All Wood Window Alliance windows are made from timber legally sourced from sustainably managed forests and all members must hold either FSC or PEFC Chain of Custody certification (for more information see Wood Campus 'Procuring Sustainable Timber').
Wood Window Alliance windows are now recognized as a separate standard in BRE’s Green Guide to Specification:
Wood Window Alliance windows windows made to the standards required for membership of the Wood Window Alliance (e.g. TWA Scheme standards) have an A+ (domestic) and A rating in BRE's Green Guide to Specification. A report by Heriot Watt University on timber, modified timber and aluminium-clad timber windows shows how all the timber-based frames considered have significantly lower environmental impacts than PVC-U.
The Heriot Watt University report (Whole Life Analysis of timber, modified and aluminium-clad timber windows) demonstrated that wood window frames made to WWA specifications are carbon-negative over their overall life-cycle.
Each timber window installed instead of a PVC-U window was shown to save 160kgs CO2e over 60 years - that's over one and a half of a tonnes of CO2e per average house of 10 windows.
Modified timber and aluminium-clad timber frames are also carbon negative, saving approximately 140kgs CO2e over 60 years - that's just under one and a half of a tonnes of CO2e per average house of 10 windows.
The report concludes that all the timber-based window frame materials considered have a lower environmental impact than PVC-U alternatives on all but one environmental impact measure (the exception being ozone layer depletion) and in every End-of-Life scenario considered.