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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. [ABSTRACT FROM AUTHOR]

• CLT building showed 30% less LGHGE compared with a RC building in Melbourne. • A reduction of 1.3% of LCC was observed for CLT compared with a RC building in Melbourne. • CLT building has an advantage in terms of LCC and LCGHGE in the construction/EOL phases, but not in the operation phase. • Energy efficient methods and reuse/recycling at EOL can enhance LC performance of CLT buildings. Engineering wood products have significant potential as a sustainable alternative for concrete and steel in construction. Cross Laminated Timber (CLT) can add value to conventional timber products due to its high strength-to-weight ratio, simple installation, aesthetic features and environmental benefits. Recent changes in the national construction code permit structural timber buildings with a height of up to 25m, which demonstrates the strong commitment of the construction industry to adopt more sustainable practices. This paper aims to compare life cycle greenhouse gas emissions (LCGHGE) and life cycle cost (LCC) of CLT and reinforced concrete (RC) in identical midrise residential buildings in three most populated cities in Australia. It has shown that the CLT building has 30 % less LCGHGE compared with the RC building over a life span of 50 years in Melbourne, and 34% and 29% reduction in LCGHCE in Sydney and Brisbane, respectively. The results from LCC analysis showed that CLT building is 1.3% lower than conventional RC in Melbourne, and 0.9% lower in Sydney and Brisbane. The initial and end of life phases reflected reductions in LCGHGE and LCC for the CLT building whilst the operation phase incurred higher values. The extended service life of buildings has a major impact on the operational phase while changes in the discount rate have strong effects on the lifecycle operational and maintenance costs. Overall the CLT building outperformed the RC building in terms of LCGHGE and LCC across three cities. However, further savings in the operational phase with energy efficient methodologies and reuse or recycling of timber products at the end of life of the building can reinforce CLT as a sustainable alternative to RC construction. [ABSTRACT FROM AUTHOR]