This Digest describes a target-based method of assessing the likely energy efficiency of a non-domestic building design. It is referenced in the 2002 edition of Approved Document L2 of the Building Regulations which includes a simple assessment method to address the design of air conditioning and mechanical ventilation systems. This Digest extends that method to include heating and lighting design. Both methods have been developed specifically for office building services design, and to address carbon emission as a Carbon Performance Rating. Calculations using this Digest's methodology can take into account heat recovery, thermal storage, heat pumps, chp systems, and renewable energy sources. Sample assessments for a mixed-mode building using multi-split cooling units and mechanical ventilation or an air-conditioned building using chilled ceilings and displacement ventilation are given. 12 pages.