Roof cladding tool for cost and environmental impact

By - , Build 124

What is the cost of a roof cladding over its life? What is its environmental impact? The BRANZ website has a spreadsheet tool that has the answers for residential claddings.

Figure 2: Roof cladding scores with zero weight costs and equal weights for all environmental impacts – a lower score is better.
Figure 1: Roof cladding scores with equal weight for costs and environmental impacts – a lower score is better.

The BRANZ Roof claddings life cycle analysis tool is a spreadsheet that provides the initial cost of the roof area in dollars per square metre ($/m²) and the annual cost for the life of the cladding. Users can combine costs with environmental impacts by giving weights to each attribute. The tool gives a net score on a scale of 0 to 100, and the results enable a ranking for various claddings.

Using the tool

There is no right answer or solution using the tool because each user will have different preferences for cost, environmental impacts and aesthetics. Figure 1 shows one trial using five different claddings and an even weighting between environmental impacts and costs. Initial cladding costs are amortised over the life of the cladding using a discount factor. Maintenance costs are also included over the life of the cladding.

The chart indicates concrete tiles and prepainted corrugated sheet steel have the lowest or ‘best’ scores for the selected combination of weights and discount rate (5%).

Environmental impact

The tool considers three aspects of environmental impact – embodied energy (EE) in initial manufacture and maintenance, carbon dioxide releases during manufacture and an assessment of recyclability of the material. Figure 2 shows the same claddings as Figure 1, but with zero weight given to costs and equal weights given to each environmental impact. For this example corrugated steel, metal tiles and concrete tiles score the best.

Figure 1: Roof cladding scores with equal weight for costs and environmental impacts – a lower score is better.
Figure 2: Roof cladding scores with zero weight costs and equal weights for all environmental impacts – a lower score is better.

For more

The Roof claddings life cycle analysis tool is available as a free download from the BRANZ website www.branz.co.nz, then select Toolbox. The tool can be used to conduct trials and compare different claddings that are being considered for a project.

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Figure 2: Roof cladding scores with zero weight costs and equal weights for all environmental impacts – a lower score is better.
Figure 1: Roof cladding scores with equal weight for costs and environmental impacts – a lower score is better.

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