New Zealand is in the midst of a multi-faceted housing crisis which is primarily focused on affordability and housing shortages. However, housing quality also plays a part in this crisis with cold, damp and mouldy housing strongly correlated with poor health.

Approximately two-thirds of New Zealand housing is uninsulated and inadequately heated. This can lead to low average indoor temperatures, which are linked to higher respiratory illness-related hospital admission rates in winter (74 per cent) and excess winter mortality (20 per cent greater than other seasons¹).

The 2018 census included questions on mould and damp for the first time. It found that 17 per cent of all homes were affected by damp and when compared with owner/occupier homes, renters were seven times more likely to report damp. This situation is further exacerbated by poverty, with a quarter of New Zealand households estimated to be in fuel poverty (defined as a situation where a household needs to spend more than 10 per cent of its income on all household fuels to achieve a satisfactorily warm indoor environment).

For new homes, the building code is the legislative mechanism that sets the minimum standard. However, a 2017 review by the International Energy Agency found that the current New Zealand building code is below the standard required in most IEA countries with comparable climates. This has led to all New Zealand housing (encompassing both older vintage and newly constructed housing) being denounced as poor quality. This is reflected by the New Zealand Green Building Council (NZGBC) who states ‘New Zealand homes aren’t good enough; all too often, they are cold, draughty, expensive to heat’².

Green building is often viewed as a solution to the cold and damp housing crisis with the NZGBC using rhetoric like “A 6-Homestar rating or higher provides assurance that a house will be better quality—warmer, drier, healthier and cost less to run—than a typical new house built to building code”³.

Both government (Kāinga Ora) and industry (Panuku) have adopted this narrative, applying Homestar as a mechanism to deliver warmer, drier houses than what might have been delivered through the use of building code alone. Kāinga Ora states ‘its move to 6 Homestar means its new homes will far exceed Building Code standards for warmth, dryness and health”⁴.

However, not only has the ability of 6 Homestar to deliver warmer, drier dwellings than building code not been empirically tested, very few investigations have empirically contrasted the performance of the current building code against older vintage dwellings.

My doctoral research investigated whether there were any differences in indoor environment quality (IEQ) performance of 29 social housing case-study dwellings (13 green certified, seven code compliant, nine older vintage) in Glen Innes, Auckland, concurrently measuring the temperature and humidity in the living rooms of these dwellings. The research is unique as it is the first time that older vintage dwellings have been disentangled from newly constructed, code-compliant dwellings with the performance of both contrasted against the performance of newly constructed green-certified dwellings.

Wintertime cold and damp⁵

Data loggers recording temperature and relative humidity were utilised, in conjunction with empirical analysis, to confirm that whilst older vintage (OLD) case-study dwellings did spend significant amounts of time (71 per cent in winter) below the World Health Organisation’s (WHO) 18°C recommended minimum temperature threshold, so did newly constructed dwellings.

The code-compliant dwellings (NEW) spent 64 per cent of the time under 18°C, in contrast to 56 per cent for the new, green-certified dwellings (6HS). Whilst the green certified dwellings spent less time below 18°C compared to the code-compliant dwellings, no statistical difference was identified between the interior temperatures and predicted comfort levels.  

Living room humidity was also evaluated with two clear conclusions drawn. The first, that all dwellings studied spend the majority of time with high internal-moisture loads in the living room regardless of vintage and green certification. The green-certified case-study dwellings were outside the optimal relative humidity range (40 per cent to 60 per cent) for 86 per cent of the time in winter, in contrast to 94 per cent for the older vintage and 83 per cent for code-compliant dwellings.  

In addition, all dwellings had consistently high internal absolute humidity (>8 g/kg). Given the decrease in outdoor absolute humidity in the cooler months of the year, this may indicate two things: i) dwellings may not be adequately ventilated with outdoor fresh air; and ii) any outdoor air that is present may not be adequately heated to depress the relative humidity.

Summertime overheating⁶

Newly constructed housing was observed to have consistently hotter living rooms than the older vintage dwellings. The green-certified case-study dwellings were warmer than the WHO recommended healthy temperature threshold of 24°C for 75 per cent of the time over January through March. This is the equivalent of being potentially uncomfortably warm for more than 18 hours per day, over the period. The newly constructed code-compliant case-study dwellings spent 58 per cent of the summer over 24°C whilst the older vintage case-study dwellings were over this threshold the least (43 per cent). The green-certified case-study dwellings were also predicted to be too hot for 16 per cent of the period, twice as much time as the older vintage case-study dwellings (8 per cent).

Policy implications

With no requirements in either the building code or Homestar for ongoing performance monitoring, this research represents the first instance where older vintage dwellings have been measured alongside newly constructed code-compliant dwellings and green-certified dwellings.

The research found that both building code and 6 Homestar were not able to fully remediate ‘cold and damp’ in the case-study dwellings, with the newly constructed code-compliant and green-certified beneath 18°C for 64 per cent and 56 per cent of the time, respectively. Both also spent minimal time in the optimal relative humidity range.

With the health effects of overheating and suboptimal humidity documented in the academic literature the inattention to these critical elements of building performance is concerning and should form a key focus of government legislation, building standards and green building standards moving forward.

ArchitectureNow reached out to the New Zealand Green Building Council for comment. Chief Executive Andrew Eagles said the following:

“Homestar was developed alongside the building and construction industry to encourage our sector to build above New Zealand’s woeful Building Code for the benefit of all. As part of our commitment to continuous improvement it is regularly updated to ensure it aligns with best practice. The current Homestar tool is in its fourth version, and we’ve had huge interest and engagement from the sector in the last year as we work through creating the new version five. In creating rating tools we rely on input from the sector, the expertise of our staff, research and international best practice.

“We know that a third of New Zealand’s homes are damp and mouldy. There is an unforgivably high rate of respiratory disease. We are driven to ensure those sorts of woeful statistics aren’t a reality for generations to come.

“Part of our collaborative approach in creating and adjusting the tool is of course to take into account independent research. Research is an important input alongside other feedback from the sector. We have been aware of the research by Rochelle Ade and Dr Michael Rehm for several months and have worked to see what, if any, insights we can take from it.

“We understand some academics have contacted the researchers, the journal that originally published their work, and us here at the Green Building Council. It would appear there are concerns over the research design, sampling and methodology adopted. We’re now letting the scientific process run its course, and for the concerns over the research to be addressed.

“There is a great opportunity for healthy homes campaigners and research bodies to work together to improve our homes. We would like further research to cover the whole of New Zealand, beyond Auckland where the climate is more temperate than other parts. We would also like to see a larger sample size to enable like-for-like comparison of properties, rather than comparing homes to apartments, and to include an examination of whether heating is used. We are currently supporting research of Homestar homes by Massey University, and we’re in the process of facilitating other monitoring projects of high performing homes and how they perform.

“We’re hugely proud of Homestar, and all the homes in Aotearoa that have been verified using this standard – from the 6 Homestar homes, which we say is the bare mimimum New Zealanders deserve, to the world leading 10 Homestar homes.”

Panuku similarly has plans to do more ongoing monitoring of their housing projects

Panuku Development Auckland’s head of corporate responsibility, Kristen Webster, offered this response: 

“Due to a general interest we have in the performance of dwellings delivered by our development partners on our sites, earlier this year Panuku took the proactive approach of installing sensors of the same kind used in the study on a 40 unit residential development on one of Panuku’s sites in order to obtain data of our own.

“Primarily we are looking at temperature and humidity within the units as measures of both health and comfort. At the end of the year we will be analysing the data to ascertain the performance of the building across all seasons.

“We are keen to ensure that Homestar is delivering the outcomes we envisage of warm, dry, and comfortable homes. We also intend to marry up the technical data obtained with some occupant surveys to find out how residents feel in their homes. If any issues with these dwellings are identified, we will be looking at what design solutions there could be to ensure that we take these learnings into future developments.

“Panuku (via its predecessor agency Waterfront Auckland) adopted the use of Homestar in Wynyard Quarter in 2013 and in 2017 adopted it for use on all other developments. At the time this was the only rating tool in mainstream use in the New Zealand market. 

“Panuku acknowledges that Homestar 6 is not the measure of a high-performance green building and is not intended to be so. Panuku has an approach to set minimum standards to ensure that all buildings are above building code, but we encourage our development partners to deliver better. Our intent is that these standards will be raised over time to reflect changes in the market. 

“We will continue to stay abreast of residential green rating tools and any alternatives. In the event a more suitable tool is developed or discovered we would be open to its use on our projects. In the past we have considered development of a bespoke set of standards but have discounted this due to the difficulties with ensuring compliance. Use of an independent third-party verified performance rating is considered to be our best option.”