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24 February 2015

Site: It is Never Too Early to Begin

Passive thermal design, be it for heating or cooling, should not be left until the stage where the selection of insulation and thermal mass materials is being made. Nor should it be held off until the elevational treatment of the windows is being finalised. For most houses the normal scenario for these aspects is to be put aside for tweaking at a later stage; a case of re-arranging the deckchairs on the Titanic.

For a reasonably sloping site most architects and designers give thought to the possible foundation structure as an aspect of the initial design and for any influence it may have on the owner’s brief. Is it more 'sensible' to use a pole-type sub-structure – be it steel or timber – so as to lightly touch the site? Or will a cut-and-fill approach with retaining walls be more appropriate? These decisions will have a strong influence on and be influenced by the brief, space planning, aesthetics, materials selection and buildability, etc. Even for a flat site the structural foundations are considered at an early stage if there is a suspicion of possible difficulties such as liquefaction, or in Auckland for example, the potential for a partial lava tongue or void below the proposed house. These structural investigations are usually undertaken early in the design process and can result in the rejection of the site, or at least making the best of the given negative situation. A wise purchaser of a potential house site will include a structural evaluation in their considerations. Why isn't it done for the thermal design aspects?

When it comes to the influence of the passive energy aspects of a site on the design of the proposed house, much less (if any) consideration is given to these compared to the view from the site, ease of transport, closeness of amenities and status of the locality, etc. While structural difficulties of a site may result in an increased cost, this is a one-off expense, whereas the additional 'imported' energy expenses (heating and cooling), are continuous over the life-time of the building. 100+ year old houses are sought after, and even the popular state houses have been around for three-quarters of a century. We are now having to cope with the (lack of) passive design decisions made in the past; why should this continue into the future? Even if you decide to sell-off your inefficient house you are still buying into a market which does not give particular value to the free energy available from the environment.

The majority of services I provide are to assess the final working drawings for compliance with NZBC-H1 (Energy Efficiency) as a Building Consent application is about to be made. Even so, I take heart in that more projects are being brought to me as working drawings are about to begin, and even some at the Preliminary/Developed Design stages.

While clever design can make the most of a particular site, it is the site itself which is the primary determinant of the passive energy performance of the built house. As a silly example, a site in the Cook Islands will require less network energy than one on Campbell Island, but if you work on the later then the former is inconvenient even if there is an energy cost saving.

Every house requires a site, but is there such a thing as the 'ideal piece of land'? Especially when the myriad of often conflicting features are all considered, so normally the best has to be made of what is available. Passive thermal design is just one aspect. An east facing site just below the ridge line will lose in winter the low western sun, especially if a high fence or dense hedge is necessary for privacy from the footpath above, but careful and clever design and material selection can capture the morning solar gain and make it last until well into the evening. The southern face of a steep sided valley, such as Aro Street in Wellington, can provide all day sun if it is orientated east-west, whereas the same valley aligned north-south will have much less desirable sites, although a design with its windows in the roof will substantially negate the orientation.

There is no such thing as the ideal site but a prospective purchaser of a building section, or of an existing house, can give careful conscious consideration to the passive thermal potential of the property so as to maximise their investment and thereby reduce the ongoing cost of occupying the land.

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