Buildings contribute around 45% of the world's energy consumption. Reducing energy demand in buildings therefore plays a vital role in addressing the depletion of energy resources and associated environmental issues. Previous research explored the optimisations of the costs and energy consumption of buildings, but often overlooked the connections, tradeoffs and synergies between them. The aim of this paper is thus to develop a theoretical model of the influencing parameters of the life cycle cost-energy relationship (LCCER) of buildings using the Political, Economic, Socio-cultural, Technological, Environmental and Legal (PESTEL) analytical framework. This study was carried out through a critical literature review, model development and validation through case studies with four zero or nearly zero energy building projects carefully selected from the European Union and Australia. The developed model addresses the buildings' LCCER by identifying the key influencing parameters and explicating the mechanisms (namely, the simultaneous and unilateral effects) by which the identified parameters affect such relationship. The important influencing parameters were found to reside in two aspects: (1) internal project designs covering building characteristics, building structure and function, and construction process, and (2) external environments covering climate, economic condition, occupant behaviour, policy and regulation, and buildings' lifespan focused in the studies. Various statistical correlations were found to exist between the costs and energy consumption of the studied cases. It is summarised that these correlations may be attributable to the synergy between the simultaneous and unilateral effects of the identified parameters. The developed model contributes a systemic approach to examining the building's life cycle economics and energy in a comparative manner.