Effective from 27th November 2025, the 6th edition of clause H1 (Energy Efficiency) of the NZ Building Code (NZBC-H1) became the document setting out the requirements to be complied with for consent. By now residential design and construction practitioners will have become familiar with the changes, accepting that the Schedule Method has been removed from the NZ Building Code as a means of demonstrating compliance. Even so the two primary pathways, namely the Calculation Method of ‘Acceptable Solution H1/AS1’, and the alternative ‘Verification Method H1/VM1’ have been retained.

For the Calculation Method of Acceptable Solution H1/AS1 compliance is achieved by demonstrating that the heat loss through the thermal envelope of the Proposed Building (or alternatively individual dwellings in multi-unit buildings) is less than or equal to the heat loss of the Reference Building. Apart from a small reduction in the denominator of the 70% wall area of the Reference Building heat loss equations, the equations are the same as those of the 5th edition. Paragraph 2.1.2.11 specifies minimum R-values for the roofs, walls and floors for the Proposed Building. No significant change here.

For the Verification Method of H1/VM1 compliance is achieved by demonstrating (refer to paragraph 2.2.1.3) that the sum of the calculated annual heating load and annual cooling load of the Proposed Building (or alternatively individual dwellings in multi-unit buildings) shall not exceed that of the Reference Building. The construction R-values to be used for the thermal envelope of the Reference Building, as specified in Table 2.3.1.2, are the same as the denominators of the heat loss equations for the H1/AS1 Reference Building. Again no significant change. Many readers will have noticed that the R-values used for the Reference Buildings for both Edition 6 methods are essentially those listed for the Schedule Method of Edition 5 of NZBC-H1 — just the name has changed.

Slab-on-ground floors

Appendix E of H1/AS1 has a series of tables, Table E.1.2.1 and Table E.1.2.1A through to Table E.1.2.1X. These list Construction R-values for various levels of thermal insulation associated with concrete slab-on-ground floors. The insulation ranges from nothing to full underneath cover, and either with or without vertical edge insulation as an option.

I was interested to see that Paragraph 2.1.1.4 of H1/AS1, and paragraph 2.1.1.3 of H1/VM1 both have the same comment regarding Slab Edge Insulation.

“COMMENT: Slab perimeter insulation should be protected against water absorption, ultraviolet (UV) exposure, and impact damage. However, deviating from step 2 in section 10.3 in NZS 4246, encapsulation of slab perimeter insulation is not recommended as it can result in moisture getting trapped.”.

The Reader may be interested in my Blogs of November 2014 Is Slab Edge Insulation as Effective as it Seems?, and of May 2015 Slab Edge Insulation: An interesting Experiment. 

The NZBC-H1 is no different to the majority of other New Zealand Codes and Standards in that they specify thresholds for their subject matter, but not for associated matters. Users of the codes and standards often treat the threshold as maximums/minimums rather than starting positions from which better results can be achieved. The Schedule Method of H1-Edition 5 is a case in point. There was no requirement to achieve precisely (very difficult to do anyway) those R-values; they are just thresholds. Even when there is a comprehensive thermal analysis showing superior performance of a project the Schedule Method R-values could still be used to demonstrate compliance, without the hassle of defending the actual process used, because the proposed R-values would be better than the Schedule figures. Of course the comprehensive thermal analysis would be of particular benefit and value as a design tool for the designer and consultants, as well as for the client. 

At paragraph 2.1.2.1(a)(ii) of NZBC-H1/VM1 there is an example where a novel material can be used, rather than a particular R-value to show compliance. This enables its thermal mass to be incorporated into the NZBC-H1 compliance process. The material is ‘earth walls’ provided that they meet the requirements of NZS 4299:2024 - Earth Buildings Not Requiring Specific Engineering Design. Occasionally I have, using AccuRateNZ, simulated the passive thermal performance of earth houses. The latest was constructed of Structural Light Adobe (SLA) bricks, and demonstrated the positive benefits of passive thermal mass.

In my EBOSS Blog of February 2025, Passive Over-Heating: Does Internal Thermal Mass Make a Difference?, I discuss the benefits of thermal mass to moderate the diurnal temperature swings in a dwelling. I accept that the analysis of thermal mass is too complex to be incorporated into the body of NZBC-H1 as a general requirement.

The comment panel of H1/VM1, paragraph 2.1.1.1 lists some passive measures which can reduce or prevent overheating from excessive solar heat gains through the building’s thermal envelope so as to diminish dependence on active cooling systems.

Shading is the knee-jerk response to over-heating but it is not simple to create, and objectively evaluate, a scheme which will effectively handle the various and constantly changing conditions with the outdoor environment presents. Refer to my EBOSS blogs of April 2015, Shading: It is Not All Bad, and of October 2024, What Shading is Needed for Summer Cooling.

At present the NZBC-H1 concerns itself with just the thermal envelope of residential buildings, but if the summer overheating problem is to be significantly reduced and controlled then more sophisticated simulation methods will need to be available which would also consider the interior of dwelling as a whole structure, and calculate continually over a short time period on an annual cycle. BRANZ’s ‘Level’ Bulletin, dated 6 October 2022, “Passive Design – Thermal Simulation” briefly introduces the advantages and benefits of using dynamic multi-volume hourly passive thermal simulation of a dwelling and makes particularly refers to AccuRateNZ. AccuRateNZ was brought to New Zealand (from Australia) in the late 2000s by EECA for government’s ‘NZ Home Energy Rating Scheme’. In my next EBOSS Blog I will explain why I consider that MBIE should dust off the software and make it available to those architects and designers who wish to add this greater depth of analysis to their projects. This would not be part of NZBC-H1, but rather available as an alternative H1/VM path for those who have a need for a more nuanced and comprehensive means of evaluating the energy efficiency of their Proposed residential developments.

In the final count, what matters is that the method/s specified for designing and demonstrating Energy Efficiency compliance should first maximise the ‘free’ passive cooling and heating opportunities offered by the environment before there is a need to introduce resource and energy hungry mechanical equipment. Following from this the construction methods and materials need to be buildable so as to produce long-term liveable settings for the occupants. The 50 year durability requirement of the Building Code is a long time; never mind that the current new dwellings will continue to be around for many decades afterwards.

Do the communities of the future want to have to deal with demolishing Energy Slums?