NCC Deemed-to-Satisfy vs Performance Solution

What it is

The National Construction Code (NCC) is a performance-based code. Every part of a building has to meet a Performance Requirement. The NCC gives you two compliance pathways to get there. The first is Deemed-to-Satisfy (DTS), the prescriptive recipe. The second is a Performance Solution, an alternative that you prove meets the Performance Requirement using one of four Assessment Methods.

For residential builders in AU, most Class 1 homes are built entirely to DTS. Performance Solutions show up when a site, design or product sits outside the DTS recipe and you still need to satisfy the certifier.

The two compliance pathways

Deemed-to-Satisfy provisions

DTS provisions are the prescriptive route. Follow the dimensions, materials, tables and referenced standards in NCC Volume Two for Class 1 and 10 buildings, and the build is automatically taken to meet the relevant Performance Requirement. No further proof is needed beyond evidence that products and methods match what the DTS calls up.

Examples that show up on a typical residential job:

• Stud spacing and bracing tables in AS 1684 (timber framing) called up by the DTS
• AS 3740 for wet area waterproofing
• AS 3959 for bushfire-prone areas
• Minimum room sizes and ceiling heights in NCC Volume Two

Performance Solutions

A Performance Solution is anything that does not follow the DTS recipe but still meets the Performance Requirement. You design it, you document why it works, then the building surveyor or certifier accepts it before construction.

Typical residential triggers for a Performance Solution:

• A staircase or balustrade that cannot meet the DTS geometry on a narrow renovation site
• An alternative wall system or facade product the DTS does not list
• A reduced setback or boundary condition where fire separation needs another approach
• A heritage overlay that prevents standard DTS detailing

The four NCC Assessment Methods

The Performance Solution must be proved using one or more Assessment Methods set out in the NCC's general requirements:

1. Evidence of Suitability. Documentary evidence that a material, form of construction or design meets the Performance Requirement or a DTS provision. Think CodeMark certificates, test reports from accredited labs, current product technical statements.
2. Verification Methods. Tests, inspections, calculations or other methods named in the NCC itself that determine whether a Solution complies. Energy efficiency verification methods are a common residential example.
3. Comparison with the DTS Provisions. Show the proposed Solution complies in an equivalent or superior way to the DTS Provisions. The classic worked example is using a thicker wall or a different fire-rated system that performs as well as the DTS recipe.
4. Expert Judgement. The judgement of a person with the qualifications and experience to determine compliance. Usually a fire engineer, structural engineer or accredited consultant.

You can combine these. A Performance Solution for a non-DTS facade product, for example, often uses Evidence of Suitability for the material plus Expert Judgement on installation.

Documentation a residential builder needs

A Performance Solution lives or dies on paperwork. The Performance-Based Design Brief (PBDB) is the starting point on anything non-trivial. Then the certifier or relevant building surveyor needs:

• The Performance Requirement(s) being addressed
• The Assessment Method(s) being used
• Test reports, calculations and engineer's letters
• The final Performance Solution Report
• Sign-off before the work is covered up

NSW, VIC, QLD and the other states each have their own certifier framework, but the NCC compliance logic is national. A Performance Solution accepted in VIC under the building surveyor pathway works on the same NCC framework as a Construction Certificate Performance Solution in NSW.

Where builders get caught

The three failure modes we see on residential jobs:

• Treating a Performance Solution as a verbal agreement with the certifier. Without a written Performance Solution Report, the work is non-compliant.
• Using a DTS provision and then varying it on site without realising the variation makes it a Performance Solution. Any departure from DTS dimensions or materials triggers the Performance Solution pathway.
• Confusing "engineer signed it" with a complete Performance Solution. Expert Judgement is one Assessment Method. It still needs to be framed against a specific Performance Requirement and documented.

Practical takeaway

If a residential build follows the NCC recipe, stay in DTS. The paperwork is light and the certifier signs off on prescriptive evidence. The moment a design choice steps outside that recipe, you are in Performance Solution territory and the cost of getting it right is documenting an Assessment Method, getting the certifier's written agreement, and keeping the records on file with the build.