BRANZ conducted field trials in Rotorua to examine how metals degrade in geothermal environments. Different metals showed very different responses.
The scope of NZS 3604:2011 Timber-framed buildings requires a 50 m separation from geothermal hot spots. This will not always reduce corrosion rates to a safe range.
Wood discolouration is likely to be the result of copper sulphide forming on/in wood treated with copper-based preservatives.
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