A recent Auckland City Council study into the living conditions of well over a thousand residents of newly constructed terrace and duplex housing found, amongst other concerns, that often the occupants were saying their homes were much too hot in summer. It was reported that this was put down to poor window placement, minimal shade and a lack of natural ventilation as the main features of the problem dwellings. I found it interesting that the most common solution presented from some commentators and the listening public was that wider eaves were needed so as to provide more shading. The pathway to a more comfortable interior environment in summer is much more complex and nuanced than that. In my Detailed Bblog of October 2021, 'Summer Cooling for Medium Density Housing', I discuss the unexpected consequences which could arise from the then political parties’ simplistic co-operation agreement to allow for three dwellings of three storeys each to be build in suburbia.

It is understandable that people would immediately think of extending eaves when looking to provide more shade as they are a common feature of the New Zealand house. The shadow they cast is very obvious, but how much solar protection do they actually offer to the interior? Perhaps the primary purpose of eaves is not to provide shade but rather to shed our regular rainfall away from the walls.

While it is difficult to design ‘best solutions’ for a particular site for most of the unpredictable dynamic environmental influences on dwellings such excess wind, rainfall, landslips, earthquakes, daily cloud-cover etc., the diurnal cycle of the sun and the position of its constantly changing seasonal annual arching pathway are completely predictable and therefore can be incorporated into the design process as an environmental constant. Also the variations in potential passive solar heating gains throughout the year can be easily accounted for. There is no need for duplex, terrace, and apartment housing to unquestioningly follow the passive heating and cooling design and construction solutions of the past and present common standalone house; new intelligent solutions are needed. 

In my Detailed blog of April 2015, 'Shading: It is Not All Bad' I wrote of the positives and negatives of permanent shading and the need to consider this in the early stage of the design process rather than being “…an afterthought add-on.”. A while back I travelled in Central and Southern France, and in Spain, during the ‘regular’ heat-waves they were having at the time. Also last year I was in Turkey for six weeks. Given the wide range of local summer climates I experienced (high interior plateaus in France and Turkey, to Mediterranean coastal zones in Spain and Turkey, and everything in between), I was able to take particular notice of the wide variety of ways the ancestors had developed to passively modify the environmental conditions in their particular locale to make their lives more comfortable. Modern buildings rely on network energy consuming air-conditioning systems instead. If we design intelligently we wouldn’t need these mechanical aids for our modern dwellings, except in unusual circumstances. 

In Europe the old tried-and-true window shading acknowledged the sun; horizontal at the South (our North) quadrant and vertical at the West and East quadrants. These were further refined by sometimes being movable and/or louvered, and could even act as storm-shutters in relevant climates. There were also excellent examples of these old methods being thoughtfully adapted to modern materials and forms. The common feature was that they only dealt with the openings in the exterior walls at each of the openings. Walls were dealt with separately, usually by being of significant thermal mass, and by colonnades at ground level, and by being recessed well back into the building façade where appropriate. The colonial English had their method for protecting the external walls from the tropical sun — the wide verandas as seen in Australia, India, Africa and elsewhere, with large folding-back doors allowing the breeze to flow through the interior during the hot summer.

I strongly suspect that the growing problem of summer over-heating of medium-density housing, especially in Northern NZ, has a lot to do with the recent changes to the NZ Building Code, clause H1/AS where the now usual method of showing compliance requires construction R-value R6.6 throughout the whole country for the roof insulation. Refer to my Detailed Blog of July 2024 'Does NZ Building Code: Clause H1 - Energy Efficiency (5th ed.) Need Change?'

The problem of summer over-heating in our future housing cannot be mitigated by making cosmetic changes, a holistic and considered approach is necessary. My Detailed Blog of April 2014 'Insulation, Glazing & Thermal Mass: Is There a Simple Relationship'; and a follow-up in December 2014 'Insulation, Thermal Mass & Glazing: The Juggling Game', discuss the reality that our houses exist in a dynamic exterior setting.

Most designers are familiar with the basic concept of thermal mass as a means of moderating the interior spaces of dwellings, but then cover the concrete floor with an insulation layer of fitted carpet which much reduces the heat-flow into and out of this otherwise very useful thermal mass thereby resulting in a much greater 24-hour temperature differential within rooms. (Actively heating the concrete floor is an entirely different and separate subject.) The party-walls between dwelling units are now usually constructed of light-weight and low-mass materials so they add to the over-heating problems rather than tempering them. In the past concrete blocks were used for these walls. 

Window size and orientation, and whether or not they are openable, also have a major influence on the extent of the range of interior temperatures and therefore the comfort levels for the occupants. Despite the dominance of these openings on the interior thermal performance of homes, this aspect has to be ignored (or the designer’s intuition is applied, often with adequate results), due to the complexity and economics of trying to manually calculate a sensible result for the effect of each window.

The summer over-heating trend for medium-density housing cannot be resolved separately by each developer and designer, instead there need to be a societal and market-forces acceptance that we cannot build as before.