In this article I look at what is involved in carrying out energy efficiency assessments on buildings in accordance with Section J of Volume 1 of the National Construction Code Series 2012 Volume 1 Class 2 to 9 Buildings.

    All assessors complete a 4 day course, Short Course in Building Thermal Performance (Residential) - Course Code 91318NSW, in order to gain accreditation and practice as assessors in most States and Territories. This qualification provides basic training in the assessment of residential buildings only that does not include the assessment of commercial buildings.

    However, the assessment of commercial buildings is a service marketed and provided by many assessors.

    Who can perform a Section J Assessment?

    Who can carry out an assessment of a commercial building? Is there any training available? Are you required to hold a qualification or accreditation to do this work?

    Anyone can do a Section J assessment.

    Assessors who offer Section J assessments often hold formal qualifications in architecture, engineering or building design in addition to the short course qualification in Building Thermal Performance as well as many years of experience in commercial buildings construction. There is little formal training available and you do not have to hold a specific qualification or be accredited in this work to practice.

    The building certifier or local authority for the project takes responsibility for the assessment as part of their roles. The assessor who prepared the Section J assessment may not be legally responsible for work performed but the Certifier or local authority will consider the assessor to be an “expert” in this area as they are an “accredited assessor” even if they do not hold formal qualifications or are accredited to carry out commercial building assessments.

    Therefore, care must be taken if you offer Section J assessments to your clients.

    Under State and Territory Fair Trading legislation, you are considered to be a professional or competent person by offering assessment services on commercial buildings. If an error is made in the Section J assessment that causes a financial loss by one of the project’s stakeholders somewhere in the future, you may be liable if they seek to recover these costs. Yes, the Certifier or local authority is initially responsible but insurers today look to involve any related parties and spread the claim and costs over as many parties as possible. You risk being dragged into a protracted legal case even if not directly involved. The risks are much higher on commercial projects than for residential ones.

    If you offer Section J assessments for commercial buildings, ensure your Professional Indemnity insurance provides adequate cover for this specialist work and that you possess the knowledge and expertise to provide these services.

    What options are available?

    Below  we look at buildings that require assessment under Section J and what options are available to assessors to demonstrate compliance.

    Volume 1 of the BCA lists the requirements that commercial buildings are required to comply with including energy efficiency requirements.

    All building types are classified in the BCA and commercial buildings are considered to be buildings in classes 3 – 9.

    How are they defined?

    Class 3


    A residential building that is not a Class 1 or 2 building (house or unit) such as a boarding house, motel room or the like.

    Class 4


    A dwelling in a building of another class - caretaker's flat (may be assessed using NatHERS tools)

    Class 5


    An office building or the like

    Class 6


    A shop, restaurant or the like

    Class 7


    A car park, a warehouse or building used to wholesale goods

    Class 8


    A laboratory, factory or the like

    Class 9


    Public buildings - hospitals, school buildings, aged care buildings or the like

    The above descriptions are broad and assessors should check the definitions in Part A3 of the BCA for accurate definitions.

    Assessors have two methods available to them to demonstrate compliance with Section J of the BCA – use a Deemed-to-Satisfy (DTS) approach or rate the building using software under the JV3 provisions. Unless suitably qualified and trained in the tools (different to NatHERS tools) assessors generally will assess simple commercial buildings using the DTS provisions of Section J of the BCA.

    It is not permitted under the regulations for commercial buildings to be assessed using residential rating software tools like FirstRate or Bers Pro (excluding a Class 4).

    Section J Parts

    Part J1


    Building Fabric

    The building envelope must meet minimum total R-Value requirements

    Part J2



    Aggregate air-conditioning value attributable to glazing must not exceed nominated allowances

    Part J3


    Building Sealing

    Sealing requirements for chimneys, flues, exhaust fans, building elements, windows and doors

    Part J4


    Not applicable

    Part J5


    Air-conditioning and Ventilation Systems

    Requirements for air-conditioning and ventilation systems

    Part J6


    Artificial Lighting and Power

    Requirements for lighting and power energy consumption

    Part J7


    Hot Water Supply and Swimming Pool and Spa Pool Plant

    Minimum requirements for hot water systems, swimming pools and spas

    Part J8


    Access for Maintenance and Facilities for Monitoring

    Maintenance requirements and monitoring of energy consumption for larger buildings

    All of the above parts must be considered when assessing a commercial building and included in the assessment report if applicable.

    Care must be taken when deciding which method to use to assess a commercial building under Section J. Larger and more complex commercial buildings or those with large areas of glazing such as a car showroom may not be suitable to be assessed using DTS as they exceed the boundaries of the BCA and can only be assessed using JV3.

    Part J1.2 Thermal Construction - General

    It is a requirement of the BCA that insulation products used in a building comply with AS/NZS 4859.1 and installed correctly. Reflective insulation must be installed in a way that maintains airspaces to achieve required R-Values, are closefitting, adequately supported, lapped and taped together. Bulk insulation products must be installed so that it attains its position and thickness.

    It is usual for the assessment report to refer to this clause. It is the responsibility of the builder and the Certifier to ensure the building complies with this requirement.

    Part J1.3 Roof and Ceiling Construction

    To demonstrate compliance, the assessor report must show that the roof/ceiling building meets or exceeds the minimum total R-Value specified in Table J1.3a for a particular BCA Climate Zone. The minimum required R-Value varies according to the BCA climate zone and roof colour.


    200m2 office building located in Shepparton – BCA Climate Zone 4.

    Roof colour – Colorbond Surfmist (solar absorptance – 0.32),

    Table J1.3a – minimum Total R-Value required – R3.2 downwards



    External air film                                                 - 0.04     (7 m/s)

    Metal roof sheeting (20 deg pitch)               - 0

    Air gap (40mm unventilated)                         - 0.33     Downwards (0.9/0.4)

    Sarking (reflective foil facing down)              - 0

    Reflective airspace (unventilated)                 - 0.92     Downwards - BCA Spec J1.2 Table 2c

    Ceiling insulation – R2.5 bulk insulation       - 2.5

    10mm plasterboard ceiling                            - 0.06

    Internal air film resistance                             - 0.16     Still air

    TOTAL                                                                  - 4.01


    This example exceeds the minimum requirement by R0.81 and therefore complies.

    If the roof colour was changed by the client to Colorbond Pale Eucalypt (solar absorptance – 0.6) the minimum total R-Value requirement increases to R3.7.

    The above example complies.

    If the roof colour was changed by the client to Colorbond Cottage Green (solar absorptance – 0.75 the minimum total R-Value requirement increases to R4.2.

    The above example does not comply and the ceiling insulation would need to be increased to R3.0 to meet the minimum requirements.

    Adjustment of Ceiling Insulation for Loss Due to Penetrations

    It is important that the assessment comply with the requirements of Part J1.3 (c) – Adjustment of Minimum R-Value for Loss of Ceiling Insulation where the average R-Value of the ceiling insulation is increased to offset “holes” in the insulation fabric where insulation is required to be kept away from light fittings, exhaust fans and the like to meet fire and safety regulations.

    The above example includes R2.5 ceiling insulation. The lighting design for the office includes 20 halogen down lights and a further calculation would need to be carried out as part of the assessment to determine if the R2.5 ceiling insulation needs to be increased in value to offset the losses due to the down lights.


    Halogen down light – loss of 0.203 m2 per down light (NatHERS Technical Note 2)

    20 x 0.203 m2 = 4.06m2 loss

    4.06 m2 ÷ 200 m2 = 2.03% loss

    Referring to Table J1.3b, the minimum R2.5 insulation must be increased to R3.3 to compensate for the loss due to the inclusion of the down lights.

    It makes a significant difference to the R-Value of the insulation that is required to be installed in the building.

    Thermal Break

    If the project has steel roof/ceiling framing with roof sheeting and ceiling lings directly fixed to the framing members, a note should be included in the assessment report for a thermal break of minimum R0.2 to be provided to underside of the roof sheeting in accordance with Part j1.3 (d).

    Part J1.4 Roof Lights

    Roof Lights are defined in the BCA as a – “skylight, window or the like installed in a roof – (a) to permit natural light to enter the room below; and (b)  at an angle between 0 and 70 degrees measured from the horizontal plane”.

    Glazing in a building that is located in a wall that is between 70 degrees and vertical is considered a window as defined in the BCA.

    Both Volume 1 & 2 of the BCA treat Roof Lights in a similar manner.

    The BCA determines the properties of the Roof Light in a similar manner to those of a window in an external wall. The properties defined are the U-Value and SHGC of the Roof Light. The values used are AFRC values.

    A Roof Light is sometimes required to be located in an internal room to provide ventilation under the BCA. If a Roof Light is required under these provisions, it must not have an area greater than 150% of the minimum area required for ventilation and have a U-Value of not more than 2.9 and a SHGC of not more than 0.29.

    All other Roof Lights must comply with the relevant Table and not exceed 3% of the total floor area of each storey and have a maximum area (expressed as a percentage of the floor area of the room it serves) of 5%. Note that some States have additional requirements in these cases that need to be checked when designing an internal space to include a Roof Light.

    Table J1.4 (BCA Volume 1) shown below lists the maximum values for a Roof Light that are linked to the size and area of the Roof Light as a percentage of the room or space where it is located. In general terms, the smaller the Roof Light, less stringent U-Values and SHGC values apply, the larger the area of Roof Light, more stringent values apply.

    To determine the properties of a Roof Light the following steps should be followed.

    1. Determine the Roof Light shaft index
    2. Determine the area of the Roof Light serving the room as a percentage of the floor area of the room.
    3. Look up the maximum U-Value and SHGC for the Roof Light from Table J1.4 (Volume 1) or Table (Volume 2).


    An internal laundry of 6 m2 includes a 300 diameter tubular Roof Light with a diffuser at ceiling level.

    Step 1 - determine the Roof Light shaft index. The drawings show a vertical rise in the centre of the Roof Light from the ceiling to the roof covering as being 800mm high.

    The Roof Light shaft index is calculated:  0.8 / 0.3 = 2.67

    Step 2 - determine the area of the Roof Light as a percentage of the floor area –

                    Area of Roof Light: Area of a circle (πr2) = 3.1415 x (0.152) = 0.071 m2

                    Percentage of floor area: 0.071 / 6 = 1.2%

    Step 3 – Look up maximum U-Value and SHGC

    The Roof Light installed must have a maximum U-Value of 8.5 and SHGC of 0.83

    Assessors should check with manufacturers for details on the proposed Roof Light to ensure compliance.

    Examples of typical U-Vales & SHGC values for different types of Roof Lights are listed in the BCA for guidance, both with and without a diffuser. The Tables below are found in BCA Volume 2.




    Return to articles