NCC 2025: Heading Towards Net Zero in Commercial Buildings

The new changes in Section J of NCC 2025 aim to push commercial buildings towards the 2050 net-zero goal. The major changes in requirements for non-residential buildings can be summarized as:

• Solar PV Mandate: Solar PV systems must be installed for either 100% of the available rooftop area or a substantial portion of it, depending on the facility’s conditioned area.
• Improved Wall-Glazing and Roof/Ceiling Performance: To make commercial buildings more resilient to outdoor conditions, the new NCC 2025 requires improved building fabric compared to NCC 2022. Other than a handful of building classes in certain climate zones, all other non-residential buildings must have more insulation in their building fabric forming the envelope.
• Improved External Glazing Performance: Under NCC 2025, windows will be darker to achieve higher SHGC and require less cooling. There are also broad upgrades to the windows’ U-value across the board for all commercial buildings, with a few exceptions, which will be discussed further.
• Stricter Sealing Requirements: Roof lights, windows, and doors, and exhaust fans that are within the building envelope, serving non-habitable or unconditioned rooms, must also be sealed or capable of being sealed.
• High Efficiency Services: All heating and cooling equipment efficiency requirements (including fans) have been improved to reduce the reliance on the electricity grid and help the industry move towards Net Zero.
• Natural Gas Phase Out: Although the use of gas for space heating and domestic water supply is not prohibited, there are additional requirements for buildings connected to the gas pipework to disincentivise connection to natural gas, such as requirements to install additional electrical alternative capacity for future and additional PV requirements.
• Demand-Controlled Ventilation: For regularly occupied spaces, if suitable, NCC 2025 reduces the threshold by which a building must install a demand-controlled ventilation system to reduce the energy used for ventilation.
• Demand-Operated Control Devices for Lighting: Manual on/off switches are not allowed to be installed in commercial buildings, with a few exceptions. Instead, motion detectors, time switches, and other demand-operated control devices must be installed to control the artificial lighting operation.

Applicability of NCC 2025 Volume 1

• NCC 2025 new changes apply to Classes 3,5,6,7,8 and Class 9 building. In this article, these building classes are referred to as “commercial buildings”.
• NCC 2025 changes do not apply to Apartment, Class 2 building; NCC 2022 Vol 1.0 still applies.
• The residential part of a commercial building, Class 4, has no new significant changes from NCC 2022, but requirements are included and discussed in NCC 2025 Vol 1.0.
• Residential dwellings, Classes 1 and 10, are discussed in NCC 2025 Vol 2.0, which do not change.

NCC 2025 New Performance Requirements

• Commercial buildings shall facilitate near-zero operational greenhouse gas emissions.
• Facilitation of solar radiation, energy source of services and sealing of the envelope are omitted from the statement and are included in the new Performance Requirement for the allowable greenhouse gas emissions (see below).
• NCC 2025 decreases the allowed energy consumption by almost half for all building classes
  • for an office building (Class 6), 40 kJ/m2.hr (NCC 2022: 80 kJ/m2.hr)
  • for a Class 5, 7b, 8 or 9a building other than a ward area, or a Class 9b school, 22 kJ/m2.hr (NCC 2022: 43 kJ/m2.hr)
  • for all other building classifications, 8 kJ/m2.hr (NCC 2022: 15 kJ/m2.hr)
• NCC 2025 introduces a maximum emission rate:
  • for an office building (Class 6), 4 grams of CO2-e/m2.hr
  • for a Class 5, 7b, 8 or 9a building other than a ward area, or a Class 9b school, 2 grams of CO2-e/m2.hr; and
  • for all other building classifications, 1 gram of CO2-e/m2.hr.

JV3 report – Verification Using a Reference Building (J1V3)

• The proposed air conditioning system or HVAC, combined with other building services, shall achieve at least 3% improvement in GHG emissions for the proposed building, compared to a reference building with reference services.
• Similar to NCC 2022, one cannot achieve compliance by the use of higher efficiency proposed air conditioning and HVAC alone. Thermal performance of the proposed building on its own must perform better than the reference building. This is worded as: Proposed building with reference services shall emit less GHG that NCC reference building with reference building (No change from NCC 2022).
• Thermal comfort modelling via the PMV metric is now a requirement only for Class 5 buildings.
• A new rule for compliance has been introduced for the J1V3 assessment called the 98^th percentile rule. The 98^th percentile is simply the required heating or cooling demand in a room that meets 98% of the total annual heating/cooling demand of the room.
• Complying with the 98^th percentile rule means that the proposed building’s thermal performance cannot be too far off the reference building. According to J1V3 (b)(iii) to (v):
  • In Melbourne, Sydney, and all other cities in climate zones 2 to 7, the 98th percentile zone heating and cooling load shall not exceed 120% of that of the reference building, across 95% of the assessable floor area.
  • In the hottest areas, climate zone 1, the 98th percentile zone cooling load shall not exceed 110% of that of the reference building, across 95% of the assessable floor area.
  • In coldest areas, climate zone 8, the 98th percentile zone heating load shall not exceed 110% of that of the reference building, across 95% of the assessable floor area.
  • Minimum 98^th percentile to consider for heating is 10 W/m2 and for cooling is 40 W/m2.
• In NCC 2025, the reference building must have a solar PV system (as per DtS requirements) having a PV power rating of 225 W/m2 for 100% of its available roof area. This was not a requirement under NCC 2022.
• Mandatory solar PV for the reference building makes it harder for the proposed building to offset the poor performance of its fabric or services, by the use of renewables.
• For spaces larger than 20m2, the assessor must separate perimeter zones adjacent to the external façade (within 45° of the cardinal directions) from the central zones. This is required for the better capture of heating or cooling demand adjacent to the exposed surfaces, instead of averaging out the indoor condition across a big area.
• Reduction in the stated kgCO2/GJ emission factors for electricity due to the grid reliance on renewables (example: for Victoria, NCC 2022: 279 kgCO2/GJ; NCC 2025: 135 kgCO2/GJ)
• Change in artificial lighting hourly profiles for Classes 5, 6 and 9b school. For instance, the lighting profile between 12 AM-7 AM and 9 PM-12 AM is reduced from 15% to 0%.
• Change in occupancy hourly profiles for the Class 6 shop and the 9c aged care facility. For instance, the occupancy profile between 1 PM and 5 PM is increased from 15% to 20%.
• Change in air-conditioning hourly profile for Class 9c aged care facility. For instance, the AC profile between 10 AM and 4 PM is changed to “on”.

NCC 2025 new changes to Building Fabric energy compliance requirements

• Roof/ceiling construction
  • The required insulation in the new NCC 2025 depends on building class, as well as climate zone.
  • The required insulation for non-residential accommodation, building classes 3, 9a ward area and 9c, other than in climate zone 5, has been increased by at least 10% for climate zone 8 and at most 50% for climate zone 6.
  • No change in the required roof/ceiling insulation for other building classes.
  • For roof colour, other than the previous solar absorptance requirement, there are two additional thresholds that one can abide by: Total Solar Reflectance of at least 0.55, and Solar Reflectance Index (SRI) of at least 61.
  • If an air-cooled AC unit is installed close to a metal roof, a light roof colour must be selected: Total Solar Reflectance of at least 0.65, and Solar Reflectance Index (SRI) of at least 80. If it is installed 2m or more above the roof, this does not apply.
• Roof light (no new change in NCC 2025)
• Walls and glazing
  • Façade (wall and glazing) performance requirement is stricter in NCC 2025 for Class 5, 6, 7, 8, 9b building or a Class 9a building other than a ward area, by at least 5% and at most 20% across all climate zones, with an exception of climate zone 8, which, no change has occurred (same U2.0 as NCC 2022).
  • For Class 3 or 9c building or a Class 9a ward area, façade performance requirement has improved only for buildings in climate zones 2 and 5, both by 20%. For climate zone 1, the requirement stayed the same as NCC 2022. For other climate zones, the façade performance requirement is reduced by at least 9% (climate zone 7) and at most 45% (climate zone 6).
  • The required wall insulation for façades with a low glazing ratio (lower than 20%) has been increased for all building classes in climate zone 1 by at least 20%. For Class 5, 6, 7, 8, 9b building or a Class 9a building other than a ward area, the required wall insulation has been increased for climate zone 3,4,7 and 8 by at least 43% (for climate zone 4) and at most 157% for climate zone 8.
  • The window tint requirement is increased. Solar admittance into the building across all climate zones and building classes is reduced by at least 9% (southern aspect – CZ 1 to 7) and at most 72% (western aspect of climate zone 8); therefore, the use of tinted windows is encouraged in this standard.
• Floors (no new change in NCC 2025)

In conclusion, the NCC 2025 requires higher roof insulation and performance but poorer façade performance of almost the same amount for building Class 3, 9c or Class 9a ward area. Also, façade performance for other building classes is improved, keeping all the other parts of the building fabric the same as required by the old NCC 2022.

Building Sealing

• Unlike NCC 2022, roof lights serving an unconditioned space or non-habitable rooms, forming the building envelope, must be sealed or capable of being sealed.
• Exhaust fans are required to be fitted with a sealing device, such as a self-closing damper, even if serving an unconditioned space or a non-habitable room.
• NCC 2025 requires that everything be sealed if it is forming part of the building envelope. NCC 2022 was more rigorous and required all windows, doors, ceilings, walls, floors and any opening, such as a window frame, door frame, roof light frame or the like, to minimise air leakage even if not part of the envelope.

Air-conditioning and Ventilation

Air-conditioning System Control

• Airconditioning system that serves more than one zone with heating and cooling requirements at the same time must not have a single heating and a single cooling coil.
• To the maximum extent possible, diverse loads must be met through modulating airflow.
• NCC 2025 places a hard limit on the zone-level reheating and re-cooling by not more than 7.5°, whereas in NCC 2022, the threshold depended on whether the flow rate is fixed or variable.
• NCC 2022 required that fans in an air-conditioning system be variable speed if the supply airflow is more than 1000 L/s. According to NCC 2025, there is no requirement on the basis of airflow, but rather, on the basis of fan power input (see Fans below).
• If the design heated water temperature is less than or equal to 45°C, there is no requirement to make the heated water circuit capable of automatic variable temperature operation (variation depends on the outdoor temperature).
• In case the chiller is water-cooled (i.e., connected to a cooling tower), the cooling tower’s outlet (chiller’s inlet) must be capable of variable temperature operation (variation depends on the outdoor temperature).
• There are also requirements for pre-programming of an AC system’s time switch. For instance, the time switch must be programmed to turn off for public holidays 1 year ahead.
• Total airflow requiring an economy cycle changed for climate zones 6 and 8, by 40% and 50,% respectively. For instance, in climate zone 6, instead of 2000 L/s, an AC system having a total airflow of 1200 L/s is required to have an economy cycle configured for its operation.