How can you run your home freely like a sailing ship for best thermal performance in the Australian climate? An earth home could be the answer.

The analogy of a ship is apt, because as with sailing there is no engine, or in the case of and earth home, no air conditioner.

My own earth home is not conditioned; it is naturally conditioned through mass-linked ventilation so the whole operation is passive, silent and free and allows for passive cooling comfort all summer.

On a sailing boat you work the rudder and sails to travel about freely. You run, reach or work to achieve this. It's impossible to say you will achieve a set distance, speed or time of arrival or departure, but sailing is a healthy, rewarding, exciting experience and on average it works very well.

At home, my expectation is for adaptive comfort according to time of day and time of year. I don’t expect set temperatures and I don’t believe it is healthy, wise, or ecologically sound to live in air conditioning, especially with a coal-fire powered grid supplying the energy. What I prefer is predictability, stability, moderation of temperature and humidity, and above all else, healthy and refreshing fresh air along with zero cooling costs.

Explorers, traders and travellers have been traversing the world’s oceans in sailing vessels freely for thousands of years and adventurers still do. A return to sail is constantly discussed and experimented with as a viable option for when the cheap fossil fuel ride ends. Modern technology recently allowed a Frenchman to achieve solo circumnavigation in a record breaking 49 days.

Sailing my home is more like sailing a large ship of reasonable displacement rather than sailing a small dinghy - more like plying a trade route in the once record-breaking clipper the Cutty Sark than darting about on Sydney Harbour racing an 18-footer or even racing to Hobart in boats stripped of weight without thought of comfort.

Is sailing just harking back to a bygone era or is it a legitimate and worthwhile modern day pursuit? Interestingly, some architects, engineers, building biologists and building simulation modelling experts are promoting a modern return to older ways of building design and management in the interest of both energy efficiency and indoor air quality. Just take a look into work done on bioclimatic design, adaptive comfort, natural conditioning, appropriate climate responsive design, mass-linked ventilation, or fabric energy storage (FES).

Clever vernacular traditional architecture has achieved both energy efficiency and air quality for centuries. If we can’t achieve it today given the knowledge and technology at our disposal, we are not trying or applying our minds properly.

Having 200 tonnes of FES at home offers me tremendous thermal inertia, resistance and capacitance - the momentum and stability that displacement and keels offer large sailing ships. I have a massive keel. This facilitates smooth operation in light, heavy or fluctuating conditions and ease of operation.

My windows and doors are like the sails. Like operating the sheets of a sailing boat, I need to sail my home by opening and closing windows and doors. The rudder is my planned ventilation logic informed by smart phone weather projections and indoor thermometers. I have a reasonably reliable seven-day forecast and current indoor conditions.

Modern technology makes my planning very simple and I use this information to my advantage. I set two to three day ventilation logic plans. The thermal mass or fabric energy storage in the building is sufficient for more than balancing out diurnal or night/day fluctuations. From experience, I have two to three days' reserve so if I see hot weather on the way, I bank as much cold night air as is possible into the FES.

It really is very simple. My home is easier to operate than a small sailing dinghy. I am not constantly working on the rudder and sail sheets to find small competitive advantage or to constantly maintain balance. I set up the home for a season and most of this is automatic through appropriate climate design.

At this latitude, 200 kilometres south of Sydney, the sun angle changes from 34 degrees in winter to 78 degrees in summer. Orientation and appropriate climate responsive design minimises solar gain during summer. Deciduous vines on the northeast, north and northwest automatically flourish to help reduce heat gain in summer and drop leaves to maximise solar gain in winter. The only seasonal adjustments to the building I make are to open the clearstory ventilation for summer and to place shades over two large skylights.

The older style double hung timber windows allow a good amount of useful leakage and I open southern toilet, bathroom and laundry windows a little to allow more ventilation through the cooler side all day dependent on weather conditions. This allows my minimum one to two air changes per hour necessary for health and amenity and stops any buildup of heat at ceilings through venting off more buoyant hot air. Then windows are mostly set just twice a day after consulting weather predictions and thermometers.

I usually check the weather over breakfast and set windows and or doors just before heading to work. This usually means closing down to minimum summer settings mentioned earlier with minor tweaks. At night, mostly around sunset, after work again consulting my weather app, the windows are usually set fully open. Sometimes I’ll wait for a late southerly change and on rare occasions they remain closed. This is a five-minute job and my simple twice-daily routine is simple.

Even though nighttime temperatures may drop below what is perceived to be cool by many, it is essential in mass-linked ventilated buildings that nighttime purging takes place in hot weather. Cold air when introduced inside is moderated by the warm radiant surfaces of the massive walls – mass-linked ventilation in practice. It is important that occupants realise this and thermal assessments model this.

The continuous though controlled use of ventilation is critical in the operational ventilation logic for thermal efficiency in mass-linked naturally conditioned buildings. Remember that, as with sailing, we are maximising freely available gains in naturally conditioned buildings not minimising losses.

So what ventilation strategy is used in heatwave conditions? When sailing into very extreme conditions it means you have to batten the hatches, drop the sails, set a sea anchor and ride out the storm. At home, you should perhaps minimise top clearstory ventilation to slow stack ventilation and keep all other windows almost closed, sometimes, both day and night relying on leakage around windows and doors for minimum air changes.

Recently the inside temperature at home peaked at 26 degrees Celsius several times in response to conditions where two to three days temperatures in the high 30s with high humidity prevailed. Outside nighttime temperatures in the high 20s were the same or higher than inside temperature, so there was no point in purging. After returning to mild summer conditions, I opened up to full ventilation.

Pedestal or ceiling fans could provide relief during heatwaves, but they seem unnecessary each time the heatwave passes.  Fans increase comfort by removing the insulating still air layer from our bodies and increasing latent heat of evaporation from moist skin. With an indoor temperature of 26 and fans, I would have sensed comfort of around 23 - very acceptable given external conditions and my choice of clothing and preference for fresh air.

Fans consume as little as 70 watts, whereas a small air conditioner consumes 2,200 watts. A fan can be likened to a small auxiliary motor on a sailing yacht. It consumes very little and is there for infrequent use. An air conditioner is more like the much larger engine of a motor launch. Once you opt for a motor launch or a conditioned home you are up for serious running costs. My home is more ruggedly built than expensive high tech racing gear in sailing yachts.

A different logic is necessary for thermal efficiency in well-sealed and well-insulated conditioned buildings. When external conditions are not more favourable than internal conditions, a conditioned building must remain tightly closed for efficiency because it stores nothing but conditioned air. If these buildings were simply to maintain adequate minimum air changes, they lose up to 40 per cent efficiency.

Some are arguing for pressure testing to ensure absolutely no losses, but this is an unhealthy, dangerous and pointless endeavour unless heat exchangers are also mandated for introducing and maintaining fresh air. Conventional lightweight sealed and insulated 6-star homes will always fail to match space heating and cooling predictions when continuously and adequately ventilated. A conditioned home won’t sail properly because its not designed to sail freely more to motor along as efficiently as possible.

In any heavy thermal mass building, earth walled or cavity brick (full brick), you will be able to operate it more successfully, though appropriate design for climate is essential. Employing passive solar principles in design and careful ventilation improves comfort and efficiency though thermal mass or FES is as vital in natural conditioning as a battery bank in any stand-alone PV solar power solution, as natural conditions aren’t always favourable.

Consider the difference between a skiff and a jet ski. A skiff needs a mast, a set of sails, a centreboard, and the tiller needs to be worked with a strategy. A jet ski needs a streamlined hull and an efficient engine matched to propulsion and has none of the features of a sailing boat. Mast, sails and keel without purpose are simply a drag. Just as you can’t design a sailing boat to operate efficiently as a motor launch and vice versa their design can’t be judged or modelled in the same way for predicted performance. There are yardsticks for measuring different classes of yachts and yardsticks for measuring jet skis, motorboats and launches.

This may seem obvious but in the case of predictions of energy efficiency of Australian homes, the same measuring stick is used for naturally conditioned and conditioned buildings. The same ventilation logic and the same comfort settings are used and minimum adequate constant ventilation isn’t required in modelling.

There needs to be serious consideration given to modelling conditioned and naturally conditioned buildings to see them differently and more fairly. A sailing ship will always be more energy efficient than a motor launch, though not if it is required to forego use of sails and rely on the small outboard motor in sea trials. A sealed and insulated conditioned building will always do well in predictions that don’t call for constant minimum air changes and then perform much worse in real life when occupants demand fresh air for health and safety.

At the end of the day, the most important consideration with regard to energy efficiency is how to reduce carbon dioxide emissions. The measure or metric used for evaluating building performance needs to be the common carbon metric (or carbon dioxide emissions per person per year) and not MJ/m2. The carbon intensity of the energy source is paramount.

A motor launch would win the Sydney to Hoard Yacht Race but at what cost in terms of fuel? And where is the challenge, the sense or sport or fair play, the sense of pure adventure in matching a sailboat against a motorboat? My 25-year old mudbrick home is carbon neutral in heating and cooling and rates a miserable 3.1 Stars, not 10 Stars in NatHERS predictions. In actual performance measured by other tools and benchmarks, it is better than zero carbon. Does this make sense?

Design for climate, operate your home for thermal performance and healthy indoor conditions and expect comfort conditions that are appropriate to climate, time of day, time of year, prevailing weather and choice of clothing. Why not exercise your intelligence, nourish your soul, encourage your health, work with the planet and do your wallet a huge favour?

  • Hi Peter
    I love the sailboat analogy..the more earth covering, the bigger the boat in terms of steering it!
    I have designed an earth covered home, built in 1984 in the Hunter Valley in NSW that has yet to use any energy to date as far as I know! Certainly while my original clients were in the home that was the case- (it has since been sold and I don't know the new owners). Glad to see the concept is getting broader acceptance- even if it is more often in 'green roof' context. My own E/C house in Baulkham Hills (sold in 2001) was a wonderful house to live quiet and comfortable and the feeling of safety from bushfires (with insulated window roller shutters) was unparalleled.

  • Thanks David. I also respect the concept of earth covered buildings. I stayed in an underground hotel in Coober Pedy and the comfort provided through natural ventilation in such a harsh environment was remarkable. I read a paper recently regarding designing for desert climates and thickening earth walls was more beneficial than adding insulation. Not sure if E/C houses work for all sites easily or practically. I guess earth buildings are similar though easier to accommodate on most sites. What concerns me is that an entire generation of designers, architects, builders and certifies may believe that energy efficiency equals an insulated sealed up box with an air conditioner. The concept of appropriate climate responsive design is underdeveloped and current policy settings discourage it.