Australian Standard 3959:2018, Construction of buildings in bushfire-prone areas, states that in BAL-29 areas "those parts of handrails and balustrades that are 125 mm or more from the building have no requirements" (clause 7.7.4). Therefore LOSP-treated pine would be OK. The guidelines on the use of LOSP in Timber Queensland's Technical Data Sheet no. 24 may be helpful. It can be downloaded here: http://www.tpaa.com.au/TPAA/wp-content/uploads/2015/06/4_5_5_0-Recommendations-for-use-of-H3-LOSP-pine.pdf. If any part of the handrail or balustrade is less than 125 mm from any glazing or any combustible wall, that part must be non-combustible or made from one of the seven timbers classed as 'bushfire-resisting'. LOSP-treated pine would not comply for that part of the handrail or balustrade.BAL-29
Answered on 13-01-2021
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