NCC 2019 changes to Section J; thermal performance, condensation and building design

2 August 2021 Kingspan Insulation Australia

The National Construction Code 2019 introduced significant code changes to Section J to help buildings in Australia improve energy productivity by 40% by 2030. It is important to understand these changes and the impact they will have when designing the best building for your needs.

Condensation mould

To help you fully understand the topic, it is best to start with how insulation works. Heat moves from a warm space to a cooler one. This movement is what causes buildings to get warmer in the summer and cooler in winter. The use of insulation helps to mitigate this movement by; stopping heat moving through the building in summer and restricts heat leaving the building in winter. To learn more about the basics of insulation, read our Insulation 101 article.

NCC 2019 Code Changes to Section J

As buildings use a lot of energy, the National Energy Productivity Plan (NEPP) was introduced to improve Australia’s energy productivity by 40% between 2015 and 2030. Part of the NEPP was to develop and improve National Construction Code (NCC) requirements by; improving the codes readability, increasing the severity of the energy efficiency provisions and quantifying against the performance based code directly or by the development of verification methods.

Facade U value

J1.5 – Façade U-value

One of the biggest changes in NCC 2019 was the introduction of new benchmarks and notions regarding minimum performance requirements for wall and glazing components of a wall-glazing construction. Using an area-weighted average between the wall area and glazing area, combined a walls façade must have a maximum U-value of 2.0 for most buildings and climate zones.

The wall components of a wall-glazing construction must achieve a minimum total R-Value of Rt1.0 where the wall is less than 80% of the WGC and Rt1.4 where the wall is more than 80% of the WGC.

AS4859.1:2018 and AS4859.2:2018

Another change in NCC 2019 that had a significant impact was a reference to AS4859.1:2018 and AS4859.2:2018. The AS4859.1:2018 release introduced changes to the way a product is tested and how a materials thermal performance (R-value) is determined and declared. Where AS/NZS 4859.2:2018 represents a prescribed procedure for calculating the overall thermal resistance of the construction assembly, including a new reference to the New Zealand standard, NZS4214:2006 when calculating the effect of thermal bridging.

Total R-value

The definition of total R-value also changed in NCC 2019. Total R-value, for the purposes of Volume One, is now defined as the sum of the R-values of the individual component layers in a composite element including any building material, insulating material, airspace, thermal bridging and associated surface resistance. The main difference between NCC 2016 and NCC 2019 definition is the inclusion of thermal bridging.
Thermal bridging now needs to be accounted for within thermal calculations and design. NCC 2019 has adopted an Isothermal Plane Method to determine total R-value. An Isothermal Plane Method breaks the components in an assembly into two types: (i) a component which has parallel paths of heat flow (ie; glasswood in between steel studs), and (ii) continuous layers of homogeneous materials which are included in assembly (ie: plasterboard lining).
This method of calculating a total R-value allows for better accuracy when determining heat transfer thus in turn reducing energy costs, rising emissions and negatives impact upon the thermal comfort of building occupants. Using a continuous layer of insulation will help mitigate thermal bridging, find out more here.

Movement of vapour

Condensation and Mould

Historically condensation within buildings has not been a prominent issue for most of Australia. However, increased thermal performance requirements, airtightness and air-conditioning have brought condensation to the forefront of the discussion. Condensation is defined as water vapour in the air that condenses from a gas into a liquid form.

Condensation management is also referenced in Part 6 of NCC 2019. Part 6 was introduced to minimise the risks associated with water vapour and condensation, ensuring they are managed to reduce their impact on the health of building occupants. 
There are several common causes of moisture in buildings that can lead to condensation and damp problems; ground moisture, rainwater, flooding, construction moisture and moisture generated by occupants. If condensation issues are not addressed, it can lead to health problems for building occupants, rotting structures along with lowering the thermal performance of your insulation.
To manage condensation when designing and planning a building it is important to select a compliant insulation that is suitable for the climate zone, ensure the building is well ventilated and consider using continuous insulation.
With the codes changes to Section J of National Construction Code 2019 now covered along with helping you gain a much greater understanding of thermal bridging and condensation management, please feel free to reach out to our Technical Services team on 1300 247 235 or email with any enquires or concerns you may have about your next project.

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Kingspan Digital Academy Courses

As of a result of the changes in code made to Section J of NCC 2019, understanding Total R-values has become extremely important. 

In this course we take a look at the very fundamental purpose of building insulation and its importance for the built environment as well as the future of sustainability for the planet. The many advantages of using insulation and the disadvantages of not using it in buildings may surprise you.

By the end of this course you will: 

  • Understand the basic purpose of insulation
  • Understand how adding insulation into a building design affects building performance and comfort for occupants
  • Understand the importance of insulation for sustainable buildings
  • Understand the major disadvantages of un-insulated buildings for building performance, the occupants and the environment