Designing for Sustainability

Warwick Rowell, Wednesday 28 August 2013 (Notes for a house tour August 2013)

How do we define sustainable housing?

We define it as a structure that is adaptable, comfortable to live in, that will last at least 300 years with good maintenance, and that the ongoing maintenance must be as straightforward as possible. Stewart Brand makes the point that after initial construction twice the build cost will be spent on maintenance. Christopher Alexander makes the further point that mortgage interest takes up one third of the money, which frequently leads to maintenance being neglected. (see Sustainable Housing: Lessons we have learned so far for more on this, and detailed references)

Thinking about sustainability starts with meteorology, geography and physics.

What is the climate like now, and into the foreseeable future? How hot, how cold, how humid, how dry, how windy all impact on the design solutions you might consider. How much sun do you get? When? How much sun do you want?

Generally, we are on the southern end of a Mediterranean climate zone, with cold wet winters and hot dry summers. In 1990, Emeritus Professor Bert Main advised the government of the day that the most probable consequence of climate change for WA was a shift of the major climate zones up to 800 kms to the south. So tropical climates would extend to Carnarvon, the arid climates would extend south to about Busselton, and the deep southwest would be Mediterranean, and lose that misty SE cloud and rainfall off the bight. This would mean more and stronger cyclones, and much less predictable rainfalls, which would make grain farming very difficult.  (See Permaculture and Climate Change in Western Australia).

More particularly, we are 4kms from sea in two directions, and very near the top of the Naturaliste Ridge, at about 132m above sea level.

Our rainfall pattern is effected substantially by this position.

The orographic effect of clouds having to rise from sea level over such a short distance gives us about double the rainfall of Dunsborough. Nevertheless, rainfall has diminished considerably since we came here; roughly we averaged 1250mms for the first five years, 1000 for the next five, 750 for the next five, 1000 in 2012, and just over 800 so far this year.

Parenthetically, our heaviest rainfall event since 1996 was 41mm in 41 minutes, for a total for the day of 89 mms, which is why we pay so much attention to surface drainage!

Knowing our rainfall, we did some sums with respect to roof and tank area, and height of tanks.  With two tanks with a floor area of about 60 sm each, and a roof area (including one tank) of about 540 sm, we have a multiplier of 4.5:1; that is 1mm of rain puts 4.5mm into both tanks.   As the tanks are effectively 2100 mm high, this means we need 466mm of rainfall to take empty tanks to full in any one year.    So on present rainfall figures, we have a buffer of around 100%.

We still encourage water saving, and short showers, despite recycling water again, as we estimate the orchard will need about 10 litres of water for each Kg of fruit and nuts it produces, and the vegetable gardens about 20-30 litres per Kg. Using Dry Composting Toilets also saves considerable water use.  After experience on the use and maintenance of eight different types of DCT, we recommend the Rotaloo brand.  This is because they reach what we regard as the right compromise between volume for heatmass, lightness for ease of handling, and the maximum separation of use and handling operations; some distance, and maybe as much as three years! We see DCTs as very healthy, because the nasty anaerobic bugs in our guts are exposed as soon as possible (rather than transported and then treated in water), and there are huge breaks in any possible cycle of contamination.

To further reduce water needs, in summer we will shade large areas of the kitchen garden, and use dense planting, heavy mulches, and lots of ground covers to protect the orchard area. Straw mulch at least 200mm deep is needed to protect soil from wind and sun here in summer.

Very heavy rainfall can create huge problems.

Many factors contributing to sustainability are invisible when the building is finished. Despite the fact that we are only one metre below the crest of the hill, we have three different forms of drainage to protect our building; rocks block surface flows.

The surfaces inside the rocks have been carefully contoured and heavily planted, the driveway slopes away from the house, the clay under the pad has outwards slopes to all sides, and we have grit and pipe sub-surface drains – lots of redundancy.  We were generous with the excavations, and the volume of sand we brought in, to have a pad that was up to 2m wider than that required, and we compacted it about 30% more than specified; 11s and 13s around the edge, rather than 9s.    (The numbers refer to how many times a weight has to be dropped a set distance for the metal rod to which it is attached to penetrate a fixed distance into the ground.)

The concrete slab is 125mm thick, rather than 100mm, the reinforcings are all larger than required, and the corners have four layers of mesh and other reinforcement.    The slab of the main house has NO through slab fittings for plumbing or wiring.   With the verandah to the west, we were forced to have through slab fittings for the new bathroom, but they are substantially reinforced, and have two separate white ant treatments.

Generally this is a windy site.

And it will hopefully remain so; see the later comment on aesthetics.  Our dominant wind directions are SE, SW, NW, and NE, in that order. Our very strong winds are mostly prefrontal NW, followed by SW, then less frequently, but with more severity, SE, then SW.  In 1997, and again in 2012, we had very strong wind events, with winds consistently above 100 kph and gusts I estimated to be around 170 – 180 kph.  (I have been sailing in gusts of 190 and 200 kph, so I have a feel for these speeds!)

The first strong wind event in 1997 made us more cautious than before, and all our structures have been built to exceed normal and cyclone specs, with our new extension being an example of our increasing caution!

The extension of the hips to the west reduces the vulnerability of the original gable wall, the gutter line is closer to the natural ground surface, and the house is further protected by the westerly ring of rocks (from both the wind itself and any flying debris).   The roof structure is very simple.  All glazing is safety glass, and particularly exposed windows will be/are screened with aluminium security door material, which would provide a further barrier to wind blown debris (and embers from a fire).

The walls timber frames are glued, and then bolted into the slab.    All wall fastenings of timber to timber are upgraded, and cross bracing is overdone.  In the main house we did the structural engineering for pine, and then built with jarrah.  The posts and beams are all oversize as well.   Look at the size of the verandah posts, and their construction!  (below right)  All the shade sail supports are independent of the house.  With extra bracing as a bonus, the main electrical wiring is contained in the heavy box frames about two metres high around the inside of the house for ease of access, visibility, and reduction of electrical risk factors.  (below left)


Cold temperatures are not of great concern here.

The heat mass of the ocean only 4 kms away in two directions keeps air temperatures mild.  As well, cold air sinks from the top of the hills down into the valleys.  The coldest we have ever experienced here is 4C.   Double glazing and strawbale bale walls and ceilings are enough, although the average 2m rock walls of our bedroom work well too: the temperature there has ranged from 17 to 27 C over the year.  We are enjoying the extra warmth from the greenhouse blinds installed on the now enclosed verandah (above); if we want to get even more heat in from there, we might put a kitchen fan high in the wall in the SE corner of the verandah.

In summer we use a semi-passive solar strategy.

We put up shade sails to keep the sun off the bedroom, dining room and kitchen windows, under the polycarbonate in the verandah, and this year over the kitchen garden.  If, despite this, the temperature inside the house creeps up during an extended hot spell, we can easily capture any cooling breeze by opening a few louvres or doors.   Bear in mind that for really effective purging of hot air, you need three times the area of opening on the leeward side as on the windward side, and at least double that – 6:1 – if the doors or windows are flyscreened.

Fire is another important concern in planning for sustainability.

Much can be done at the planning and building stage, as well as on a retrofit approach.  The most important factor after that is how carefully and realistically you plan for all eventualities.

Gillian is coordinator of the local Bushfire Ready Group, which has given an impetus to a huge amount of work on improving fire safety around the house.  

We have two sprinklers on the roof, which has a very simple structure with no places for leaf debris to accumulate, with large gutters and downpipes we can block easily.    The two water tanks are connected to two pumps, one of which is a heavy duty emergency one, with 18mm pipes to critical points.  (The batteries with nine days power stored on the least vulnerable side of the house mean we do not have to think about emergency water pumps as others might.)

Around the house we have wide swathes of bare ground, with gravel or hotmix driveways and parking areas, and large areas of mulch and ground cover.

Fire risk reduction strategies are important.

We have four two way radios that all can use, Richard our son, who lives next door, has a 700 litre tank/pump system that can easily fit onto the back of his ute.  We have identified ten different areas of possible action, and are well into the ongoing process of detailing them, estimating and testing times required, and then putting them into a matrix with available resources/and limitations on the other axis.  More details are available if you contact us.

We briefly discussed sustainability of food sources; we have a fenced and netted orchard space, a kitchen garden that is nearly enclosed with logs and wormwood, and we have kept pigeons as a meat source for over a decade.

We didn’t get to discuss the necessity for power independence in any great detail.  Some capacity to survive a power blackout is more sustainable than relying on transmission lines to distant power stations.   This means some form of generator, or batteries, and maybe solar panels.  The key factor in managing battery longevity is a simple voltmeter with indicator lights which you can see say twenty times a day as you go about your lives; then you can see how you are going.  Solar hot water, light access, LED or compact fluoros, solar ovens, haybale ovens, design for minimum consumption by efficient appliances… another large topic!

The psychological and social impact of our efforts are important.   
Much of what we do to increase sustainability ends up as invisible, but a large part is visible: Is it simple, yet with some style that makes us and our guests feel comfortable? 

A key influence on us as we design the houses we build, and help others design (via Your Building Company), is Christopher Alexander’s Pattern Language.   See more detail on this on our website: Six Questions to Answer in Evaluating your Home Book Review – Pattern Language – The Basic Concept by Christopher Alexander or contact us for more detail.  The question “Does the building fit the landscape?” is rephrased by Christopher Alexander as a Pattern, an imperative: “Repair the whole”.    That is, does what you build and grow actually make the surroundings seem more integrated, comfortable, in tune?     We love the wide open spaces here, which let us see the whole sky; the racing clouds, the gentle sunsets, the spectacular dawns.  These would be lost if we (and others) planted trees for windbreaks or just boundary markers around our properties.

Building occasionally, retrofitting more often.

Buying the right house in the right place is a hard thing to do, and this is made more difficult by considering all these different aspects of sustainability.  But it is very hard to achieve as much sustainability as you might want, unless you are building again.  For many, increasing sustainability – dealing as best we can with  cold, heat, wind, flood, fire, power, food, light, comfort  – can only come from retrofitting an existing dwelling.  To address this difficulty, the Permaculture Association of WA devoted two issues to retrofitting your house in the SW, for winter and summer.

Thanks to the Busselton Naturalists Club for joining us to explore and discuss our efforts to make a sustainable house: one that is strong, simple, flexible, comfortable, and that will provide psychic and material protection and sustenance to its occupants over many decades to come.