> For the complete documentation index, see [llms.txt](https://docs.betterbuilding.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.betterbuilding.io/sign-up-and-plans/news-and-updates/2026/ncc-2025-update-j1v3-verification-using-a-reference-building.md).
# NCC 2025 Update: J1V3 Verification Using a Reference Building
As part of our NCC 2025 development process, we have put a handful of questions to the ABCB that are still waiting for answers.
The silence however has had a useful side effect. It has forced the team to reimagine our reference building workflow, which will now also automate/semi-automate services (HVAC, fans, pumps, etc) when we launch.
Yes, lots more work but the value of this approach means wider benefits in building performance, so we are all in. More info later on this next month.
While initially aiming for a September launch, radio silence from the ABCB and the increased scope now means we are likely to **launch in January 27**.
### Is the fabric first J1V3 method over?
J1V3(1)(a) has always had two parts which i believe we will now need to cover both...
(i) models the proposed building with its proposed services and asks for annual greenhouse gas emissions not more than 97% of the reference building's. That is the new 3% margin, and what many folk have picked up on.
***... the annual greenhouse gas emissions of the proposed building are not more than 97% of the annual greenhouse gas emissions of a reference building when the proposed building is modelled with the proposed services; and***
(ii) is very tricky to read for me. It models the proposed building with the same services as the reference building and asks that the emissions of those services be no more than the emissions of the reference building's services.
***... the annual greenhouse gas emissions of the services of the proposed building are not more than the annual greenhouse gas emissions of the services of the reference building when the proposed building is modelled with the same services as the reference building;***
So, we only need to report on specific services GHG's and have identical plant on both sides as per the reference building requirements, so the only thing left that can differ is the fabric?
This is business as usual for many today. Your envelope has to do at least as well as the reference envelope, with the reference plant serving both. But there is a slight rub. The reference envelope has also got tighter or more onerous on the cooling side of the equation.
The maximum reference solar admittance for Class 5 to 9b buildings has dropped from 0.13 on every aspect to 0.09 north and west, 0.10 east and 0.11 south across climate zones 1 to 7, and the wall-glazing U-Value limits are now set per climate zone **i**nstead of a flat U2.0. You can check the numbes yourself below.
Because the reference glazing SHGC is simply the solar admittance limit divided by the glazing share, it gets tighter the more glass you have. A north facade in climate zone 5 gets a reference SHGC of about 0.25 at a 36% window-to-wall ratio, 0.18 at 50% and 0.15 at 60%. Under NCC 2022 those same facades sat at 0.36, 0.26 and 0.22. If you are in a cooling dominated climate with more than 40 or 50% glazing, the building you are measured against now carries seriously good glazing systems with assumed high solar control
So the strategy appears to be two fold. You must first comply with your services (i) (if you want to use the full J1V3 pathway that is) and then the fabric (ii) (if you are complying with the services via the DtS provisions or other method). The reference building fabric is more onerous, and you get little benefit from offsetting GHG's with PV now as PV is in your reference building.
### PMV, but mostly zone sizing
The PMV route in J1V3(1)(b) applied to every class under NCC 2022. It is now confined to Class 5.
The other four routes are open to every class, offices included... There is a dry bulb route, 18 °C to 25 °C degrees in transitory spaces and 21 °C to 24 °C elsewhere, held across 95% of the floor area for 95% of the annual hours of operation, and three climate zone based load routes. The zone load routes drag in the newly formed Specification 48, and this is likely the place I will lose a few readers.
***... a zone of the proposed building is assessable under J1V3(1)(b)(iii) to (v) if it has — a 98th percentile heating load of at least 10 W/m2: or a 98th percentile cooling load of at least 40 W/m2.***
The 10 W/m2 heating and 40 W/m2 cooling figures in S48C2(3) are not targets. They are a screening threshold. A zone is assessable if its 98th percentile heating load reaches 10 W/m2 or its 98th percentile cooling load reaches 40 W/m2, and zones below both simply drop out of the comparison.
The test itself lives back in J1V3(1)(b)(iii) to (v): the proposed zone's 98th percentile load must not exceed 110% of the corresponding reference zone's (cooling in zone 1, heating in zone 8), or 120% for both loads in zones 2 to 7, across 95% of the assessable floor area. Not every zone, 95% of the assessable area.
Practically it is a painful processing exercise in both reference and proposed designs. Per-zone hourly sensible loads out of both models, the S34C3(8) temperature bands applied, percentiles formed, compared. What Specification 48 does not tell you is how to form the percentile, over which set of hours, or on what area basis. Its also unclear what happens when the reference building doesn't pass.
### Future climate files, but plant sized for today?
S34C3(1)(d) requires both buildings to be modelled with climatic data from a projection at year 2050 under RCP 8.5.
***... climatic data, using a projection at year 2050 made under a Representative Concentration Pathway with an 8.5 W/m² increase in radiative forcing;***
No source is named, nor is a method given for producing the file. Expectation appears to be that we all use one of the 83 files from [CSIRO files](https://agdatashop.csiro.au/future-climate-predictive-weather) it seems.
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However, we also need to consider that we also now need to undertake plant sizing in Specification 48. S34C4 requires part load, staging and capacity regulation to be modelled, which means the reference plant has to be sized from something, and nothing in Specification 34 or 48 says whether that something is the projected file or current design data.
For now the defensible approach would appear to size from current design conditions (not future, as we don't have a method), and then run the annual simulation on the projected file. Messy, i know.
### A reference building with solar
This is the bit that makes my head hurt a little.
Under S34C2(a)(iii) the reference building carries its own PV system, by one of two routes, and the text does not say which. The choice is yours.
***... be provided with a solar photovoltaic system that complies with — J9D5(2)(a), J9D5(3) and J9D5(4) with PV panels modelled as parallel to the roof and assuming an average solar photovoltaic panel power rating of 225 W/m2; or J9D5(2)(b), J9D5(3) and J9D5(4).***
Route J9D5(2)(a) applies a 100% of the roof area less the eleven exclusions (shaded areas, pitch over 45 degrees, awnings, car parks, roof gardens, terraces, roof lights, access and plant areas, heat rejection exhaust, anywhere impractical), modelled parallel to the roof at an average 225 W/m2.
Most of those exclusions are settled late in design, so for most of the time you are modelling, the eligible area is a guess. It is not clear if this is actually useable and appears to reference a lack of understanding regarding when such info is available in the design process.
Route J9D5(2)(b) applies a peak output per m2 of conditioned space, which is 65 W/m2 for a Class 5, 6 or 7 building in zones 2 to 7. The reference table is titled "for buildings WITHOUT gas", and that heading me down a rabbit hole as the first pathway (J9D5(2)(a)) appeared to be WITH gas? Just a type or have i missed something?
To keep this short, it appears that the determination of the reference building PV contribution is open to wide interpretation and of course, reference building manipulation. If you can use it to 'control' the influence on reference building green house gas outcomes, that is what the market will do. It doesn't appear to add value, appearing to create a convoluted theoretical process at the minimum that will set up conversation of how did you reach those numbers until greater clarity is provided.
### Contact the ABCB
For folks interested in this space, i strongly recommend a deep dive into the trials and potential tribulations of the future application of NCC 2025 J1V3. While the Better Building team and i have many years of experience in this space, we cannot answer questions on interpretation and can only recommend you reach out to the ABCB for more direct support.
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