A fresh approach to design to achieve sustainability goals

Zero Energy House

The importance of design

The most critical factor to the performance of any building lies in its design. Not only is design key, it's the most cost-effective component in achieving Zero Energy. Shay Brazier and Jo Woods’ Zero Energy House in Auckland was able to achieve the biggest performance gains at the conceptual stage, without any capital investment, by incorporating site location, solar aspect, building orientation, and the roofing needs of the solar system into the design.

Design can also have a direct impact on building cost; a mistake made at the design stage can be very expensive to fix part-way through build, or sometimes so expensive that it can't be fixed and needs to be endured for the life of the building.

Setting energy goals for the design

The outcomes of the design process are a series of plans and details based on the goals established by the clients and the design team at the beginning of the project. For most houses the goals are around liveable areas and the aesthetics of the building. Shay and Jo had those too, but in addition they set the goal of Zero Energy.

Zero Energy is just one of many possible energy goals for a building. Homeowners planning their own projects could require a certain percentage of their energy to come from solar (as is being done more and more in the UK) or they could stipulate a Homestar rating they want the house to achieve.

It's important to remember the Building Code focuses on the bare minimums to ensure occupants’ health. Unless design goals are set to exceed those requirements, the end result might be a house with minimum standards of building performance.

An integrated design approach

Achieving an energy performance target requires input from multiple perspectives. In the case of the Zero Energy House that input was from A Studio Architects, a thermal engineer (Jo) and solar engineer (Shay). More often than not engineers are brought in after the building envelope has been specified by the architects to meet the liveable space requirements of the client. They then have to work within the constraints of that envelope to try and make the building perform, often having to compromise. The approach taken by the Zero Energy House is called ‘Integrated Design’. Rather than working sequentially with, first, the architects, and then the engineers, all parties work in parallel right from the beginning, integrating building performance into the design.

Performance vs. liveable area?

8m² was shaved off the building during design which saved enough money to pay for both the solar hot water and PV systems.

New houses are usually designed with a focus on liveable area, and the goal is often to maximise it within the constraints of the district plan’s limitations on the site. However, a larger house is unlikely to perform as well as a smaller one, partly because bigger spaces require more heating. With an energy target there may be a degree of balancing building size vs. energy performance.

But does a smaller house necessarily mean less liveable area? Houses being built in Auckland these days are 50% bigger than they were a generation ago¹. Is that extra space actually needed - or even used? It depends on the needs of the building inhabitants. For the Zero Energy House Shay and Jo specified what they wanted in terms of functional living area and designed the smallest building envelope that could provide that. This is a different approach to expanding to the edges of allowable building planes to make the house as big as possible without thinking about how it will be used.

Another benefit of designing a smaller, more efficient building envelope means it frees up money to spend on other things that might improve the performance of the house. For Shay and Jo, it was the systems that provide energy. They shaved 8m² off the building during design (~4% of the size) saving enough money to pay for both the solar hot water and PV systems.

Building vs. operating costs

A 200m² house could have a cost-to-operate per square metre of $400.

A key figure people track when designing and constructing a new home is the cost to build per square metre, which dictates how much homeowners will need to borrow and pay back over their 25-year mortgage term. But there's another cost that is rarely thought about - the cost to operate. At the time the Zero Energy House was built, it was estimated that if electricity prices continued to rise as they had in the previous decade, over 25 years a house the same size of the Zero Energy House could expect to pay $80,000 for electricity². In a 200m² house this equates to $400 a square metre. Spending this money on the design and build upfront to minimise or avoid that operating cost in the future is an alternative that made sense for Shay and Jo, even before considering the environmental and health benefits.

Footnotes
  1. Driving Forces in the Auckland Region, Auckland Regional Council, p28.
  2. New Zealand energy data file: 2010 calendar year edition, Ministry of Economic Development (2011), p130-131.

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