On average, a building's façade is responsible for a third of its energy consumption. Therefore, taking the whole life cycle from construction to demolition into consideration, it is more favourable to give an old building a new façade than to construct a new building, concludes PhD student Linda Hildebrand.
Even replacing an old building with poor energy performance by a sustainable state-of-the-art building is less than advisable, at least when looking at it purely from the perspective of energy. That is because demolition and the new build process uses so much energy that the energy benefits of the new building are generally cancelled out. In any case, a different building construction would do little to change the overall energy performance, so why replace it? Demolition is an energy-consuming activity, while the manufacture and transportation of new materials and constructing a new building would cost a great deal more – just based on the fact alone that transportation takes place by means of diesel-guzzling trucks and limestone is excavated and cement clinker is fired in order to produce concrete. Therefore, stripping and improving the shell with smaller windows or with double/triple glazing will almost always be more favourable from the perspective of energy. ‘If the main supporting structure of a nineteen-sixties' building is sound, with ceilings of a sufficient height, then redevelopment – with improvement of the façade – is on average seven times more favourable than the option of demolition/new build when it comes to energy investment,’ calculates Hildebrand.
For her PhD research the specialist in sustainable building-constructions analysed 25 office buildings. In doing so, she mapped out where in each building the most energy is consumed, not just during construction, but in the course of the whole life cycle. It also brings to light why some buildings offer more potential for optimising their energy performance than others. A few rules of thumb: the ratio of surface area to volume has to be low, a light building concept is always more favourable than a heavy one, and a flexible layout makes the building more attractive for reuse.
Underground parking garages and other underground facilities are unfavourable from the perspective of energy, because they require complex structural interventions to prevent floors from rising. Therefore, if possible, a parking garage should be realised above ground. However, an attractive ground floor with facilities for shops and a well-designed outdoor space also determine a building's success. This is a typical example, therefore, of a recommendation that makes clear how complex it is to find a good balance. ‘The sustainability of a design is determined by the ratio between the quality achieved and the amount of energy needed for this,’ concludes Hildebrand. ‘And, of course, nothing lacks sustainability as much as an ugly, uncomfortable building that no-one wants to occupy.’