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26 August 2019

Holistic Approach Key to the Energy Efficiency of Building Products

house build

For this month, August 2019, the EBOSSNOW feature topic was ‘Energy Efficiency’ with a wide variety of case studies and products featured. As is to be expected, each of these presentations deals with its product or case study in isolation from the others, which is logical as the companies’ interests and expertise lie in their particular products and services.

Readers will understand that while each of these products in themselves contributes positively to energy efficiency, they do not each determine the overall performance of the building they are used in. As a common example, no matter how effective a winter coat is in keeping you warm, if it is not zipped up then you will be cold as your body heat escapes through the opening. Similarly, in a building heat is ‘lazy’; it doesn’t bother to struggle through the quality insulation, it just moves to the point of least resistance and escapes from there. When thinking of summer cooling the same principle applies, as also when considering each of glazing and thermal mass, and then the interaction of all three.

There is an old adage: a chain is only as strong as its weakest link. This needs to be remembered when considering the overall thermal performance of a building. This becomes complicated by the fact that for buildings the weak thermal link is usually glazing (and therefore surely it should be removed!). Of course, glazing is essential for most buildings, and exposed thermal mass can be a major positive or negative when aiming for maximum passive solar performance. In my December 2014 blog post, Insulation, Thermal Mass and Glazing: The Juggling Game, I discuss the need to find the ‘sweet spot’ which not only varies between any two buildings but also with a change to the orientation of a particular building. Improving a building’s thermal performance is not a simple case of just throwing in more insulation as the media regularly suggest to the public. A holistic approach is necessary.

Getting the balance even reasonably right for the three fundamentals is hard enough without then having to introduce all the other important non-thermal design factors which must be given due consideration. In the past, designing the thermal aspect of dwellings, especially for passive solar performance, usually involved intuitively doing what had been done before rather than using robust objective measures. Until the late 2000s when the government through EECA introduced the HERS (Home Energy Rating Scheme) star-rating evaluation process, there was no thermal simulation computer software available for homes in the New Zealand environment. This process was overtaken soon afterwards by the more wide-ranging Homestar sustainability assessments.

With the rapidly expanding range of thermal control materials, products and construction methods now available, it is much more important to be able to objectively calculate the effects of the interactions which can reduce their promoted performance, such as the need to incorporate materials which provide thermal bridges (the most common example being the studs in a timber wall). This also relates to products which don’t promote thermal characteristics but do have a positive influence, such as acoustic insulation.

Through EcoRate Ltd – Architect, I provide independent analysis and advice (using the HERS thermal simulation software) to architects, designers, builders, manufacturers, and others in the construction industry, including those proposing building a new home.

For more information on your passive solar design needs, please contact Keith at Ecorate on 021 890 251,, or visit

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