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Thinking beyond 6 Stars avoids $27,000 in building alteration costs

We were recently referred a client who was having difficulty getting a Building Solution for their new home in South East Queensland. The 330m² two–storey house on a 10m by 30m footprint with a long span of windows facing East-West only achieved a NatHERS star rating of 2½ stars—way below Building Codes Queensland’s minimum energy efficiency rating of 6 stars.

Achieving 6 stars required expensive additions

The design has a 29% glass-to-floor ratio with tinting on half the glass, good cross-flow ventilation, ceiling fans throughout, and good insulation to roof, ceiling and walls. With the low cost energy efficiency features already in the design, we realised that getting a Building Solution using the star rating method of assessment was not going to be easy. An Acceptable Solution was to increase the star rating to 4½ and use credits of 1½ stars to reach 6 stars. This could only be achieved by adding 1kW capacity solar photovoltaic panels (not cost-effective with the roof pitch facing East-West) and installing high performance glazing or reducing the glazed area of the building. All expensive options for the client.

Glazing lowers star rating

Glazing on East-West facing walls dropped the NatHERS star rating to 2½ stars, way below the minimum energy efficiency rating of 6 stars.

Alternatives to Deemed-to-Satisfy gave a better result

An alternative approach was to assess the building according to BCA2010 Volume 2 Verification Method V2.6.2.2, listed as Acceptable Solution A1(1)(b) of the Queensland Development Code MP4.1 – Sustainable Buildings. This method is effectively three separate assessments:

  • Perform the NatHERS assessment for the proposed building;
  • Design the Reference Building insulation, ventilation and glazing to comply with BCA2010 Part 3.12 DTS; and
  • Perform the thermal calculation for the Reference Building to determine the Cooling Energy Allowance.

By applying a method that assessed the building as a whole, it achieved a calculated Cooling Energy allowance of 37.1MJ/m² compared with the Reference Building of 38.3MJ/m². So we had a Building Solution according to Verification Method V2.6.2.2. and the proposed building design needed no alterations to comply.

Assessing the building as a whole achieved certification without expensive alterations

With our solution, the client avoided alterations costing more than $27,000 and the anxiety of changing their dream design.

Our knowledge of Queensland Development and National Construction Codes and our experience with alternative energy efficiency assessment methods enabled us to deliver a 1500% Return On Investment for the client.

If you have any questions about how alternative assessment methods can be used to certify your design, contact us. We’ll be happy to answer any questions.

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