BRANZ influencers

This Issue This is a part of the Celebrating success feature

By - , Build 189

For many decades, BRANZ research has successfully fed into Acceptable Solutions and Verification Methods, building laws and standards, but the work is often not visible. Here, we give a behind-the-scenes view of some of the mahi (work) we have been doing.

WHEN IT COMES to heavy lifting work, few sectors can match the construction industry. Although some of the toughest jobs don’t involve tower cranes or Hiab trucks – they are the intensive lab tests and computer calculations that underpin updates to all the documents that regulate the industry.

Informing solutions and verifications

Given that changes can mean increased costs and people having to learn new building methods, materials and technologies, building a solid floor of reliable evidence to justify them is critical.

The 5th editions of Building Code Acceptable Solution H1/AS1 and Verification Method H1/VM1, announced last November, are good examples. They hold the results of BRANZ research and calculations. Roman Jaques, Jamie Sullivan and others at BRANZ carried out extensive modelling work, including around the increased number of climate zones and the H1 values in final version. Other scientists modelled the thermal performance of windows and slab-on-ground floors.

Ensuring thermal compliance

John Burgess, a BRANZ Senior Scientist, in association with the Window and Glass Association New Zealand (WGANZ), produced the table in H1/AS1 (Table E.1.1.1) that shows construction R-values of selected generic vertical windows and doors.

It allows architects and designers to see at a glance just what will comply with the new H1/AS1 and what won’t. This is an incredibly useful basic level of guidance, especially when you bear in mind that most windows specified and installed under the earlier version of H1/AS1 will no longer comply.

The table was calculated using the Window Energy Efficiency Rating System (WEERS), also developed by John and others at BRANZ in close association with WGANZ. This calculates the thermal performance of windows for housing and small buildings.

The rating system is used by window suppliers who can provide a WEERS certificate that records the R-value of each window and the R-value for the house lot. This helps architects and designers demonstrate that a building complies with Building Code requirements. The calculation used by WEERS is also consistent with the new H1/VM1 window construction calculation methodology.

Modelling concrete floors

Ian Cox-Smith, BRANZ Building Physicist (Thermal), was involved in the development of the new slab-on-grade requirements in H1/AS1. Ian did the modelling for the extensive tables in Appendix F that give construction R-values for different slab-on-ground floor types.

As with the windows table, these tables provide crucial guidance for architects and designers on what slabs will comply with the new requirements and what won’t. Some smaller slabs will need additional insulation to comply with the updated H1/AS1 requirements.

Ian also helped in writing the text that references the ISO/EN standards. ‘It was important to MBIE to not only reference international standards but to do it in a way that was quite specific so that anyone doing modelling for particular floor systems would get results that were consistent with the generic tables,’ he says.

‘We were also part of the industry working group that discussed the industry feedback on the draft slab-on-grade proposals. The slab-on-grade requirements were not included in the original draft of H1 that went out for public consultation, so it needed separate industry consultation.

‘The BRANZ feedback on the H1 proposals also took into account the slab-on-grade floor research when discussing what we thought would or could be achieved overall by changing the energy efficiency clauses.’

Putting corrosion on the map

BRANZ Senior Corrosion Scientist Zhengwei Li’s work contributes to many building controls involving protection against corrosion. This is a field that BRANZ has had considerable input into for a long time.

From the late 1980s, BRANZ measured the corrosion rates of various metals (mild steel, hot-dip galvanised steel and aluminium) at 168 locations across the country. This research largely determined the exposure zone maps in NZS 3604:2011 Timber-framed buildings. Zone B is the least exposed, at the least risk of corrosion, while zone D on the coast is the most exposed.

In the 2010s, BRANZ measured the first-year atmospheric corrosion rates of mild steel and hot-dip galvanised steel samples at 61 sites. At most testing sites, the new data was comparable with the old data collected in the 1980s. At a limited number of testing sites however, such as Auckland Airport, Tiwai Point and Greymouth, significant changes were seen in corrosion rates. This indicates that the atmospheric corrosivity in some areas is changing and suggests that an update is necessary to adjust zone boundaries in some areas.

Zhengwei’s research from 2016–18 found that several other amendments should also be made to what is set out in NZS 3604:2011:

  • In areas with geothermal or industrial influences, including Rotorua, Tikitere, Rotomā, Kawerau, Te Teko and Edgecumbe, the atmospheric corrosivity category should be increased from zone B to zone C.
  • Specific engineering design is currently required for buildings constructed within 50 m of a geothermal hot spot. Research suggests that it would be appropriate to increase the current boundary from 50 m to 500 m.

BRANZ has recently updated the New Zealand atmospheric corrosivity map based on research findings and made a submission to the team currently working on the update of NZS 3604 to carry changes into the new version of the standard. A contribution was also made to SNZ TS 3404:2018 Durability requirements for steel structures and components.

Housing surveys and healthy homes standards

Increasingly, BRANZ is working in collaboration with universities, government agencies and other bodies to get bigger bang for the buck.

A good example is the Pilot Housing Survey, a partnership between BRANZ and Stats NZ with co-funding from MBIE. In 2018/19, independent assessors visited 832 houses across the country, recording information on house condition and energy efficiency. This was the largest national housing assessment of its type since 1937.

At the time the survey content was being designed, the new healthy homes standards were being developed. BRANZ worked closely with the team at MBIE behind the standards to inform and shape survey questions, recognising the rare opportunity provided by the survey to collect important data.

The Pilot Housing Survey confirmed the findings of earlier BRANZ House Condition Surveys that, on average, rental houses are in poorer overall condition than owner-occupied houses. They are more likely to have moderate or worse visible mould present, ill-fitting/warped windows or exterior doors and gaps around windows and exterior doors.

This substantial body of research provided unequivocally clear evidence of the comparatively poor standard of rental housing and the need to improve the living conditions these homes provide.

Other work within the BRANZ Warmer, drier and healthier buildings programme has complemented changes to the Residential Tenancies Act and the Healthy Homes standards, with significant work for the standards in particular by Vicki White and Mark Jones. The research within this programme has also played a role in finalising an internationally recognised conceptional framework for housing quality, which will contribute to better housing quality statistics.

Part of the collaborative approach of many projects such as the Pilot Housing Survey is making data available to outside researchers. As part of the survey, BRANZ worked with Stats NZ to make the dataset available to researchers in a secure environment through its Data Lab and the Integrated Data Infrastructure (IDI).

Carbon and the future

One of the most urgent programmes of work in BRANZ is supporting the industry to decarbonise. New Zealand is committed to achieving a net-zero carbon economy by 2050. While there is no single agreed level of the contribution that buildings and the construction industry contribute to New Zealand’s greenhouse gas emissions, it is generally thought to be around 15–20%. The industry therefore has a big challenge in coming decades.

Once again, this is an area where collaboration is crucial to achieving gains within pressing timeframes. Scientists from BRANZ and Massey University developed a method for calculating a carbon budget – the amount of greenhouse gases that a New Zealand house could allowably emit while still moving towards New Zealand’s 2050 net-zero carbon goal.

Transition to a zero-carbon built environment programme science leader Dr David Dowdell has also led development of a suite of carbon tools for carrying out life cycle assessment and carbon footprinting of proposed building designs. BRANZ developed the Homestar Embodied Carbon Calculator (HECC) tool for the New Zealand Green Building Council. The HECC tool is based on a platform from the BRANZ tool CO2RE and facilitates calculation of an estimated carbon footprint of a dwelling.

Supporting higher-density housing

Almost half the new homes consented around the country in 2021 were multi-unit housing. The move to higher density is already firmly entrenched in Auckland, where multi-unit homes account for two-thirds of all new homes consented, and in the Wellington region.

BRANZ has had several work projects under way in this area, one of them addressing the weathertightness of claddings of mid-rise buildings. In the changes in Building Code Acceptable Solutions and Verification Methods announced in November, the second edition of E2/VM2 (covering buildings up to 25 m in height) now cites the evaluation method BRANZ EM7 Performance of mid-rise cladding systems v3 (June 2020) as the primary means for demonstrating compliance.

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