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17 February 2014

Does Passive Thermal Design Have to Mean Greater Cost?

There is a lot of genuine misunderstanding and many urban myths – and from time to time even ‘greenwash’ – regarding the rapidly developing area of passive thermal design.  It is become more readily accepted as an efficient way to minimise the use of non-renewable energy while at the same time maintaining comfort levels and standards for our buildings.

Replacing non-renewable energy supplies with renewables gives long-term benefits without continual expense.  It also assists sustainability, reduces total energy use, and maximises the ‘free’ energy from the environment and the sun.  Of course there is an initial capital cost, but few running costs

Some believe that designing with passive thermal performance and sustainability in mind will inevitably increase building cost, which is not strictly true.

The installed cost of a window is essentially the same no matter which wall it is fitted in, but the orientation of the walls greatly affects the passive thermal gains or losses for the room i.e. a window in the south wall of a room will cool the space, while the same window in the north will heat the room for part of the day. In either situation, there is no difference to the construction cost.  In selecting from similarly priced sites in a new sub-division, one that allows for the garage on the south side and a more favourable orientation of the plan layout would give lower long-term heating/cooling expenses over the life of the building at no extra construction cost. 

It is an established economic principle that over the lifetime of a building, the operating expenses far outweigh the initial capital cost – meaning that any design feature that reduces energy costs is an excellent (essential) investment.  Of course, in my opinion, this should not override the ‘liveability’ and usefulness of the building.    

In these regular writings I propose to bring useful information and stimulate discussion, while being happy to be challenged as there is a range of diverse opinions out there and more than one solution for any problem.

I am a registered architect (RAB# 1372) involved, as EcoRate Ltd, with passive thermal design and the objective analysis of designers’ and architects’ projects using the AccuRateNZ (HERS) thermal simulated software brought to New Zealand by EECA for their Home Energy Rating Scheme (HERS).  I am also a HomeStar Practitioner and Assessor.  Being a practicing architect, I understand the importance of ‘buildable’ solutions for design and detailing.  My website is

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