A new themed issue of the ICE Engineering Sustainability journal includes the best papers from the proceedings of the fourth international conference on the Zero Energy Mass Custom Home (ZEMCH) network, which was held in Lecce, Italy in 2015.ZEMCH conferences bring together researchers and government and industry professionals to discuss the problems and delights of design, manufacturing and marketing surrounding the delivery of low-carbon dioxide and, ultimately, zero-energy houses that are customisable on a mass scale, either built or under construction in developing and developed countries. Founded in 2010, the ZEMCH network network now has 667 global partners from academia, industry and government based in over 45 countries.The papers cover key research topics in the areas of sustainable built environments, including green building rating systems, intelligent building technologies, gamification in the built environment, four-dimensional (4D) building information modelling (BIM), vertical green walls and building-integrated photovoltaics (BIPV).Green building ratingA wide range of ‘green’ building rating and assessment tools are used around the world to help mitigate the environmental impacts of the built environment through the measurement and recognition of sustainability performance (AlWaer and Kirk, 2012; Haroglu, 2013). Sustainability is now a top priority in the Middle East region and countries like Jordan, Qatar and UAE have developed their own green building rating system to incorporate social, economic, environmental and cultural aspects in modern construction.Shareed and Altan (2017) assessed and compared the different building sustainability rating systems in the Middle East with well-established and leading international green building certification systems such as the Building Research Establishment environmental assessment method (Breeam) and Leadership in Energy and Environmental Design (Leed). The assessment focused on the vision and structure, categories, weightings, levels and certification processes. The study highlighted the importance of developing and employing local green building codes or systems to achieve sustainability targets according to national priorities and regulations.Gadakari et al. (2017) focused on finding the relationship between building intelligence and sustainability by developing a predictive statistical model that can estimate the impact of intelligent building technologies (IBTs) on sustainability scores of green building rating tools. The data were collected from 40 Breeam- and Leed-certified buildings in the UK and Europe and were subjected to qualitative and quantitative analysis methods. The work highlighted the numerous benefits that IBTs can provide, and the analysis proved that there was a strong positive correlation between the number of IBTs used in a building and the scores achieved.Understanding the energy gapOne of the most important challenges faced by the building sector today is tackling the ‘energy performance gap’, which is the disparity in energy use of buildings, from predicted performance at the design stage to actual performance in use (Baborska-Narozny and Stevenson, 2017; Johnston et al., 2015; Robinson et al., 2016). Patlakas and Raslan (2017) discusses the significant role of building users in determining the energy use of buildings and the influence of their behaviour on the ‘performance gap’.The authors attempted to address the issue by using ‘gamification’ or game-based tools to help users better understand the issues relating to building performance, post-occupancy evaluation surveys and facilities management. The study demonstrated both the advantages and challenges of gamification which were in agreement with the experiences reported in the literature.Retrofitting of existing buildings offers significant opportunities for reducing global energy consumption and emissions (McGrath et al., 2013). Retrofit projects present many challenges for managers and decision makers, particularly when the end users remain in the building over the period when the works are carried out and are disrupted by the retrofit process.Chaves et al. (2017) discussed the potential of using 4D BIM to support better planning of construction works and reduced disruption to end users in retrofit projects while delivering energy-oriented and cost-effective solutions. The work developed recommendations detailing the steps to be undertaken by decision makers in evaluating retrofit scenarios in situations where the dwellings are in use during the retrofit works.Green walls and photovoltaicsDuring the last decade, the presence of green walls or vertical gardens in building designs has increased, providing several benefits to the urban environment including reduced energy demands of the buildings’ cooling systems, mitigation of the heat island effect and improvement of the thermal performance of buildings (Coma et al., 2017).Vox et al. (2017) carried out field tests to investigate the effects of two types of green vertical passive systems on building walls in the Mediterranean region. Several climatic parameters concerning the walls and the ambient conditions were analysed to estimate the variations in the surface temperature of walls equipped with the greenery systems. The effective thermal resistance of the green layer was evaluated as a useful tool for models to estimate internal climate and energy fluxes.During the last 15 years, double-skin facades (DSFs) have become an increasing and vital element in the built environment, particularly in combination with integrated photovoltaic (PV) panels. By simultaneously functioning as envelope material and power generator, building integrated photovoltaic (BIPV) systems can be more cost-effective and can provide savings in materials and energy costs, reduce carbon dioxide emissions and add architectural enhancement to the building (Agathokleous and Kalogirou, 2016).Yu et al. (2017) investigated and compared the energy and thermal performance of a building with a glass DSF and a PV-integrated DSF through dynamic simulation modelling. The results showed that the PV-DSF system was advantageous during summer to decrease cooling load. The building energy consumption of the PV-DSF decreased by 15% compared with the glass DSF. Furthermore, 1438 kWh of electricity was generated, which corresponded to about 18% of the annual building energy consumption required.The themed issue disseminates up-to-date research on sustainable built environments and I hope readers are inspired by the papers to contribute new knowledge in the field.