Process and Construction Cost

Published: 04 April 2011 / Amendment 1 / BCA 2011

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

5-STAR DTS VERSUS 6-STAR MODELLING

For this project, the Baseline House (see Sidebar Note) cost used was the 5-Star DTS compliant sales price (as of early 2010) provided by each of the participating builders.

Process cost reviews the likely building process changes that will be required to shifting from DTS to Modelling based assessment.

Construction cost measures any additional material and labour required for Baseline Houses to achieve a minimum 6-Star rating. Project research suggests this is likely to be affected by design and construction decision-making. The Project Outline (see Sidebar Note) nominated the material upgrade options and the sequence in which they were to be used. Assessors were then asked to determined the best use of those materials (extent, location etc).

Note: this project only investigated construction and process costs related to Modelling part of BCA 2011 Part 3.12 Energy Efficiency compliance. There may be other costs related to the Acceptable Construction Practice provision that can be extra over to Modelling outcomes.

• Modelling software cost – this project has not investigated process costs related to purchase, training, licence renewal, local technical support and the like. An indicative “performance” comparison was undertaken (see below – Like for Like Comparison).
• Verification or Assessment – project findings suggest better construction cost outcomes will be achieved using an assessment rather than verification based process. Whilst assessment may add Modelling costs (done earlier in the process, hence more frequently), research suggests this cost may be off-set by downstream construction cost savings.

• Material and labour costs – builder purchase costs vary. Participating builders provided current rates to upgrade and/or supply and install a range of materials (see Sidebar Note). A nominal “builder’s margin” was then added to these costs so that the reported construction cost would reflect the likely change in sale cost. The “marked up” rates were then used to determine an indicative local practice cost for each of the materials investigated. Reported costs are only intended to compare material types so as to inform performance based decision-making.
• Worst-case orientation – the extent of Baseline House performance improvement required to achieve 6-Star is based on the worst-case orientation. For worst-case orientations, costs are based on the nominated extent of material and the rate to install. For best-case orientations costs are a conservative estimate (cost could be less) based on the best to worst performance gap. Case by case outcomes will vary depending on actual orientation.
• Orientation frequency data – creating a database from past house orientation outcomes (sit plan bearings) and recording ongoing sales data is likely to identify a “most frequent” best and worst-case orientation outcomes. This would inform builder “80/20” costing strategies.
• Adoption curve – it is likely that, as local practice shifts to Modelling based assessment, better design and construction outcomes will emerge – there will be a “bell curve” cost effect. Cost initially be higher and then reduce as cost efficiencies of supply and installation come on stream (in 2003 when ceiling insulation became common practice, insulation costs reduce as supply volumes increased).
• Purchase value – Modelling allows for the measurement of the thermal performance contribution of what to date have been “similar” materials. Construction data shows a performance gain when Baseline House worst-case local practice glazing performance is compared to best-case local glazing performance (see Sidebar Note).
• Houses 19, 20 & 22 – these houses report a high than actual cost because standard glazing was used for Baseline House Modelling even though 5-Star DTS compliance required the use of low-e glazing.

Click the link below to download the full text version of the Local Practice Note: Process and Construction Cost

Building Professional Registration or Login Required

To download the file process-and-construction-cost-amendment-1.pdf you need to login to the As-Built Learning Exchange. If you are a Building Professional and you do not have login access, you will need to register.