ONLINE BRUSSELS HERITAGE - ONE-DAY SEMINAR - 11/12/2014

process of overlapping the different territorial “tiles”.

URBAN FORM: REDUCING ENERGY CONSUMPTION IS PRIMARILY A TERRITORIAL CONCERN, NOTA BUILDING-RELATED ONE

Abuilding never exists as a separate entity. It is always one element in a larger-scale composition. As soon as it is designed, it is envisaged within and in relation to its environment (e.g. logic of sub-division, rationale behind the “greening” of urban spaces, etc.). The urban form enables us to easily document these elements relative to energy consumption and to draw out elements for analysis. An examination of building contiguity is interesting in this regard. Historically, in order to compensate for the absence of efficient heating systems, buildings were constructed adjoining each other. By grouping houses together in this way, heat loss surfaces were reduced, thereby also proportionally reducing energy consumption. In new, fully insulated buildings, this fact is less important. However, in old, non-insulated buildings, contiguity was already being used as an energy strategy. Any evaluation of the intrinsic qualities of a building, prior to any work, must take this essential fact into account.

Figure 2 illustrates the density of buildings over time in a series of seven housing blocks. A move away from contiguity and greater consumption of space can be seen. One of the historical reasons for this phenomenon is linked to the definition of a town as a place of exchanges, where the distances needed to be short to facilitate travel by foot or by horse. There was a historical benefit in the town being compact. This design is also valid for buildings. The more compact they are, the more “liveable” they become. Over time, with better heating systems and other modes of transport, towns began to spread out, consuming more territory. In the diagram, this is illustrated by a reversal of the ratio of open to built-up areas. The consequences of these changes were significant. In the 19th and 20th centuries there was a reversal in the amount of green spaces. This fact must be taken into account because when talking about urban heat islands, urban microclimates and summer comfort, we are dealing with an old and dense city. This means that in winter the energy consumption of a building is, theoretically, less significant than in peri-urban areas. However, when a thermal audit is carried out, the data used often to come from peri-urban weather stations, which can skew the initial calculations. For example, if the same weather file is used for calculations in a zone in Woluwe-Saint-Pierre and for another area in the old city centre, the errors will be more pronounced in the calculations concerning the area within the Pentagon (inner ring road) due

Fig . 2

Diagram of the historical evolution of building density. Over time, there has been a reversal of the ratio between built up and open spaces. A rapid increase in the consumption of regional space can be seen (© Apur).

26 | Urban forms, typology and improving the energy efficiency of old Brussels buildings