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Making New Zealand homes warmer, drier, and healthier

If you’re a Homeowner, Architect, or Property manager and unaware of the recent changes to insulation requirements and how they could affect the structural engineering of any new builds, read on!

In Brief

New Zealand has a history of building homes that are cold, damp, and energy inefficient. Recent changes to the New Zealand Building Code have been made to rectify this. In this article, we will go through the details of this change through the lens of a structural engineer, including the pros and cons. But in brief:


· Warmer, drier, healthier homes.

· More energy-efficient homes.

· Potentially less structure required for roofs (when SIP panels are used)

· Refined insulation requirements for different climate zones around the country.


· Increased build costs.

· Adjustment period while we all get used to the new requirements.

What are the changes?

Hikinia Whakatutaki - The Ministry of Business Innovation and Employment (MBIE) has recently updated the New Zealand Building Code with a change in climate zones and insulation requirements for these zones. The changes are specifically to H1/AS1 and H1/VM1 of the Building Code and increase the minimum insulation R-Values for roofs, windows, walls and floors for new housing and new buildings.

You don’t need to be a meteorologist to know that New Zealand has a wildly varying climate depending on where you live. Luckily the minimum insulation levels will vary, with homes in the coldest parts of the country needing more insulation than those in the warmest parts.

Although insulation and thermal efficiency is not typically something we as engineers need to consider, the outcomes of these changes will affect everyone, including homeowners, builders, architects and property developers.

Before we get into the details of the changes, let's discuss some key terminology that’s used in the Building Code. What's an R-Value?

Put simply, the R-Value measures how well a two-dimensional barrier, such as a window or glass wool insulation resists the conductive flow of heat. R-values can be affected by the thickness and composition of the material, and the direction of heat flow. A higher R-Values means a material or barrier is a better insulator. R-value is the industry standard when comparing insulation types and amounts of insulation; however, it is by no means the complete way of understanding the thermal conductivity of your house. To get a better understanding of the full thermal conductivity, U-Values should also be used. U-values won’t be explained in this article since the Building Code only mentions R-Value, but if you want to learn more about the difference, this article has a good explanation of them.

Until recently, there were 3 climate zones for the entire country. However, this has been changed to 6 climate zones which allows for a better representation of each specific zone. The six climate zone boundaries are based on climate data from NIWA and take into consideration territorial authority (local government) boundaries.

Why are these changes happening?

New Zealand building insulation standards are significantly lower than homes in other countries with similar climates and similar economies. Having insufficient insulation in your home means that it is more energy-intensive to heat in winter, and more energy-intensive to cool in summer.

For New Zealand, this is most crucial in winter, and insufficient insulation means that many homes are almost impossible to heat effectively and end up cold and damp. To highlight the differences compared to other countries, when MBIE first proposed the changes, they did comparison graphics to other countries for each option they were considering. Note that 'status quo' is what the current regulations require. The actual changes after consultation with the industry are a mix between Option 2 (comparable) and Option 3 (going further)

In short, it highlighted that R-Value minimums, particularly for our roofs, were almost half that of comparable countries with comparable climates.

The Changes in Detail

To lessen the impact of changes to the building industry, the minimum requirements will be increased in steps over the next year. 3 November 2022 Changes Before the changes, the minimum R-value for windows in all climate zones was 0.26. As of now (after 3 November) it is 0.37. 1 May 2023 Changes

On this date, the biggest changes will happen. The minimum R-value requirements for roofs, walls and floors increase for all climate zones. See the table below for the changes

2 November 2023 Changes

The R-value for windows will again increase, to 0.46.

What are the effects and structural implications?

The increases in insulation requirements for walls, floors and windows will not have a dramatic effect on the building industry in the areas we work in as we note the new minimum values are typically already being met. This also goes for the structural implications.

What will have a large effect is the planned increase in roof insulation requirements.

A higher level of insulation can be achieved in many ways which we are sure to see over the coming years. One simple option would be to double up the layers of ceiling insulation. However, there are other options out there that not only increase ceiling insulation, but may decrease bracing demands, framing, and beam sizes. What magical option is this? Structural Insulated Panels! Structural Insulated Panels A less conventional approach to increasing roof insulation R-Value (in New Zealand anyway) would be to use Structural Insulated Panels (SIPs). SIPs are a prefabricated building system comprised of two layers of structural board with an insulating layer of foam in between. It can be used to construct walls, floors, and ceilings.

They come in a range of thicknesses depending on the R-value required and the span of the panel, but they are typically in the range of 200mm – 300mm thick.

As SIPs can span between supporting members (for example between the top plate and ridge beam), in some situations this may lead to SIPs replacing most of the traditional timber framing required for a roof structure while providing superior thermal performance.

SIP panels are also lighter than traditional timber framing, so may lead to a reduction in bracing demands and the sizes of beams supporting the roof. Something to consider for your next project!

Will these changes cost more?

In short, the answer is likely yes. Typically, the higher the R-value of an item, the higher the costs will be. Although this will result in higher build costs, the long-term savings in energy costs and the overall increased building performance will give us warmer, drier, and healthier homes for the future. When MBIE released their consultation documents, they also released a map of what the expected extra investment/cost would be, and the expected energy savings for each option. Note that as mentioned before the actual regulation changes are in between Option 2 and Option 3

As you can see, investment or cost is expected to increase from between 3.2% to 12.1% but the energy savings from this investment is expected to be between 36% and 68%!

What's next?

These changes were enacted to bring us in line with international standards and provide healthier, warmer, and drier homes for all New Zealanders. While this update was released back in November 2021, its only just now started to be enforced in new buildings. If you are unsure how this might affect your build, planned or otherwise, give us a call and we can help point you in the right direction!


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