Coatesville Passive Solar House in Rodney, North of Auckland, New Zealand is a series of stacking saw tooth roofs designed to capture every possible bit of sunlight during winter and naturally exhaust warm air through a series of clerestory windows during summer. The family house design is a bit like an old saw tooth shaped factory roof- but smarter! The home is 270sqm situated on a 2.5 acre property with bush and valley views.

Typically a passive solar house works on an east west axis following the seasonal sun path direction. This site has a narrow east facing flat platform located on the downward side of a hill. This meant we had to design within a restricted foot print which worked on both an east west axis, and north south axis for maximised solar gain and view. We found the saw tooth roof idea worked well with the site and seemed like the logical design direction.

The house relies on exposed insulated concrete slabs and large insulated vertical precast concrete walls for optimised passive solar gain and heating during winter time. The roof shapes and windows function as large clerestories allowing a natural stack effect to cool down the interior and naturally ventilate the bedrooms and living spaces over summer time.

The house is designed for an anticipated 5500kWhs annually or an annual energy index of 20.4kWh per/sqm, the remaining power will eventually be provided by a 6.0kW grid connected solar panel system .Internal temperatures passively peak at 24⁰ during later afternoon mid-winter, with the extreme low being 17⁰ during early morning. So far the house has thermally performed as calculated. Green technologies and features which have been incorporated into the house are an onsite tiger worm composting system that treats black and grey water, hot water is heated through a hot water heat pump (sucks heat out of the air), 54,000 litres of rainwater harvesting capacity will provide drinking water, bio-paints are used for interior finishes, above code insulation for walls and roof, long lasting low maintenance bricks for the exterior, cedar fascia boards at roof and deck edges, energy efficient appliances are standard items, and water efficient tapware are used in bathrooms and kitchen.

The combination of passive design strategies, passive solar, passive cooling, energy efficient technologies and an eventual 6kW solar panel system will render the house energy self-sufficient.

+ Location: Rodney, New Zealand
+ Programme: Family House
+ Client: Private Owner
+ Site area: 2.5acres
+ Built area: 270sqm
+ Status: Built
+ Award: Overall winner of The Residential Concrete Sustainability Awards sponsored by Cement & Concrete Association of New Zealand (CCANZ)
+ Shortlist: FuturArc, Residential House, International Competition, Singapore
+ Credit: Duncan Firth, Milti Stefadouros