The art of progressing from complex problems to simple solutions has been regarded as the ideal approach to design ever since Mies van der Rohe’s famous “less is more” concept. For decades, the equation ‘reduction = elegance’ has remained largely unquestioned among architects. Now, however, advocates of sustainable building are making themselves heard, stating that architecture can only be fit for the future if its designers are guided by certification systems that encompass long lists of detailed criteria. Who would not be overcome by doubt in such circumstances?On the other hand, there are the calls from those who are convinced that only one single solution is required. For example: build passive houses, so that one can do without heating systems, or, building insulation is superfluous, highly efficient heat pumps will do the job just as well. Still others believe that one shouldn’t bother with the improvement of individual buildings and that a solution can only to be found in large-scale energy concepts that encompass entire city districts.Most of these ‘either-or’ strategies have two aspects in common: namely, they appeal to those who are primarily interested in saving time, money and effort; and, more often than not, they fall short of what is actually needed. Sustainability does not need cherry-picking and one-sided optimisation, but rather a culture of feisty ‘as well as’, multi-pronged solutions. Thus, we need building insulation as well as renewable forms of energy, refurbishment of old buildings as well as energy-efficient new buildings, solutions on the level of individual buildings as well as on the city district level. We need to face up to the undeniable fact of climate change whilst still offering occupants the comfort they need. However, we must occasionally also pose pertinent questions: How much comfort and how much living space per person are really required. How many vacant office buildings should be acceptable? When would the avoidance of building at all be the most sustainable solution?In brief, sustainable building is (unavoidably) a complex affair; Detail Green aims to mirror this great complexity. In this issue, there are articles on building insulation as well as on energy strategies for entire city districts; we report on the renovation of old buildings as well as on new buildings and the combinations of old and new. In this manner, we are attempting to do justice to the diversity and enormity of today’s building challenges and to the overarching questions of sustainability.