This Recommendation provides a consistent framework for building owners, managers and operators to critically assess, score and improve the sustainability performance of office buildings in ten key areas; Energy, Water, Air, Comfort, Health & Wellness, Purchasing, Custodial, Waste, Site, and Stakeholders. The framework described in this Recommendation provides a set concrete and measurable steps to reduce the environmental impacts, and specifically the Greenhouse Gas emissions, of existing office buildings, thus contributing to the achievement of the Sustainable Development Goal 11 'Make cities and human settlements inclusive, safe, resilient and sustainable'. The Annex to this Recommendation specifically contains an assessment scoring methodology to allow owners and managers to undertake a self assessment to evaluate their building's current status and track progress going forward.