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21 September 2020

A Challenge to Aim for the Sun


"Building a high-performance family home resulted in behaviour change and international recognition. Tanglewood, our family home rebuild in the Eastern bays of Auckland, just achieved Petal Certification for Energy, Health & Happiness and Beauty by the ILFI under the stringent Living Building Challenge, the leading global building standard!

When asked how much the energy system cost, we answer, 'less than the cost of the driveway which doesn’t pay back anything!'

How did we do it? An energy budget was calculated from the energy use in our previous house, plus 20% extra to allow for charging a fully electric vehicle. However, the new house performed substantially better than expected in terms of comfort and energy generation. With extra thick, fully insulated walls and low-e double glazed windows in thermally broken aluminium joinery, Tanglewood only needs the central heating/cooling for a handful of hours each year. This was really surprising as Tanglewood has no thermal mass. Detailed attention to ventilation and humidity control contributed significantly.

Net Zero Energy Certification requires energy generation equivalent to 105% of the household annual energy consumption. We overshot the target by more than 100% and are stoked we did. Our solar electric panels are wired to our Tesla Powerwall battery, which reduces our demand on the grid to a minuscule 300 kWh over 20 months (a typical house uses well over 300 kWh per month). In that same time, we exported 12,000 kWh toward offsetting the energy consumed in creating the materials and fabricating the house, car and driveway.


Comfort is always key and the ceiling fans help circulate the sun’s winter warmth and provide cooling air movement in the summer. Fully screened windows and doors enable us to adjust to outdoor conditions without concerns about insects. Other elements vital to overall comfort were the Lunos energy exchange fans for controlling humidity in the ensuite and laundry by extracting moisture while maintaining the interior temperature by recycling the warmth. Shower-domes keep the moisture inside the showers and ensure bathroom mirrors only steam up when we take a bath.

Modern, efficient technology enables healthy, comfortable homes that are self-sustaining but this doesn’t happen without behaviour change. Perhaps the attitude and behaviour is more important than the technology... It became a personal challenge to avoid running out of battery and having to take power from the grid during winter. Being seasoned yachties, it was second nature to watch the weather and plan when to charge the car, do the laundry, run the dishwasher, or overheat the hot water cylinder to last a little longer than usual. Self-imposed challenges are often the most rewarding!

Every kWh saved at Tanglewood leaves water in the hydro dams for later, and if enough people rise to the challenge and aim for the sun, NZ will cope with growing power demand without more massive infrastructure projects wiping out rivers and lakes."

Written by Jon & Yoshimi Brett, Tanglewood Owners

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