Project Outline: 6-Star - Planning for Better Outcomes

Published: 04 April 2011 / Amendment 1 / BCA 2011

...excerpt only - see link at the bottom of the page to download the full text.

BCA 2011 Part 3.12 ENERGY EFFICIENCY

The WA Variation has been removed and the 6-Star provisions will apply for BCA 2011.

Building Regulations 1989 6(2) provides local government with a transitional period of up to 12-months in which they can approve building work under the previous (BCA 2010) provisions.

To resolve how transition provisions are applied Building Commission publish Advisory Note 2011/013 outlining changes to Building Regulations 1989 that will enforce the use of the transition provisions (go to http://www.buildingcommission.wa.gov.au/bc/Advisory_Notes.aspx).

The evidence gathered while undertaking this project (see Sidebar Notes) suggests that builders and designers have significant design, supply, construction and building process issues to resolve before it is reasonable to expect them to deliver good practice 6-Star Modelling compliance. As such ABLE believes there is a legitimate technical case for the transition period to being allowed.

6-STAR – DTS OR MODELLING?

BCA 3.12.0 Application of Part 3.12 provides two Acceptable Construction Practice (ACP) options for determining compliance:

• 3.12.0 (a) (i) – using House Energy Rating Software (BERS, AccuRate, FirstRate) to verify a minimum 6-Star rating (Modelling – see page 1 Sidebar Note) plus compliance with nominated ACP provisions and Part 3.12.5 Services (see 3.12.0 – Application of Part 3.12), or
• 3.12.0 (a) (ii) – the current practice DTS method; compliance with the ACP provisions for Building Fabric, External Glazing, Building Sealing, Air Movement and Part 3.12.5 Services.

In late 2010 ABLE completed the Local Practice Project: 6-Star – DTS or Modelling?

For the nine project homes assessed the outcome seemed to be – Modelling is the better 6-Star compliance option (see sidebar note).

6-STAR – PLANNING FOR BETTER OUTCOMES

If Modelling is a better option than DTS, and DTS is the current verification method, then builders and designers have a steep learning curve if they are to understand the better practices needed to achieve 6-Star compliance. Project builders will also have to undertake a large volume of Modelling work to verify that current standard plans achieve a 6-Star rating in a range of different Climate Zones and orientations.

The purpose of Local Practice Project was to research and investigate:

• The likely scope of the assessment work that will be required.
• How assessment data could be used to profile the thermal performance of standard designs to inform house-for-site selection and ongoing product development.
• Outcomes differences between the four Metropolitan/Peel area Climate Zones and between different orientations for the same standard design.
• Construction options for improving thermal performance and their cost effectiveness.
• Design options for improving thermal performance and the cost impact of poor decisions.
• Performance differences between BERS and AccuRate Modelling software.The likely process and construction cost impact of 6-Star compliance.

The intent of this project is to provide information that will enable builders and designers to better manage the transition from 5-Star DTS to 6-Star Modelling.

PROJECT SAMPLE

ABLE invited metropolitan and regional builders and designers who undertake Project, One-Off and Alterations & Additions work to participate in this project.

Five builders accepted the invitation. Each builder was asked to provide plans for houses that are either current display houses or current “sellers”. From this range the 25 houses selected to use in the project included:

• Project Homes – 18 x single storey (101–234m2) and 4 x double storey (253–346m2).
• One-Off homes – 3 x double storey (230–268m2).

Figure 1 provides a schedule listing each house, its project number (used to report findings in other Local Practice Notes) and a range common reference data (floor area, price range etc).

SCOPE OF REPORTING

From the work undertaken, likely issues are:

• Construction improvement alone may not be sufficient to achieve a 6-Star rating.
• If verification is left until after the design is documented, failure to achieve 6-Star means the building is non-compliant – unless significant design changes are made.
• Design decisions that can make 6-Star difficult to achieve are: high glazing to floor area percentages that already require improved glazing to achieve 5-Star DTS compliance, the NatHERS area adjustment factor that penalises houses over 200m2 Net Conditioned Floor Area (NCFA) and NatHERS zoning protocols that can penalise void spaces.

Issues discovered while undertaking other research are:

• DTS Glazing Calculator outcomes are likely to fail when fixed existing house orientations do not allow for sufficient area of northern glazing.
• Modelling can only be used if there is a WA “Alterations & Additions Protocol” that allows for “whole of house assessment” and “new work only construction compliance” (similar to that used in South Australia).

Investigation undertaken for the previously completed 6-Star – DTS or Modelling?” project (see Sidebar Note) suggests Modelling using NatHERS Climate Zones (see sidebar) will mean:

• Kalgoorlie and Albany – 6-Star will be harder to achieve than 5-Star DTS.
• Bunbury – outcomes are the same as those reported for Mandurah (see results that follow).
• Busselton/Margaret River – outcomes will be similar to those reported for Albany because Modelling in these areas uses Manjimup and Albany Climate Zones.
• Geraldton – 6-Star is likely to be easily achieved.

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