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The NCC Performance Requirements can be met using either a Performance Solution, Deemed-to-Satisfy (DTS) Solution, or a combination of both. 

The following is a general representation and introduction to the DTS Provisions for waterproofing in Class 1 buildings (houses). The NCC 2022 waterproofing provisions in Volume Two, aim to safeguard the occupants from illness or injury and protect the building from damage caused by the accumulation of internal moisture arising from the use of wet areas in a building. 

The waterproofing provisions in NCC Volume Two require a building to be constructed in a way that prevents potential health risk, dangerous conditions or any damage to building elements which can caused by dampness or waterflow from wet areas such as bathrooms, laundries or the like in a building.

The information presented provides a national overview of the NCC and does not contain any state or territory variations. For further information about floor waste requirements in Queensland, please refer to Newsflash 622.

Before we start outlining the NCC 2022 requirements for wet areas, it is important to provide some background to the history of the wet area requirements. 

The first edition of NCC Volume Two was issued in 1996, and that edition had construction details for wet areas. In NCC 2012, it was decided to remove construction details from Volume Two. This meant Volume Two set out what needed to be waterproofed or made water resistant – and then you had to go to Australian Standard (AS) 3740 Waterproofing of domestic wet areas for construction details. In summary from 2012 to 2019, the NCC told us what to do, and AS 3740 told us how to do it.

Fast forward to NCC 2022 and a review of the wet area provisions resulted in a decision to reinstate the construction details back into code itself, with the option to choose AS 3740 for a construction solution if desired. 

In addition, NCC 2022 introduced changes to clause numbering due to the introduction of a consistent volume structure (CVS) across all 3 volumes of the NCC and with it, the introduction of the ABCB Housing Provisions Standard (Housing Provisions).

The requirements for wet areas in NCC 2022 are in:

• Volume Two, Part H4 Health and amenity, 
• the Housing Provisions, Part 10.2 Wet area waterproofing, and
• AS 3740 (depending which option you use).

Let’s unpack this further.

H4P1 is the only Performance Requirement for wet areas in Class 1 buildings (houses).

H4D2 and H4D3 are the relevant DTS Provisions for wet areas in Volume Two. H4D2 sets out where protection is required for wet areas and H4D3 (new for 2022) sets out what materials must be used and how they must be installed. 

Together, these 2 DTS Provisions outline 2 compliance options to meet H4P1. These options are outlined in the figure below.

This means the available options and where they are located is as follows: 

• Option 1: Use of the Housing Provisions only – Part 10.2 in full (i.e., 10.2.1 to 10.2.32)
• Option 2: Use of the Housing Provisions (10.2.1 to 10.2.6 and 10.2.12) and AS 3740.

Next let’s have a look at these requirements in more detail.

In short, the actual technical requirements to tell us what needed to be waterproofed or made water resistant have not changed very much compared to NCC 2019, but they look different as they are no longer contained in tables.

Clauses 10.2.1 to 10.2.5 closely replicate the requirements contained in Table 3.8.1.1 from NCC 2019, with an additional clause to cover waterproofing requirements for toilets with a bidet spray, refer 10.2.5. There is also a modification to 10.2.2 which now mandates the walls of the shower area to be waterproofed to a height of 1800mm.

Clause 10.2.12 is a new requirement for falls in the Housing Provisions. It isn’t making you install a floor waste. But – if you do put a floor waste in – then the NCC will now require you to grade the floor towards that waste. It’s always been a good idea, but now it’s mandatory in NCC 2022.

We will not go into the details of these clauses (10.2.6 to 10.2.32) and construction details in the Housing Provisions, however, to provide an overview on their inclusions, they are grouped and presented in Figure 2.

• The construction details in the Housing Provisions does refer you to AS 3740 in one place – and that’s for some additional options for bath/wall intersection details.
• If you choose to use the option that includes AS 3740, make sure you use the correct version, AS 3740: 2021. This revised edition is referenced in NCC 2022 and specifies the minimum construction and installation methods to demonstrate compliance.

The NCC Performance Requirements can be met using either a Performance Solution, Deemed-to-Satisfy (DTS) Solution, or a combination of both. The following is a general representation of the DTS Provisions for thermal bridging.

The thermal bridging requirements are contained in the energy efficiency DTS Provisions in NCC Volumes One and Two. This is an introduction to thermal bridging and how the NCC deals with it for commercial buildings in NCC Volume One (Clause J4D3(5)). 

This document explains how to account for thermal bridges when calculating the Total R-Value of certain construction types. It provides a national perspective of the NCC and does not contain any state or territory variations.

Thermal bridging, in practical terms for the NCC, is an unintended path of heat flow between the outside and inside of the building envelope. 

Thermal bridges may occur where there is an interruption in the insulation or where highly conductive materials (e.g. metal) are used.

Thermal bridges can significantly reduce the effectiveness of the insulation (thermal resistance) of the façade by essentially bypassing the insulation in favour of a more conductive material (e.g. metal). This results in either losing heat from inside the building to the outside on a cold day, or adding warmth to the inside the building on a hot day. This may cause unwanted comfort issues in a building, and a likely increase in energy use by a building’s heating and cooling systems.

Additionally, unaddressed thermal bridges may lead to condensation where warm, moist air contacts a colder surface and condenses into water droplets. Condensation can result in mould growth, causing indoor air quality issues, negative health impacts for occupants, and potentially affects the durability of the structure.

The NCC requires thermal bridging to be considered when calculating the Total R-Value/Total System 
U-Value in the following construction types: 

• steel and timber frames in the building envelope
• windows
• spandrel panels.

While the NCC does not prescribe methods for the following construction types, thermal bridging may also occur in:

• junctions between the floor, wall and roof
• penetrations in the building envelope for pipes and cables
• brackets or connection points for external shades or balconies
• slab projections
• steel wall ties used in masonry construction.

Total R-Value and Total System U-Value describe thermal resistance/transmittance (i.e. the ability of heat to transfer through a system or material). These values relate to one another, with the R-Value being the inverse of the U-Value.

Typically, R-Value is used to refer to a material’s ability to prevent heat flow from a cold environment to a warm environment.

Whereas U-Value is used to describe a material's ability to transfer heat from a warm environment to a cold environment.

When using the NCC, R-Value (m².K/W) means the thermal resistance of a component, such as a layer of insulation. It is calculated by dividing its thickness by its thermal conductivity. The Total R-Value (m².K/W) means the sum of the R-Values of the individual component layers in a composite element, such as an external wall. It includes any building material, insulating material, airspace, thermal bridging and associated surface resistances.

When using the NCC, Total System U-Value (W/m².K) means the thermal transmittance of the composite element allowing for the effect of any airspaces, thermal bridging and associated surface resistances. 

To understand what a 'good' or 'bad' value is, the higher the Total R-Value, the better insulator it is, whilst the opposite is true for the Total System U-Value.

While adding more insulation can help to account for thermal bridges, if they are to be truly fixed a thermal break or continuous insulation layer is needed.

A thermal break is an element with low thermal transmittance placed strategically to interrupt the heat flow path through elements with high thermal transmittance. 

Figure 1 provides an example of a thermal break in a spandrel panel. The thermal break is created by using a non-metal structural sealant, weather sealant, gasket and trim, as these have low thermal transmittance. The thermal break interrupts the connection between the inside and outside air through the metal mullion (with high thermal transmittance).

Total R-Values can be calculated with allowances for thermal bridging in accordance with AS/NZS 4859.2:2018 Thermal insulation materials for buildings – Design. 

This Standard comprises of a calculation method (NZS 4214 Methods of determining the total thermal resistance of parts of buildings) that accounts for the impact of thermal bridges on thermal performance.

Examples showing how to calculate Total R-Values with thermal bridges are available separately from the ABCB website.

The NCC Performance Requirements can be met using either a Performance Solution, Deemed-to-Satisfy (DTS) Solution, or a combination of both.

The following is a general representation and introduction to the DTS Provisions for thermal bridging in residential buildings. 

It covers the DTS Provisions for thermal bridging in Class 1 buildings (houses), the sole-occupancy units (SOUs) of Class 2 buildings (apartments) and common areas of Class 2 buildings (apartment buildings). The information presented provides a national overview of the NCC and does not contain any state or territory variations.

Thermal bridging, in practical terms for the NCC, is an unintended path of heat flow between the outside and inside of the building. 

Thermal bridges may occur where there is an interruption in the insulation or where highly conductive materials (e.g. metal) are used.

Thermal bridges can significantly reduce the effectiveness of insulation (thermal resistance) in a house or apartment by essentially bypassing the insulation in favour of a more conductive material (e.g. metal). This results in either losing heat from inside the building to the outside on a cold day, or adding warmth to the inside of the building on a hot day.

This may cause unwanted comfort issues or an increase in energy use by the heating and cooling system.

Additionally, unaddressed thermal bridges may lead to condensation. This can occur when warm, moist air contacts a colder surface and condenses into water droplets. Condensation can result in mould growth, causing indoor air quality issues, negative health impacts for occupants, and potentially affects the durability of the structure.

The NCC 2022 thermal bridging DTS Provisions for residential buildings aim to mitigate thermal bridging in metal-framed walls, roofs, ceilings, and floors. This is to ensure they have a performance level of at least 90 to 95% of their timber-framed counterparts.

The DTS Provisions only apply to repeating metal-framed elements in roofs and ceilings, floors and walls including spandrels. 

To comply with the residential energy efficiency DTS Provisions, you must consider thermal bridging when using metal frames. However, you are not required to consider thermal bridging in timber-framed buildings. The exception to this is when you calculate Total R-Value for external walls of apartment buildings. Importantly, there are different thermal bridging requirements for houses, the common areas of apartment buildings and the SOUs (apartments).

Let’s have a closer look at the thermal bridging requirements for houses, apartments and the common areas of apartment buildings in the NCC.

Thermal bridging in houses

The thermal bridging requirements in Volume Two apply to a Class 1 building (house) and a Class 10a building (non-habitable building such as a garage, shed or carport) with a conditioned space.

Part 13.2 Building fabric of the ABCB Housing Provisions Standard (Housing Provisions) contains the DTS Provisions for thermal bridging. The relevant clauses by building elements are in Table 1.

Roofs and ceilings

Clause 13.2.3(3) of the Housing Provisions prescribes methods for reducing thermal bridging in houses with a metal-framed roof.

The requirements of 13.2.3(3) are different for different roof constructions.

For a pitched roof with a horizontal ceiling, there are 4 compliance options: 

1. Achieve the Total R-Value in Table 13.2.3s, calculated using a method that accounts for the effect of thermal bridging.
2. Increase the R-Value of ceiling insulation between ceiling frames by R0.5 more than the R-Value derived from 13.2.3(1).
3. Add a continuous ceiling insulation layer. 13.2.3 (3)(a)(iii) provides details on the insulation required and the correct methods for its installation.
4. Stacking 2 layers of insulation on top of each other to achieve the required R-Value for ceiling insulation as specified in 13.2.3 (1). See 13.2.3 (3)(a)(iv) for more details on how to install it.

For a flat, skillion or cathedral roof, there are 2 compliance options:

• Achieve the Total R-Value in Table 13.2.3t, calculated using a method that accounts for the effect of thermal bridging.
• Comply with Table 13.2.3u. Table 13.2.3u presents 2 methods to mitigate thermal bridging. These are increasing insulation between roof frame members to a specified minimum R-Value, or adding a continuous layer of insulation with a minimum R-Value as specified in Table 13.2.3u above or below the roof frame members.

External walls

Clause 13.2.5(4) of the Housing Provisions apply to a Class 1 building and prescribes methods for mitigating thermal bridging in external walls with the following construction types:

• Concrete block walls with internal lining fixed to a metal frame.
• Lightweight metal-framed walls.
• Masonry veneer metal-framed walls.

There are 2 options available to mitigate the effects of thermal bridging in external walls. 

The first option is to achieve the applicable Total R-Value in  Table 13.2.5p, Table 13.2.5q or Table13.2.5rcalculated in accordance with AS/NZS 4859.2 Thermal insulation materials for buildings design.

The second option is to mitigate thermal bridging based on the type of wall. For:

• Concrete block walls with internal lining fixed to a metal frame (Table 13.2.5s): the options are either increase insulation to a specified minimum R-Value between wall framing or add a layer of continuous insulation as specified in Table 13.2.5s.
• Lightweight metal-framed walls (Table 13.2.5t): the options are either to install reflective insulation or add a layer of continuous insulation as specified in Table 13.2.5t.
• Masonry veneer metal-framed walls (Table 13.2.5u): the options are either install reflective insulation or add a layer of continuous insulation as specified in Table 13.2.5u.

Floors above unenclosed space or subfloor

Clause 13.2.6(3) of the Housing Provisions prescribes methods for reducing thermal bridging for a building with a metal-framed suspended floor.

There are 3 options available to comply with 13.2.6(3). They are:

1. Achieving the Total R-Value specified in Table13.2.6i calculated using a method that accounts for thermal bridging for a suspended floor above an enclosed subfloor space.
2. Achieving the Total R-Value as specified in Table13.2.6i using AS/NZS 4859.2 for all other floors.
3. Complying with one of the options in Table 13.2.6j. This can be achieved either by increasing insulation between the floor framing to a specified minimum R-Value or by adding a layer of continuous insulation as specified in Table 13.2.6j.

To better understand thermal bridging in houses and how to determine Total R-Value, see the examples in the Housing energy efficiency handbook. 

All the tables mentioned earlier are in the ABCB Housing Provisions, available from the ABCB website.

Thermal bridging in an SOU

The thermal bridging requirements for SOUs (apartments) apply to building elements that are part of the external building fabric.

NCC Volume One, Part J3 Elemental provisions for an SOU of a Class 2 building, contains the DTS Provisions for thermal bridging in certain metal framed roofs and metal and timber framed external walls. These clauses are arranged by building elements in Table 2.

There are no provisions for thermal bridging for SOU floors above a car park, undercroft, or the like in apartment buildings.

Roofs and ceilings

J3D7(3) prescribes methods for mitigating thermal bridging for SOUs (apartments) with a metal-framed roof. The requirements are different for different roof constructions.

The compliance options for a pitched roof with a horizontal ceiling are as follows:

1. Achieve the Total R-Value in Table J3D7s calculated using a method that accounts for the effects of thermal bridging.
2. Increase the R-Value of insulation between the ceiling frames by R0.5 more than the R-Value derived from J3D7(1).
3. Add a continuous ceiling insulation layer. J3D7(3)(a)(iii) provides details on the specification of the insulation and the correct methods for its installation.
4. Achieve the R-Value specified in J3D7(1) by stacking 2 layers of insulation on top of each other. See J3D7(3)(a)(iv) for details on how to install it.

The compliance options for a flat, skillion or cathedral roof are as follows: 

• Achieve the Total R-Value in Table J3D7t calculated using a method that accounts for the effect of thermal bridging.
• Comply with Table J3D7u. This table gives 2 methods to mitigate thermal bridging. You can either increase the insulation between the roof frame members to a specified minimum R-Value or add a layer of continuous insulation as specified in Table J3D7u.

All the tables mentioned here are in Volume One of NCC 2022, available from the ABCB website.

External walls

In Part J3, J3D8 and J3D9 are related to the external walls and wall-glazing construction of SOUs (apartments). J3D8 and J3D9 do not specifically mention thermal bridging but specify a Total R-Value or Total U-Value which must account for thermal bridging.

J3D8(2) requires the Total R-Value to be determined in accordance with Specification 38 for spandrel panels in curtain wall systems, and in accordance with AS/NZS 4859.2 for all other walls.

J3D9(2) requires the Total System U-Value of wall-glazing construction to be calculated in accordance with Specification 37. This requires you to account for thermal bridging when calculating the Total System U-Value.

Specification 37 and 38 are in Volume Two of NCC 2022, available from the ABCB website.

Thermal bridging in the common areas of apartment buildings

The energy efficiency requirements for common areas of a Class 2 building are different to those discussed above for the SOUs (apartments) of a Class 2 building. 

J4D3(5) is the relevant clause for thermal bridging in common areas of apartment buildings and applies to metal and timber framed building envelopes, windows, and spandrel panels.

J4D3(5) requires consideration of thermal bridging when calculating/determining the required Total R-Value and Total System U-Value. These values must be calculated in accordance with:

• AS/NZS 4859.2 for a roof or floor
• Specification 37 for wall-glazing construction 
• Specification 39 or Section 3.5 of Chartered Institution of Building Services Engineers (CIBSE) Guide A for soil or sub-floor spaces.

This is consistent with how the NCC accounts for thermal bridging in commercial buildings.

While adding more insulation can help to compensate for thermal bridges, to truly fix them a thermal break is needed.

A thermal break is an element with low thermal transmittance placed strategically to interrupt the heat flow path through thermal bridges. 

For residential buildings, both Volumes One and Two contain DTS Provisions for thermal breaks in metal-framed houses and apartment buildings. 

These requirements are distinct from the thermal bridging mitigation requirements discussed above. 

The thermal break requirements need to be met in addition to the thermal bridging requirements, where required. 

The clauses for thermal break requirements (by building element) for houses and SOUs (apartments) and the common areas of apartment buildings are in Table 3.

The National Construction Code (NCC) is a performance-based code containing all Performance Requirements for the construction of buildings. To comply with the NCC, a solution must achieve compliance with the Governing Requirements and the Performance Requirements. 

The Governing Requirements are a set of rules outlining how the NCC must be used and the process that must be followed. The Performance Requirements prescribe the minimum necessary requirements for buildings, building elements, and plumbing and drainage systems. The performance-based nature of the code gives you flexibility in how to meet the Performance Requirements. 

This guide will focus on the compliance options for Performance Requirement H6P1 and the development of a first principles Performance Solution using the benchmarks set out in Specification 44.

Housing energy efficiency requirements are in Part H6 of Volume Two in NCC 2022. The overall intent of the housing energy efficiency requirements is to improve the:

• efficient use of energy in housing design and construction, and 

• energy usage by key equipment installed in a building.

The Performance Requirements for housing energy efficiency in Part H6 are:

• H6P1 Thermal performance
• H6P2 Energy use

H6P1 Thermal performance

H6P1 covers the thermal performance of a house’s fabric. It regulates the maximum (or upper limit) of permitted heating loads, cooling loads and total thermal energy loads of homes. See Schedule 1 for an explanation of these, and other, NCC defined terms. 

H6P1 includes 3 sub-clauses: 

1. The total heating load of the habitable rooms and conditioned spaces in a building must not exceed the heating load limit in Specification 44. 
2. The total cooling load of the habitable rooms and conditioned spaces in a building must not exceed the cooling load limit in Specification 44. 
3. The total thermal energy load of the habitable rooms and conditioned spaces in a building must not exceed the thermal energy load limit in Specification 44. 

Many factors contribute to heating and cooling loads including insulation levels, solar gain, airtightness and local climate.

H6P2 Energy usage

This Performance Requirement sets the minimum performance level for the energy used by a Class 1 building’s domestic services. It includes key fixed appliances such as those for heating, cooling, and lighting, amongst others. 

While this guide is not focused on H6P2, it’s important to remember that it’s mandatory to meet all Performance Requirements in the NCC. So keep this in mind when developing any Performance Solution.

Compliance with the NCC is achieved by complying with the Governing Requirements and relevant Performance Requirements – in this case H6P1. There are 3 options available to demonstrate compliance with the Performance Requirements: 

• a Performance Solution 
• a Deemed-to-Satisfy (DTS) Solution, or 
•  a combination of a Performance Solution and a DTS Solution.

Figure 1 shows the specific compliance options available to meet H6P1. More detailed information can be found in the Housing energy efficiency handbook available from the ABCB website.

DTS Solution

A DTS Solution is a method of satisfying the DTS Provisions. A DTS Solution is achieved by following all appropriate DTS Provisions in the NCC. 

There are 2 DTS pathways for complying with the energy efficiency Performance Requirements: 

• Option 1 (NatHERS): outlined in Chapter 3 of the handbook. 
• Option 2 (Elemental): outlined in Chapter 4 of the handbook.

Performance Solution

A Performance Solution is a method of complying with the Performance Requirements that is not DTS. Unlike the prescriptive DTS Provisions, a Performance Solution is a unique solution providing flexibility in compliance. A Performance Solution can be used for a whole building, a specific element, or a small component.

You can use NCC Verification Methods, or other Assessment Methods to demonstrate that a Performance Solution meets the mandatory Performance Requirements.

Verification Method

A Verification Method is a test, inspection, calculation or other method that determines whether a Performance Solution complies with the relevant Performance Requirement – in this case H6P1. 

There are 2 Verification Methods available for demonstrating compliance with the energy efficiency Performance Requirements: 

• H6V2 Verification using a reference building: outlined in Chapter 5 of the handbook. 
• H6V3 Verification of building envelope sealing: outlined in Chapter 6 of the handbook.

First principles

You can also develop a Performance Solution which demonstrates compliance through direct assessment against the Performance Requirements. In this case, you can use the calculations in Specification 44 to develop a Performance Solution that directly references the specified limits. 

Before we look more closely at Specification 44, let’s review the Performance Solution process.

There are 4 steps to developing a Performance Solution. These are outlined in Clause A2G2(4) and illustrated in Figure 2. Each step needs to be completed before moving on to the next.

The performance-based design brief (PBDB) is the key platform for any proposed design and should be developed in collaboration with the project stakeholders. It must include the acceptance criteria for the proposed Performance Solution, which often requires accounting for the location and characteristics of the building. This is where Specification 44 comes in.

Because H6P1 is quantified, it contains measurable benchmarks that should be used in the acceptance criteria for a PBDB for thermal performance. 

Specification 44 contains the benchmarked load limits for H6P1. These limits vary based on climate factors and floor area. By defining the load limits based on climate factors, load limits can be determined for any home in any climate. 

The quantified heating load limits and cooling load limits in H6P1 were developed with reference to the heating and cooling load limits that were introduced in NCC 2019 as part of the DTS Provisions that form the NatHERS compliance option. The limits have now been generalised for broader use in this Performance Requirement. 

H6P1 allows for higher heating loads in cold locations, and higher cooling loads in hot, humid locations. The limits include an area adjustment to avoid unfairly disadvantaging small houses, which are naturally more exposed to outside conditions than large houses because of their higher ratio of surface area to internal space. 

Remember, to comply with the NCC, a solution must achieve compliance with the Governing Requirements and the Performance Requirements. Clause A2G2 sets out the rules and the process for developing a Performance Solution. It is a matter for an appropriate authority to determine if a particular design is compliant.

You’ll find more guidance on Performance Solutions from the resource library on the ABCB website.

Using the calculation method in Specification 44 is not required in most cases, except where a Performance Solution that references the limits is developed using a first principles approach (i.e. direct assessment against the Performance Requirements). Other compliance options are referenced above and outlined in detail in the Housing energy efficiency handbook.

Using the calculations

If you choose to develop a Performance Solution using the Specification 44 benchmarks, you will need to determine what values to use in the calculations. You could refer to other parts of the NCC, such as Specification 45, or another climate data source. 

The flexibility of using a Performance Solution means that you are not limited in which data you use – as long as that data is used consistently in all relevant calculations associated with your Performance Solution. 

Here are some things to consider:

• Because heating degree hours, cooling degree hours and other terms used in Specification 44 are defined terms in the NCC, any figures you use will need to be in accordance with the definitions in Schedule 1 (all volumes of the NCC). 
• Specification 45 (referenced in J1V5) includes information about heating and cooling degree hours, and dehumidification gram hours for various locations across 8 climate zones. As the Verification Method J1V5 (NCC Volume One) does not directly relate to the Performance Requirement H6P1, it could be considered as part of developing the Performance Solution – but it doesn’t have to be. 
• Remember that it is a matter for the appropriate authority to determine whether a Performance Solution that uses this data is compliant. 

The calculations for Specification 44 are outlined below. Each of these is expressed in Megajoules per square meter per annum (MJ/m².annum).

Remember to check Schedule 1 for a list of NCC defined terms.

S44C2 Heating load limit (HLL)

The heating load limit is determined by taking the greater of two values: the first is a fixed value of 
4 MJ/m².annum, and the second is calculated using the formula:

                                                                             ((0.0044 x HDH) - 5.9)xF_H

This formula incorporates 2 variables: the total annual heating degree hours (HDH) specific to the building's location, and an area adjustment factor (F_H) for the heating load limit, which can be obtained from Table S44C2 based on the total area of the habitable room.

S44C3 Cooling load limit (CLL)

The formula for calculating cooling load limit incorporates several variables. These include the total annual cooling degree hours (CDH) and the total annual dehumidification gram hours (DGH), both specific to the building's location. Additionally, the area adjustment factor (F_C) for the cooling load limit is determined using Table S44C3.

                                                               CLL=(5.4+0.00617×(CDH+1.85DGH))×F_C

S44C4 Thermal energy load limit (TLL)

This is calculated using a formula that considers both the heating and cooling load limits previously calculated, as well as the annual average daily outdoor temperature range (T_r). Each of these elements forms part of the formula stated in this provision for determining the thermal energy load limit for a space.

TLL=19.3HLL+22.6CLL−8.4−15

T_r+10.74

The Performance Requirements of the National Construction Code (NCC) can be met by either using a Performance Solution, a Deemed-to-Satisfy (DTS) Solution, or a combination of both. 

The following is a general representation of the selection and installation of gutters and downpipes, including overflow measures from the ABCB Housing Provisions. The Housing Provisions cover Class 1 and 10 buildings and may be used to meet the DTS Provisions. 

This information is useful for building designers, hydraulic consultants, plumbers, builders and other on-site trades. It is based on the national provisions of the NCC and does not address any state and territory variations. These variations and additions are located in the NCC. The NCC is available at ncc.abcb.gov.au. A gutter, downpipe and overflow (GDO) calculator is also available from the ABCB resource library.

The requirement to install drainage systems from roofs and sub-soil drains should be confirmed with the appropriate authority. These provisions may be applied when roof drainage is connected to a stormwater system. The provisions may no longer be used for box gutters.

An eave gutter is a gutter fixed to a fascia (or an eave) to catch rainwater running off a roof and forms part of a roof drainage system. An eave gutter must be supported by suitably fixed brackets at the stop ends and spaced at not more than 1.2 m along the entire length of the gutter. Eave gutters must have a minimum fall of 1:500 (unless fixed to a metal fascia).

The minimum size required for an eave gutter is dependent on a number of factors. First, you need to consider the location of the building. Different locations have different rainfall intensities that the roof drainage system must be designed to cope with. For selection of eave gutters, a rainfall intensity of 5 minute duration and annual exceedance probability of 5% is used, which is expressed as millimetres per hour (mm/h). Rainfall intensities for different locations are shown in Table 7.4.3d of the Housing Provisions.

When rainfall intensity is identified, the catchment area of the roof (that is to flow into the gutter) must be determined. Typically this is done by multiplying the length of the eave gutter by the distance between the ridge and the eave gutter. For example, if the gutter is 3 metres long and the distance from the gutter to the ridge is 3 metres, then the catchment area of the roof is 9 square metres (3 m x 3 m = 9 m²).

Once the rainfall intensity and roof catchment area are known, the appropriate type/size of eave gutter is selected using Table 7.4.3a in the Housing Provisions.

The Housing Provisions cover 2 eave gutter types:

• rectangular gutters
• D (quad) gutters.

These gutters are then broken down into 6 gutter types (based on their size and shape), labelled A through to F.

Gutter types (as per Table 7.4.3b of the Housing Provisions)

• Gutter type A is a medium rectangular gutter with a minimum cross sectional area of 6,500 mm².
• Gutter type B is a large rectangular gutter with a minimum cross sectional area of 7,900 mm².
• Gutter type C is a 115 mm D gutter with a minimum cross sectional area of 5,200 mm².
• Gutter type D is a 125 mm D gutter with a minimum cross sectional area of 6,300 mm².
• Gutter type E is a 150 mm D gutter with a minimum cross sectional area of 9,000 mm².
• Gutter type F must be designed in accordance with the joint Australian and New Zealand Standard AS/NZS 3500.3.

The Housing Provisions no longer provide requirements for box gutters. Instead, a box gutter must be designed and installed in accordance with AS/NZS 3500.3 or a Performance Solution be developed. Examples of box gutters are shown in Figure 2.

A valley gutter is an exposed open gutter located in the valley of a roof. Valley gutters on a roof must be provided with a pitch more than 12.5 degrees, a minimum freeboard of not less than 15 mm and a side angle of not less than 12.5 degrees. They are also required to have dimensions as set out in Table 7.4.4c of the Housing Provisions for the relevant rainfall intensity. Examples of valley gutters are shown in Figure 3.

A downpipe is a pipe carrying rainwater from a gutter to a sub-surface drainage system or ground level. They are part of a roof drainage system. One downpipe must serve no more than a 12 m length of gutter and must be located as close as possible to valley gutters. The Housing Provisions cover 4 downpipe types as per Table 7.4.3c. They are:

• 75 mm diameter (round)
• 90 mm diameter (round)
• 100 mm x 50 mm (rectangular)
• 100 mm x 75 mm (rectangular).

All of these types of downpipes can be used with all eave gutter types, except for 75 mm diameter (round) downpipes which are not suitable for use with Type E 150 mm D gutters.

The materials used in gutters, downpipes, and flashings need to ensure:

• that no lead is used if forming part of a drinking water catchment area; and 
• that materials are compatible with upstream roofing materials.

Allowing for rainwater overflow is critical in gutter design to minimise the risk of damage to buildings or loss of amenity for occupants. The NCC requires overflow measures capable of coping with a 5 minute duration rainfall intensity and an annual exceedance probability of 1%. The capacity of the selected overflow measures must exceed the overflow volume. These overflow measures can be continuous or dedicated measures. 

An overview of each of these measures is as follows:

• Continuous overflow measures run along a length of gutter, for example, slots at regular intervals along the front face of a gutter. These are discussed further below.
• Dedicated overflow measures are specific points where rainwater overflow can occur, for example, a rainhead. 

These measures can be used separately, or in combination to achieve the required overflow volumes. These are discussed further below.

Continuous overflow measures -The overflow volume for continuous measure (L/s/m) is obtained from Table 7.4.4a which cross references the design 5 minute duration rainfall intensity with the distance from the ridge to the gutter. 

Once the required overflow volume is known, the appropriate overflow measure is selected. Part 7.4 provides 3 examples, see Figure 4.

• Front face slotted gutter (A) provides 0.5 L/s/m of overflow if it has a minimum slot opening area of 1200 mm² per metre of gutter with the lower edge of the slots installed 25 mm below the top of the fascia.
• Controlled back gap (B) provides 1.5 L/s/m of overflow if it has a 10 mm (or greater) spacer permanently installed between the back of the gutter and the fascia. The spacer must be installed at every bracket (and be no more than 50 mm wide). The back of the gutter must be installed a minimum of 10 mm below the top of the fascia.
• Controlled front bead height (C) provides 1.5 L/s/m of overflow if it has the front of the gutter installed a minimum of 10 mm below the top of the fascia.

Dedicated overflow measures The overflow volume for dedicated measure (L/s/m) is obtained from Table 7.4.4b which cross references the design 5 minute duration rainfall intensity with the roof catchment area. 

Once the required overflow volume capacity is known, the appropriate overflow measure is selected. Part 7.4 of the Housing Provisions provides 4 examples, see Figure 5.

• An end stop weir (D) provides 0.5 L/s of overflow if it has a minimum clear width of 100 mm and is installed a minimum of 25 mm below the top of the fascia.
• An inverted nozzle (E) provides 1.2 L/s of overflow if it is installed within 500 mm of the gutter high point with a minimum nozzle size of 100 mm x 50 mm (positioned lengthways in the gutter). The top of the nozzle must be a minimum of 25 mm below the top of the fascia.
• A front face weir (F) provides 1.0 L/s of overflow if it has a minimum clear width of 200 mm with a minimum height of 20 mm. The weir edge must be installed 25 mm below the top of the fascia.
• A rainhead (G) provides 3.5 L/s of overflow if it has a 75mm diameter hole in its outer face with the centre line of the hole positioned 100 mm below the top of the fascia. Figure 5 Examples of dedicated overflow measures.

The National Construction Code (NCC) is Australia’s performance-based building and plumbing code. It sets the minimum technical requirements for the construction of new buildings (and new building work in existing buildings). 

This document gives an overview of the Assessment Methods contained in the NCC. Assessment Methods are used when determining if a Performance Solution or Deemed-to-Satisfy (DTS) Solution complies with the relevant Performance Requirements.

Compliance with the NCC’s mandatory Performance Requirements is achieved by developing a Performance Solution, a DTS Solution, or a combination of the two. A Performance Solution uses any method other than the DTS Provisions to comply with the Performance Requirements. DTS Solutions use the NCC’s DTS Provisions to comply with the Performance Requirements.

The following Assessment Methods are listed in the NCC and each, or any combination, can be used:

• Evidence of suitability
• Comparison with the DTS Provisions
• Verification Methods
• Expert Judgement. 

Evidence of suitability, also known as ‘documentary evidence’, can generally be used to support that a material, product, form of construction or design satisfies a Performance Requirement or a DTS Provision. The form of evidence that may be used consists of one, or a combination, of the following:

• A report from an Accredited Testing Laboratory. 
• A Certificate of Conformity or a Certificate of Accreditation. 
• A certificate from a professional engineer or appropriately qualified person. 
• A current certificate issued by a product certification body that has been accredited by the Joint Accreditation System of Australia and New Zealand (JASANZ)
• Any other form of documentary evidence that adequately demonstrates suitability such as a Product Technical Statement.

This Assessment Method involves a comparative analysis demonstrating that a Performance Solution is better than, or at least equivalent to, the relevant DTS Provision(s). To carry out this comparison, the applicable DTS Provision(s) and Performance Solution both need to be subject to the same level of analysis using the same methodology. This provides the building designer and appropriate authority with a defined benchmark or level for the DTS Provision and the Performance Solution.

Following this method determines whether the Performance Solution provides the same level of health, safety, amenity or sustainability as using the DTS Provisions. In some cases, technical analysis would be carried out using calculation methods such as computer modelling to prove compliance. If it is found that the Performance Solution is equal to or better than the relevant DTS Provision(s), then the Performance Solution proposal satisfies the NCC Performance Requirements.

Verification Methods are tests or calculations prescribing a way to comply with the NCC Performance Requirements. They take a number of forms including a test, inspection, calculation, or a combination of these.

A Verification Method provides a methodology for assessing a Performance Solution. It generally includes a quantifiable benchmark or predetermined acceptable criteria that the solution must achieve. 

The NCC contains several Verification Methods addressing some of the Performance Requirements. Verification Methods not in the NCC may be used, if they are deemed suitable by the appropriate authority.

A test

A test verifies a product or system achieves a certain performance level. An example is an on-site field test to determine the actual thermal performance of a window installed in a building.

An inspection

An inspection is typically a visual examination to ensure a component is constructed or installed in a manner that satisfies the Performance Requirement. The inspection may need to be undertaken by an appropriately qualified person.

A calculation 

Engineering calculations, including computer modelling or hand calculations, may be used to verify a design will achieve the expectation of the relevant Performance Requirements.

Other methods

This allows any other suitable method to prove a design, construction or individual component meets a Performance Requirement. There are many options available for use as a Verification Method. However, there must be agreement with the appropriate authority that the Verification Method is acceptable. 

Other Verification Methods

Other Verification Methods, by definition, allow almost any methodology or procedure to be used to verify a Performance Solution, subject to that method being suitable and used in the appropriate way.

Where physical criteria is unable to be tested or modelled by calculation, the opinion of an expert may be accepted. This is referred to as the use of Expert Judgement. In other words, the judgement of a person who has the qualifications and experience necessary to determine whether a Performance Solution or DTS Solution complies with the Performance Requirements. In some instances, Expert Judgement can be used in combination with other Assessment Methods.

Who is an expert? 

An expert is someone who can make a judgement relating to NCC compliance. This means they need to be skilled and experienced in the area on which they are providing judgement. They could be a suitably qualified engineer or topic matter expert.

Different types of experts may need to be registered with state and territory accreditation bodies or registrars. Note that what is legally defined as an expert will differ for individual states and territories.

Ultimately, it is the role of the appropriate authority to determine whether a particular person providing an Expert Judgement is considered an expert. Each situation is different, so the capacity of the expert to provide credible evidence in regards to the issue being considered must be individually assessed.

Note that typically under state and territory laws, the appropriate authority independently assesses the proposal and therefore cannot provide an Expert Judgement for a matter they are considering for approval.

The key to the use of Assessment Methods is appropriate documentation. Documentation should show that the solution complies with the relevant DTS Provisions and/or Performance Requirements, and reflect the Assessment Method(s) used. Documentation should be collated in such a way that it clearly demonstrates to the appropriate authority:

• the applicable Performance Requirement(s) and/or DTS Provision(s)
• the Assessment Methods used
• for Performance Solutions, details of the performance-based design brief (PBDB), analysis and evaluation undertaken
• confirmation that the applicable Performance Requirement(s) and/or DTS Provision(s) have been met
• for Performance Solutions, details of conditions or limitations, if any exist.

Remember it is the responsibility of the appropriate authority to determine how much and what level of detail is required when accepting Assessment Methods.

The National Construction Code (NCC) is Australia’s performance-based building and plumbing code. It sets the minimum technical requirements for the construction of new buildings (and new building work in existing buildings). 

This document gives an overview of options available to demonstrate compliance with the NCC. This information is useful for all NCC users.

The NCC is a performance-based code. This means that a building, plumbing or drainage solution will comply with the NCC if it satisfies the relevant Performance Requirements. Compliance with the NCC is achieved by complying with the:

1. Governing Requirements.
2. relevant Performance Requirements.

The Governing Requirements are a set of governing rules outlining how the NCC must be used and the process that must be followed.

The Performance Requirements prescribe the minimum necessary requirements for buildings, building elements, and plumbing and drainage systems. They must be met to demonstrate compliance with the NCC.

There are three ways to comply with the NCC’s Performance Requirements. These include using a: 

• Performance Solution
• Deemed-to-Satisfy (DTS) Solution
• combination of Performance Solutions and DTS Solutions.

A Performance Solution must comply with all applicable Performance Requirements of the NCC. A Performance Solution provides a tailored solution to meet the intended objective of the Performance Requirements.

A Performance Solution must comply with all relevant Performance Requirements and must be verified using one or a combination of the following Assessment Methods:

• Evidence of Suitability.
• A Verification Method.
• Expert Judgement. 
• Comparison with the DTS Provisions.

The NCC also prescribes the following process that practitioners must undertake when developing a Performance Solution: 

1. Develop a performance-based design brief with appropriate stakeholders.
2. Carry out analysis.
3. Evaluate results.
4. Prepare a final report outlining steps 1 to 3. 

A DTS Solution is achieved by following all appropriate DTS Provisions in the NCC. The DTS Provisions are prescriptive (i.e. like a recipe book, they tell you how, what and in which location things must be done). They include materials, components, design factors, and construction methods that, if used, are deemed to meet the Performance Requirements. Hence the term `Deemed-to-Satisfy’.

A DTS Solution must comply with the relevant Performance Requirements. It must be verified using one or a combination of the following Assessment Methods:

• Evidence of suitability.
• Expert Judgement. 

When designing a building, both Performance Solutions and DTS Solutions can be used to achieve compliance with Performance Requirements.

A combination of solutions may be used to satisfy a single Performance Requirement. This may include occasions where a specific Performance Requirement covers a number of elements within a building. 

When using a combination of solutions, the relevant Performance Requirements must be identified by reviewing the:

• DTS Provisions of each Section/Part for the solution; and Performance Requirements from these Sections/Parts; and
• Performance Requirements from other Sections/Parts relevant to or affected by the proposed solution.

When using a combination of compliance solutions, the appropriate Assessment Methods must be used. That means where a Performance Requirement is met by a Performance Solution; then evidence of suitability, a Verification Method, Expert Judgement and/or Comparison with the DTS Provisions must be used. The Performance Solution process must also be followed for this portion of the design.

If a DTS Solution is used to meet the Performance Requirements; then evidence of suitability and/or Expert Judgement must be used.

More information about NCC Assessment Methods is provided in the ABCB publication, NCC Navigator - Assessment Methods NCC 2022.

The National Construction Code (NCC) sets out the minimum technical requirements for new buildings (and new building work in existing buildings) in Australia. In doing so, it groups buildings by their use. These groups are assigned a classification which is then how buildings are referred to throughout the NCC. This information is crucial for all NCC users.

The following is a general representation of the building classifications in the NCC. It is based on a national perspective and does not address any state or territory variations. 

State and territory variations and additions to the NCC are located in the NCC (Schedules 4-11).

Building classifications are referenced in Section A of the Governing Requirements, Part A6 of the NCC.

Building classifications are labelled ‘Class 1’ through to ‘Class 10’. Some classifications also have sub-classifications, referred to by a letter after the number (e.g. Class 1a).

Class 2 to 9 buildings are mostly covered by Volume One, and Class 1 and 10 buildings are mostly covered by Volume Two. Volume Three of the NCC refers to all building classifications.

A building may have parts with different uses. In most cases, each of these parts are classified separately.

A building (or part of a building) may also have more than one use and may be assigned more than one classification.

Class 1 buildings are houses. Typically, they are standalone single dwellings of a domestic or residential nature.

These buildings can also be horizontally attached to other Class 1 buildings. 

When attached they are commonly referred to as duplexes, terrace houses, row houses and town houses. In these situations, they must be separated by a wall with fire-resisting and sound insulation properties.

The Class 1 classification includes 2 sub-classifications: Class 1a and Class 1b.

A Class 1a building is a single dwelling being a detached house; or one of a group of attached dwellings being a town house, row house or the like. 

A Class 1b building is a boarding house, guest house or hostel that has a floor area less than 300 m² and ordinarily has less than 12 people living in it. It can also be 4 or more single dwellings located on one allotment which are used for short-term holiday accommodation.

Class 2 buildings are apartment buildings. They are typically multi-unit residential buildings where people live above and below each other. The NCC describes the space considered as an apartment as a sole-occupancy unit (SOU). 

Class 2 buildings may also be single storey attached dwellings with a common space below. For example, 2 dwellings above a common basement or carpark.

Class 3 applies to residential buildings other than Class 1 or Class 2 buildings, or a Class 4 part of a building. Class 3 buildings are a common place of long term or transient living for a number of unrelated people.

Examples include a boarding house, guest house, hostel or backpackers (that are larger than the limits for a Class 1b building). Class 3 buildings could also include dormitory style accommodation, or workers’ quarters for shearers or fruit pickers.

Class 3 buildings may also be ‘care-type’ facilities such as accommodation buildings for children, the elderly, or people with disability, which are not Class 9 buildings.

A Class 4 part of a building is a sole dwelling or residence within a building of a non-residential nature. An example of a Class 4 part of a building would be a caretaker’s residence in a storage facility. A Class 4 part can only be located in a Class 5 to 9 building.

Class 5 buildings are office buildings used for professional or commercial purposes.

Examples of Class 5 buildings are offices for lawyers, accountants, government agencies and architects.

Class 6 buildings are typically shops, restaurants and cafés. They are a place for the sale of retail goods or the supply of services direct to the public.

Some examples are:

• A dining room, bar, shop or kiosk part of a hotel or motel.
• A hairdresser or barber shop. 
• A public laundry.
• A market or showroom.
• A funeral parlour.
• A shopping centre.

Class 7 buildings are storage-type buildings. The Class 7 classification has 2 sub-classifications: Class 7a and Class 7b.

Class 7a buildings are carparks. 

Class 7b buildings are typically warehouses, storage buildings or buildings for the display of goods (or produce) for wholesale.

A factory is the most common way to describe a Class 8 building. It’s a building in which a process (or handicraft) is carried out for trade, sale, or gain. 

The building can be used for production, assembling, altering, repairing, finishing, packing, or cleaning of goods or produce. It includes buildings such as a mechanic’s workshop. It may also be a building for food processing, such as an abattoir.

Class 9 buildings are buildings of a public nature. The Class 9 classification has three sub-classifications: Class 9a, Class 9b and Class 9c.

Class 9a buildings are generally hospitals, referred to as health-care buildings in the NCC. They are buildings in which occupants or patients undergo medical treatment and may need physical assistance to evacuate in the case of an emergency. This includes a clinic (or day surgery) where the effects of the treatment administered involve patients becoming unconscious or unable to move. This in turn requires supervised medical care (on the premises) for some time after treatment has been administered.

Class 9b buildings are assembly buildings in which people may gather for social, theatrical, political, religious or civil purposes. They include schools, universities, childcare centres, pre-schools, sporting facilities, night clubs, or public transport buildings.

Class 9c buildings are residential care buildings that may contain residents who have various care level needs. They are a place of residence where 10% or more of persons who reside there need physical assistance in conducting their daily activities and to evacuate the building during an emergency. An aged care building, where residents are provided with personal care services, is a Class 9c building.

Class 10 buildings are non-habitable buildings or structures. Class 10 includes three sub-classifications: Class 10a, Class 10b and Class 10c.

Class 10a buildings are non-habitable buildings including sheds, carports, and private garages. 

Class 10b is a structure being a fence, mast, antenna, retaining wall, swimming pool, or the like.

A Class 10c building is a private bushfire shelter. A private bushfire shelter is a structure associated with, but not attached to, a Class 1a building.

As buildings can have mixed uses, they can also have mixed (or multiple) classifications. For example, a building may have a basement carpark (Class 7a) with ground floor retail space (Class 6) and residential apartments (Class 2) and offices above (Class 5).

A building (or a part of a building) may be designed to serve multiple purposes and may have more than one classification. This means that it is permissible for a building to be Class 6/7, or Class 5/6, or whatever is deemed appropriate.

This allows flexibility in how the building might be used. For example, if a building is intended for retail shopping, storage or office space, it may be designed as a Class 5/6/7 building.

At the design stage it may not be clear who the final tenant will be (or how they will be using their tenancy), so as long as the design meets the minimum requirements of all the classifications it could be used for any of the purposes.