There are numerous strategies available to design and construct a low energy or nearly zero energy building (NZEB). However, the design strategy for a building depends on a high number of factors including location, climate, cost, available resources, etc. For instance, for countries like Ireland, which have a temperate oceanic climate, a key to achieving NZEB is a high thermal and air tightness performance of the building envelope, installing highly efficient space and water heating systems, and utilising renewable technologies for energy and heat generation. The challenge is to find the best combination of design strategies that would tackle the energy performance problems of a particular building. For example, is it better to design a super-insulated building with minimum heating requirements, or provide less insulation but install a large amount of renewable energy sources? This paper presents the outcomes of a number of case study buildings in Ireland, which focus on the life cycle cost and environmental analysis (using energy and global warming potential as indicators) of NZEBs using various heat sources, such as a gas boiler, biomass boiler, a domestic gas fired combined heat and power unit, heat pump and renewable technology. With the de-carbonisation and increased efficiency of the electricity grid, the low global warming potential (GWP) emissions of biomass fuels and the depletion of fossil fuels, future buildings should be (i) designed and constructed to be super-insulated with high air-tightness performance resulting in minimum heating requirements and (ii) operate with heating systems that have low impact on the natural environment, such as a biomass boiler or heat pump. (C) 2017 Elsevier B.V. All rights reserved.