Understanding Specification 44: A Practical Guide to NCC 2022 Thermal Performance

Following recent inquiries and discussions sparked by the release of our dedicated Specification 44 workflow, we've prepared this comprehensive guide to address common questions and concerns about this new first-principles approach to NCC 2022 residential compliance.

Our objective is to clearly explain the why, what, and how of Specification 44, clarifying its intent and limitations while providing practical guidance for its application in real-world projects.

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Why Does Specification 44 Even Exists?

You might wonder why Specification 44 was developed, especially given that DTS provisions have become significantly more challenging to apply under NCC 2022 and the significant focus on NatHERS 7-stars. This concern is understandable and deserves explanation.

The root of Specification 44 existence lies in how NCC 2019 handled Performance Requirements for housing energy efficiency. These were written in qualitative and subjective terms, creating significant interpretation challenges for practitioners who struggled to determine exactly what was required and how to demonstrate compliance effectively. This ambiguity also allowed certain practitioners to deliver poor outcomes to homeowners, particularly in South and Western Australia. All while flying the banner of sustainability!! The result was inconsistent assessments, made up DTS provisions and ongoing disputes over what constituted adequate thermal performance.

Recognising these issues, the Australian Building Codes Board determined that NCC 2022 needed quantified, measurable standards to eliminate ambiguity. This new approach establishes specific numerical targets that buildings must meet while maintaining the same overall performance level of 7-star equivalent energy efficiency.

Specification 44 emerged as the technical solution to address these challenges. Instead of subjective assessments, practitioners now have detailed calculation methods for determining maximum allowable heating loads, cooling loads, and total thermal energy loads. This provides the mathematical framework needed to definitively determine whether a building meets the thermal performance requirements under H6P1.

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What is Specification 44?

Specification 44 comprises three interconnected calculation methods that work together to define thermal performance limits deemed equivalent to 7-star NatHERS performance. However, it's crucial to understand that any relationship with NatHERS ends there. Specification 44 uses different simulation engines, internal areas, internal loads, and climate files, which means outputs cannot and should not be compared with NatHERS results, even when using the same units. Here comes the technical bit.

S44C2 - Heating Load Limit (HLL): This calculation determines the maximum permissible annual heating energy for a building. The formula takes the greater of either 4 MJ/m².annum (baseline value) or ((0.0044 x HDH) – 5.9) x FH (climate-adjusted calculation). The formula incorporates heating degree hours (HDH) specific to the building's location and an area adjustment factor (FH) derived from lookup tables based on total habitable room area. This approach ensures buildings in colder climates receive appropriate heating load allowances while maintaining consistent performance standards.

S44C3 - Cooling Load Limit (CLL): The cooling calculation reflects the complex nature of cooling loads across Australia's diverse climate zones. The formula CLL = (5.4 + 0.00617 × (CDH + 1.85DGH)) × FC incorporates cooling degree hours (CDH), dehumidification gram hours (DGH), and an area adjustment factor (FC). This accounts for both sensible cooling (temperature control) and latent cooling (humidity control), making it particularly relevant for Australia's hot, humid northern regions.

S44C4 - Thermal Energy Load Limit (TLL): This represents the most comprehensive calculation, combining heating and cooling considerations into a single thermal energy budget. The formula TLL = 19.3HLL + 22.6CLL − 8.4 − 15/(Tr + 10.74) incorporates the previously calculated heating and cooling limits along with the annual average daily outdoor temperature range (Tr). This creates a holistic thermal performance envelope that reflects the total energy requirements of the building.

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How you Apply Specification 44 in Practice?

The primary application of Specification 44 is in developing first principles Performance Solutions, where you demonstrate compliance with H6P1 through direct assessment against the Performance Requirements. This approach offers maximum design flexibility but requires thorough understanding of both the technical calculations and the Performance Solution development process. In other words, you need to know what you are doing!

When using this pathway, you function as the thermal performance assessor, calculating whether your specific building design meets the heating, cooling, and thermal energy load limits. With appropriate upskilling, registered NatHERS Cert IV assessors are ideally positioned to deliver Specification 44 assessments, given their existing familiarity with Class 1 assessments.

This process itself can involve gathering local climate data, determining your building's thermal characteristics, and conducting detailed thermal modelling to predict actual loads. You then compare these predicted loads against the Specification 44 limits to demonstrate compliance.

This approach proves particularly valuable for building designs that don't align well with standard compliance pathways. Whether you're designing homes with unconventional materials or earth-coupled thermal systems, a first principles approach using Specification 44 allows you to demonstrate that these innovations achieve required thermal performance without being constrained by prescriptive requirements. However, it needs to be clear that it is not limited to unconventional designs and can be used for standard homes.

When developing a Performance Solution using Specification 44, the specification becomes central to your Performance-Based Design Brief (PBDB). The PBDB must establish clear acceptance criteria, and Specification 44 provides the quantified benchmarks that form these criteria.

Your PBDB would typically state that the proposed design will achieve heating loads not exceeding the Specification 44 heating load limit, cooling loads not exceeding the cooling load limit, and thermal energy loads not exceeding the thermal energy load limit for the specific climate and building size. This creates clear, measurable targets that all project stakeholders can understand and building surveyors can objectively assess.

However, it's important to remember that while Specification 44 addresses H6P1 thermal performance requirements, you must also satisfy H6P2 energy usage requirements. Thermal performance represents only one component of the overall energy efficiency compliance framework.

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Do I Need Specification 44 Training?

While commercial ESD engineers and consultants are generally skilled in more complex energy modelling, registered NatHERS Cert IV assessors may need to upskill to fill in knowledge gaps to consider using Specification 44.

To bridge the knowledge gap, Better Building are providing free training to registered NatHERS Cert IV assessors and offer project reviews to ensure your next project provides a robust and compliant solution for the National Construction Code. Better Building are currently seeking a partnership with a third party to provide a review service for Specification 44 models.