Would You Buy This House? Part 1: Energy

Sustainability at 10 Arawa Place

The exceptional level of sustainability of this property can be explained through exemplary levels of energy efficiency, long-term durability of products, and the high productivity of fruits, veges and fowl. The entire property has been designed and managed to be low-input and high performance.

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Part 1: Energy Efficiency

10 Arawa Place has been redesigned and renovated as a passive solar home. Between April and August, morning sunlight reaches deep into the structure, bringing warmth inside early in the day when the temperature is lowest.

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An abundance of glazing on the northeast and northwest sides ensure that free sunlight energy heats the northern parts of the home on most winter days to 20 – 25 degrees. Screen shot 2014-09-06 at 8.01.59 AM

Throughout the day some of the sunlight energy is absorbed within thermal mass, ensuring that the interior does not overheat while storing the excess warmth for overnight when it is released into the home. Beyond the mass already in the structure, we added approximately one thousand kilograms of thermal mass that receives direct winter sunlight from sunrise to sunset through three large windows and the French doors. Screen shot 2014-09-06 at 8.00.21 AM

This extra thermal mass is essentially invisible because it takes the form of an extra layer of Gib on the walls, a cast iron claw foot bathtub, and a multi-fuel cooker with brick surround. When the sun is not shining, the multi-fuel stove easily heats the northern part of the home to 20 degrees or above on a few sticks of wood, with the added benefit of cooking and baking.

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Two-thirds of the home is easily heated by this combination of sunshine and a small amount of firewood. (The southern bedrooms are kept cooler as is common in most Kiwi homes.) A super-insulated building envelope ensures that much of the heat remains in the structure overnight.

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The walls in the northern parts of the villa are insulated to R-2.8 and the ceilings are insulated to R-3.6 above the kitchen and bathroom and to approximately R-5 above the lounge and all three bedrooms. These all far exceed the building code. (The underfloor insulation is incomplete at the moment.)

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We spent two winters in the small bedroom and never used a heater. Our body warmth alone kept the room above 15 degrees all night long. Temperatures in the lounge, kitchen and bathroom could drop to 14 or maybe 13 on the rare morning with a frost. Some of this strong energy performance can be attributed to a combination of double-glazing, pelmets, and floor length lined curtains, Roman blinds and window blankets. This combination of window treatments performs to a level of triple-glazing or better. Screen shot 2014-09-06 at 8.02.07 AM

Other energy-efficiency measures we used in the home were Energy Star appliances, compact fluorescent light bulbs, and solar hot water. This combination meant that our power bills over the last three years ranged from $17 to $31 per month including the daily line charge. The appliances we operated were: refrigerator, freezer, oven, toaster, electric kettle, cake mixer, wizzy stick, wifi, alarm system, clocks, radios, power tools, etc. Screen shot 2014-09-06 at 8.02.16 AM

The solar hot water system is set to a winter sun angle to maximize performance when hours of sunlight are shortest. The 240-litre tank allows ample storage to bridge three winter days without sun. We placed the temperature monitor in the hall next to the bathroom so it can be easily referenced. Over three winters, we only turned on the electric boost for the hot water a handful of times for 20 to 30 minutes each.

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To be continued…


Part 2: Durability

Coloursteel Maxx roof, November, 2011.

New, low-maintenance exterior cladding, 2012.

High quality exterior paint.

Walls braced against earthquake and wind.

Sistered bearers and joists fro added strength under floor

All floors treated for borer

All new wiring, November, 2011

Capping on fences to protect end grain from rain

Wind-hardy trees to protect netting from long-term UV damage

Earthen pizza oven protected from rain and wind

Brick patio instead of wooden deck

Driftwood – durable native hardwood timber for landscaping


Part 3: Productivity

Topsoil: 6 cubic metres for garden beds, trees and top-dressing lawns.

Wind protection: double-layer of wind cloth with new treated posts.

Rainwater collection

Compost: 8-10 cubic metres.

Native plantings for privacy and wind protection.

52+ Fruit trees: 7 feijoas; 11 olives; 13 apples; 5 peaches; 3 plums; 1 apricot; 2 guavas; 4 grapevines; 2 figs; 1 banana; 1 tamarillo; 1 orange; 1 loquat; plus rhubarb, cape gooseberry, strawberries, summer and autumn raspberries,

Vegetable gardens:

Rotational grazing of ducks and chooks:




2 thoughts on “Would You Buy This House? Part 1: Energy”

  1. Sounds like an excellent spot, well done – it must be hard to leave. It would be great to hear more about adding thermal mass to the typical New Zealand wooden house. Does an extra layer of plasterboard really make a difference? Should we fill up the underfloor cavity with rubble? (Trouble is all the wiring is there.) I’m sure you have more ideas.

  2. Thanks for sharing this! I’d be interested to hear what size your rainwater harvesting tanks are and what you are using it for (drinking/washing/garden? etc), and also how those bananas are going there. Keep up the great work guys 🙂

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