ENERGY-EFFICIENT BUILDING ENVELOPES NCC 2019’s Revised Section J and its Impact on Facade System Design

The building sector accounts for approximately 19% of total energy consumption and 23% of greenhouse gas emissions in Australia.1 Efforts to improve energy efficiency of the Australian built environment slowed post 2010, but changes to National Construction Code (NCC) Volume 1 in 2019 and expected changes to Volume 2 in 2022 are set to reinvigorate the industry’s focus on the design and construction of building envelopes to optimise thermal performance.

A key objective of the changes in NCC 2019, especially the new Section J, is to deliver higher performing buildings in terms of energy efficiency and reduced greenhouse gas (GHG) emissions. One of the major changes to the NCC 2019 is the increased requirement for thermal performance, which has mostly been achieved through rebalancing the contribution of the building envelope to energy efficiency.

In particular, glazing is required to contribute more to the task in commercial buildings. It was felt that requirements for thermal performance was carried disproportionately by wall components, while a high portion of the energy is lost through large areas of low-performing glazing. The new Section J treats glazing and wall components as co-contributors to the building envelope and therefore their performance will be calculated together.

In this whitepaper, we take a closer look at the changes relating to the new energy efficiency requirements in Section J and explore how these can be met using efficient building envelopes that reduce building energy consumption rates.

INTRODUCTION

The most significant change in NCC 2019, the rewriting of Section J, sets out new energy efficient requirements for commercial buildings, which align with the COAG’s National Energy Productivity Plan to reduce emissions and improve energy efficiency by 40% by 2030.

In the Council of Australian Governments (COAG) 2012 Report “Baseline Energy Consumption and Greenhouse Gas Emissions in Commercial Buildings Australia”,2 it was found that total energy consumption3 in commercial buildings (covered by this study) represented around 3.5% of gross final energy consumption in Australia in 2009. However, GHGs associated with this energy use represented 6% of Australia’s total net emissions (excluding land use, land use change and forestry) in that year,4 a much higher proportion as the fuel mix is weighted towards electricity and, on average across Australia, electricity has higher GHG intensity than other energy sources. Heating, ventilation and air conditioning (HVAC) are generally the largest end use of electricity.5 This underpins the drive to refocus regulations away from just energy efficiency and to look more at GHG emissions holistically.

The most significant change in NCC 2019, the rewriting of Section J, sets out new energy efficient requirements for commercial buildings, which align with the COAG’s National Energy Productivity Plan to reduce emissions and improve energy efficiency by 40% by 2030.6 To support this, measurement of the performance of elements such as lighting and HVAC were shifted from an energy-based metric to a GHG emissions-based metric in a bid to allow

more accurate assessment of building performance, particularly in extreme temperatures.

With this new focus, the revised Section J in NCC 2019 includes:

• new provisions for walls and wall systems;

• new Verification Methods for NABERS (National Australian Built Environment Rating System) and Green Star tools, paramount for rating the sustainability of buildings; and

• the glazing component of Part J2 has been removed and glazing is now incorporated into the performance requirements for the overall building fabric in Part J1.

The balance between wall components and glazing has been addressed with target specifications for the total facade in the new Part J1. New specifications are included to aid with the calculation of U-Value and solar admittance of wall and glazing construction. The same building facade may require improved glazing or a reduction in the glazing-to-wall ratio compared to 2016. A facade calculator tool to calculate the thermal performance has been prepared by the Australian Building Codes Board (ABCB) to assist designers.7

WHY FOCUS ON ENERGY EFFICIENCY AND GREENHOUSE GASES?

Insulation

Under NCC 2019, insulation requirements have also changed. In general, these changes are as follows:

• insulation must not affect the safety or effective operation of a service or fitting;

• reflective insulation must be installed with an air gap to be effective;

• bulk insulation must be installed so that it maintains its position and thickness;

• calculation of R-Value must include an allowance for thermal bridging; and

• amendments to AS/NZS 4859.1:2002 and AS/NZS 4859.2:2018, the Australian standards relating to the materials used for the thermal insulation of buildings.

The changes to AS/NZS 4859.1:2002 and AS/NZS 4859.2:2018 include:

• a wider range of insulation materials;

• a new standard for labelling;

• reporting of aged R-Value for Polyisocyanurate Foam (PIR), Polyurethane Foam (PUR) and Extruded Polystyrene (XPS) materials.

• Expanded Polystyrene Fire Resistant (EPS-FR) and Mineral Wool (MW) do not require aging; and

• declaring R-Values at 23°C in Australia and 15°C in New Zealand.

Building fabric and glazing

Previously treated separately, walls and glazing are now part of one facade system with an average U-Value. Also, whereas U-Value and Solar Heat Gain Coefficient (SHGC) were dependent on one another, now they must be calculated separately and the Deemed-to-Satisfy (DTS) glazing specification must be selected from the Window Energy Rating Scheme (WERS) or similar calculator.

Total R-Value includes the R-Value of all the layers of building elements that make up the wall system, which may include the outdoor airfilm, masonry, cavity airspace, plasterboard and the indoor airfilm. When evaluating facade performance, R-Value must be determined allowing for the effects of thermal bridging (see below discussion on thermal bridging). This applies to walls and windows of the building envelope. In some instances, this can include an internal wall, such as a wall adjacent to an internal courtyard, that is exposed to external environments even if it is within the roof line.

Assessing wall-glazing construction

If the glazing is greater than 20% of the wall/glazing combination, then the required R-Value of the wall component is 1.0, because in this case the glazing is considered to be the primary driver of energy efficiency. If the glazing is less than 20%, then Table J1.5a from NCC 2019 is referenced for minimum wall Total R-Value based on climate zones and building class.

NCC 2019 specifies two methods for calculating Total system U-Value:

• Method 1. Each of the four orientations (North, South, East, West) are examined independently,

• Method 2. All four orientations are looked at together and a weighted average is used. In this case, a poor-performing facade on one side of the building can be offset by a better performing facade on another side.

Note that the ABCB advises that for complicated wall-glazing combinations the ABCB facade calculator is a good option.

NCC 2019 CHANGES IN PRACTICE

Example: Total system U-Value calculation using Method 1

Consider a wall facing North in a Class 6 building in Climate Zone 7 consisting of 2.5m2 of glazing and 17.5m2 of wall area. The wall is a stud wall with 3mm aluminium sheeting, bulk insulation with R-Value 1.5 and 13mm thick plasterboard, giving a Total R-Value of 1.54 (calculated as per AS/NZS 4859.2:2018 allowing for thermal bridging).

The wall area is 1.5/20 or 87.5% of the wall-glazing construction. As the wall area is greater than 80% of the wall-glazing construction, the minimum R-Value required per Table J1.5a is 1.4. As R-Value 1.54 is greater than the minimum required 1.4, the wall component meets the requirement.

Total system U-Value of the wall component is calculated as the inverse of Total R-Value, that is 1/1.54 = 0.65. Total system U-Value is calculated as the area weighted value of each component. As walling is 87.5% and glazing is 12.5%, the calculation is: 0.875 x 0.65 + 0.125 x 3.5 = U1.0. This is less than the requirement in J1.5(a)(i) of the NCC, which is U2.0, so the wall-glazing system meets J1.5 and Specification J1.5(a) requirements. This example is drawn from the ABCB’s Handbook: Energy Efficiency NCC Volume One.

Solar admittance calculation

In NCC 2019, solar admittance is calculated in accordance with Specification J1.5a. The maximum values are specified in Tables J1.5b and J1.5c (in the NCC). Again, two methods are given: Method 1 considers a single aspect and Method 2 considers multiple aspects. Method 2 requires a representative air conditioning energy value less than that achieved by the reference solar admittance. The calculation takes into account the area of each wall-glazing construction, the solar admittance weighting coefficient of each aspect, and the wall-glazing construction solar admittance.

For glazing on an aspect with an area of less than 20% of wall-glazing construction, the solar admittance is zero. Where glazing is less than 20%, ABCB recommends using Method 1. Where there are large numbers of different wall-glazing construction elements, ABCB recommends using the ABCB facade calculator as a quicker way to do calculations. Retail display areas have less stringent requirements, but the concessions are strictly applicable to display areas, such as automobile showrooms and shop fronts, but not restaurants or cafes.

Roofing

Over the past 20 years, there has been a trend away from dark roof colours – this has been continued under NCC 2019. Dark-coloured roofs will no longer be permitted under DTS provisions. Commercial buildings will need a light-coloured roof, with all Climate Zones (except Climate Zone 8) requiring a maximum solar absorptance of 0.45 to comply. This means that any roof assessed under

the relevant DTS provisions will need to be Whitehaven, Surfmist, Classic Cream, Paperbark, Shale Grey or Evening Haze. Medium or dark-coloured roofs, including green roofs, dark concrete and membrane roofs require a performance-based solution using Verification Method JV3 to demonstrate compliance.

Thermal bridging and thermal breaks

When highly conductive materials touch, they create a bridge for heat transfer (gain or loss). Insulation must now include the implications of thermal bridging as detailed in AS/NZS 4859.2:2018, which can significantly change the wall Total R-Value. Consequently, facades with metal framing will require thermal breaks to prevent a bridge. To accommodate this, the target R-Values for buildings have been reduced, but thermal bridging must be included in the calculation.

One example of the impact of these requirements can be seen on a conventional fibre cement clad, metal stud wall. When calculated under AS/NZS 4859.2:2018 allowing for thermal bridging, the R-Value is 0.86 (here thermal bridging reduces the R-Value of the stud wall and bulk insulation from R 2.25 to R 0.61). However, once the wall has the addition of a thermal break, the system R-Value rises to 1.49, which is above the new minimum requirement in this case of 1.0.

In the example above, if a continuous insulation system (i.e. 140mm insulated panels) were used, then the R-Value with thermal bridging is 3.86 and when thermally broken is 3.23, a decrease of only 16%.

andforestry)inthatyear,4amuchhigherproportionbecauseasthefuelmixisweightedtowardselectricityand,onaverageacrossAustralia,electricityhashighergreenhousegasintensitythanotherenergysources.Emissionsincommercialbuildingsareexpectedtogrowatasimilarratetototalenergyconsumption,thatis,by27%overtheperiod2009to2020.

Endenergyuseconsistentwithotherstudies,heating,ventilationandairconditioning(HVAC)isgenerallythelargestenduseofelectricity:

ThisunderpinssomeofthedrivetorefocusregulationsawayfromjustenergyefficiencyandtolookmoreatGHGemissions,andhasledtothemostsignificantchangeinNCC2019,therewritingofSectionJ,settingoutnewenergyefficientrequirementsforcommercialbuildings.ThechangesaimtoalignwiththeCOAGNationalEnergyProductivityPlanandreduceemissionsandimproveenergyefficiencyby40%by2030.

Tosupportthis,measurementoftheperformanceofelementssuchaslightingandHVAChasshiftedfromanenergy-basedmetrictoagreenhousegasemissions-basedmetric5inabidtoallowmoreaccurateassessmentofbuildingperformance,particularlyinextremetemperatures.

ToaccommodatethisnewfocustherevisedSectionJincludes:· Newprovisionsforwallsandwallsystems,· NewVerificationMethodsforNABERSandGreenStartools,paramountforratingthesustainabilityof

buildings,· The balance between wall components and glazing has been addressed with the glazing Part J2

removedandtheglazingincorporatedintotheoverallbuildingfabric,PartJ1.

NewspecificationsareincludedtoaidwiththecalculationofU-Valueandsolaradmittanceofawallandglazingconstruction.Thesamebuildingfaçademayrequireimprovedglazingorareductionintheglazingtowallratiocomparedto2016.AfaçadecalculatortooltocalculatethethermalperformanceofthefaçadehasbeenpreparedbyABCBtoassistdesigners.Insulationingeneral

Somegeneralchangesrelatingtoinsulationare• Insulationmustnotaffectthesafetyoreffectiveoperationofaserviceorfitting,

4 DCCEE (2012), p. 16. 5https://backtobasics.edu.au/2019/02/ncc-2019-updates/

43%

26%

20%

2%10%

Averageallperiods,n=1150

HVAC

Lighting

TotalEquipment

Domestichotwater

• Reflectiveinsulationmustbeinstalledwithanairgaptobeeffective,• Bulkinsulationmustbeinstalledsothatitmaintainsitspositionandthickness,• CalculationofR-valuemustincludeanallowanceforthermalbridging,• AmendmentstoAS/NZS4859parts1&2.Specifically,theinclusionof

• awiderrangeofinsulationmaterials,• anewstandardforlabelling,• reportingofagedR-ValueforPIR,PURandXPSmaterials(EPS-FRandMWdonotrequire

aging),• declaringR-Valuesat23oCinAustraliaand15oCinNewZealand.

BuildingFabricandGlazing

Amajorchangehasbeenthetreatmentofwallsandglazing.Previouslytreatedseparately,theyarenowpartofonefaçadesystemwithanaverageU-value.Also,whereasU-valueandSolarHeatGainCoefficient(SHGC)weredependentononeanother,nowtheymustbecalculatedseparatelyandtheDTSglazingspecificationmustbeselectedfromtheWindowEnergyRatingScheme(WERS)orsimilarcalculator.

Typically,totalR-Value(Rt)includestheR-Valueofallthelayersofbuildingelementsthatmakeupthewallsystem.Forexample,thismayincludetheoutdoorairfilm,masonry,cavityairspace,plasterboardandtheindoorairfilm.Whenevaluatingfaçadeperformance,Rtmustbedeterminedallowingfortheeffectsofthermalbridging(seesectiononthermalbridging).Thisappliestowallsandwindowsofthebuildingenvelope.Insomeinstances,thiscanincludeaninternalwall,suchasawalladjacenttoaninternalcourtyard,thatisexposedtoexternalenvironmentsevenifitiswithintheroofline.

Assessingthewall

Iftheglazingisgreaterthan20%ofthewall/glazingcombination,thentherequiredRtofthewallcomponentis1.0.Becauseinthiscasetheglazingisconsideredtobetheprimarydriverofenergyefficiency.Iftheglazingislessthan20%,thentableJ1.5afromNCC2019isreferencedforminimumwallRtbasedonclimatezonesandbuildingclass.

NCC2019specifiestwomethodsforcalculatingtotalfaçadeU-Value:

• Method1–eachofthefourorientations(North,South,East,West)areexaminedindependently,• Method2–allfourorientationsarelookedattogetherandaweightedaverageisused.Inthiscasea

poorperformingfaçadecanbeoffsetbyabetterperformingfaçade.

Note:ABCBadvisethatforcomplicatedwall-glazingcombinationstheABCBfaçadecalculatorisagoodoption

LEFT End energy use consistent with other studies, heating, ventilation and air conditioning (HVAC) is generally the largest end use of electricity.

BELOW If the glazing is greater than 20% of the wall / glazing combination, then the required Rt of the wall component is 1.0. In this case, the glazing is considered to be the primary driver of energy efficiency. If the glazing is less than 20%, then table J1.5a from NCC 2019 is referenced for minimum wall Rt based on climate zones and building class.

The inherent advantages of Insulated Sandwich Panels (ISP) address many of the issues covered by the changes in the NCC 2019. ISPs are made when three separate elements – an outer steel skin, inner core (typically comprised of EPS-FR, PUR, PIR or MW) – are “sandwiched together” into one structure.8

Due to the following advantages, ISPs are the most suitable product for driving the construction sector to an energy-efficient, low GHG future:

• ISPs provide continuous insulation, which means thermal bridging is minimal compared to conventional construction methods;

• The insulation in ISPs is held in place without degrading, crumbling, sagging, or any gaps, and maintains its performance throughout the life of the building; and

• ISPs provide an airtight seal, meaning there will be no infiltration or exfiltration of warm or cold air through panel joints.

Bondor_Metecno is Australia’s leading manufacturer of insulated sandwich panels. Founded in the 1950s, the group is constantly working on solutions for industrial, commercial and residential building customers across Australia and offers the most comprehensive range of insulated panel products and systems available. Having operated in the industry for 65 years, Bondor takes pride in being an Australian manufacturer.

The company is a passionate supporter of Australian standards for Australian conditions. Its products have been approved and tested to Australian standards, while adhering to the strictest international regulations.

Bondor_Metecno has technical and support associations with several international building product suppliers, universities and research facilities in Australia. The company remains up to date with industry trends and regulations through its involvement with the Insulated Panel Council of Australasia and the FM Approvals International Advisory Council.

For more information, visit the Bondor website at bondor.com.au

INSULATED SANDWICH PANELS – A DESIGN SOLUTION

BONDOR_METECNO

The new Section J treats glazing and wall components as co-contributors to the building envelope and therefore their performance will be calculated together.

All information provided correct as of December 2020

REFERENCES1 Victoria Government. “Energy Efficient Office Buildings: Transforming the Mid-Tier Sector.” Sustainability Victoria. https://www.sustainability.vic.gov.au/-/media/SV/Publica-

tions/Business/Commercial-building-efficiency/Sector-research-and-reports/Energy-Efficient-Office-Buildings-Nov-2016.pdf (accessed 17 November 2020).2 Department of Climate Change and Energy Efficiency. “Baseline Energy Consumption and Greenhouse Gas Emissions in Commercial Buildings Australia.” energy.gov.au.

https://www.energy.gov.au/publications/baseline-energy-consumption-and-greenhouse-gas-emissions-commercial-buildings-australia (accessed 17 November 2020).3 Note that all references to “energy consumption” in this Report relate to the consumption of final energy sources, including electricity.

Conversion losses associated with the transformation of primary fuels into electricity are not included. 4 Above n 2.5 Australian Government. “HVAC Energy Breakdown.” Department of Agriculture, Water and the Environment.

https://www.environment.gov.au/system/files/energy/files/hvac-factsheet-energy-breakdown.pdf (accessed 17 November 2020).6 Australian Government. “National Energy Productivity Plan.” energy.gov.au.

https://www.energy.gov.au/government-priorities/energy-productivity-and-energy-efficiency/national-energy-productivity-plan (accessed 17 November 2020).7 Australian Building Codes Board. “Facade Calculator.” ABCB.

https://www.abcb.gov.au/Resources/Tools-Calculators/facade-calculator-ncc-2019-volume-one (accessed 17 November 2020).8 Insulated Panel Council Australasia Ltd. “What are insulated sandwich panels?” IPCA.

http://www.insulatedpanelcouncil.org/insulated-sandwich-panel (accessed 17 November 2020).