or west walls and only one glazed entrance facing west in the courtyard under a roof overhang. All windows are well under eaves (we're starting to get more frequent large hailstone events). No lawn! The north facing windows (which are all on the ground floor) are protected by stone courtyard walls from any possible fire. I've got to figure out how to glaze the solar heat collector with strong enough, long lived material at a reasonable cost.

It's not a simple house at all, but hopefully by limiting the amount of plumbing and not going stupid with the kitchen (fortunately I can build all this!) we won't shoot ourselves down financially.


Geoff said...


Great house design!

There is a house project underway in Victoria that is exploring the principles of permaculture as outlined by David Holmgren via a blog which would probably make interesting reading:


questions said...

Do you honestly think you can repair a broken fan or water pump? I've tried, and failed. I've had more luck fixing electronic devices.