Environmental Impacts of Multi-Storey Buildings Using Different ...

- 98 -Note that whilst the utilisation of timber waste after deconstruction (of buildings) by burningfor energy production is not widely available in NZ at present (see section 8.6), it is importantto consider a future scenario where timber waste could be better utilised. The type and levelof treatment of timber both during its initial processing (and manufacturing if applicable) andduring its lifetime could have a great effect on the suitability and, therefore, possibility ofutilising deconstruction waste at the end-of-life of a building. It is certainly thought prudentto avoid CCA (copper-chrome-arsenic) treatments wherever possible.Appropriate design of the buildings, the suitability of proposed products and awareness ofdurability are all extremely important to ensure the longevity of the timber-based buildings.Building design considerations ensure that structural LVL components are not exposed todamaging deterioration during the proposed lifetime of the buildings.In keeping with current best practice, Warren and Mahoney advise that the use of CCA(copper chrome arsenic treatments) are to be avoided and, as such, wherever possible, thearchitects have avoided specifying CCA for any of the TimberPlus buildings components.Instead, products have been specified which have less potent ACQ treatments (or Borontreatments for lesser exposure areas, as defined by the NZBC, and Shadowclad is pre-treatedwith H3.1 LOSP azole). ACQ is a waterborne, Alkaline Copper Quaternary preservativesystem developed to provide long-term protection to wood exposed in exterior applications.ACQ is based on copper combined with a quaternary ammonium compound and is applied towood by pressure treatment. Copper and quaternary ammonium compounds are effectivefungicides and termiticides. Together they provide protection against a broad spectrum ofdecay fungi, borer and termites. ACQ can be used in all locations that CCA would previouslyhave been specified except H6. Wherever treatments are not required by code they haveavoided them.Cedar – used externally for both window framing and louvres – requires adherence to a strictmaintenance schedule. The Warren and Mahoney report notes that “with correctmaintenance of surface finishes, cedar is expected to last well in excess of the 60 yearbuilding lifespan”.The TDA Flatline Board System, proposed as the external cladding for the TimberPlusbuilding, is a theoretical system which has been designed for P. radiata. There are manyexamples of well designed NZ buildings constructed from P. radiata weatherboards whichhave lasted well in excess of 60 years – the key is the maintenance of the coatings and thebuilding’s design avoiding the creation of enduring damp conditions. As advised by Warrenand Mahoney Architects (Iain Nicholls, pers. comm.), it is expected that the TDA systemwould be no different.Similarly, Shadowclad plywood pre-treated to H3.1 with LOSP azole, also proposed forexternal use in the TimberPlus building, is designated to last 50 years when properlymaintained (Pers. comm. between Carter Holt Harvey and Iain Nicholls) and it was furtherconfirmed that that there would be no reason to expect any failure during the life of a 60 yearbuilding if properly maintained.