Densification and retention

Dealing with historically significant examples of residential housing

Housing developments from the post-war period are in the spotlight. More living space needs to be created in cities, which increasingly places a question mark over old structures. Stefan Kurath and Simon Mühlebach from the Institute of Urban Landscape at the Zurich University of Applied Sciences (ZHAW) have researched the issue of dealing with historically significant examples of residential housing.

The socio-political demand for development internally is putting the focus on residential housing from the postwar period. Their age means they are in need of renovation and their floor plans no longer reflect the current requirements of living spaces. At first glance, replacing the old buildings with newbuilds seems the obvious choice. At the same time, the abundance of green space makes densification measures in the intermediate and access areas enticing. Larger plot areas are mostly the reserve of the same property developers. Even if a housing development has been recognised as historically significant in the meantime, they have sometimes not yet been entered into the heritage inventories.

Why renovate?
There are a range of arguments in favour of the conservation of these buildings. For instance, housing development structures have significance in terms of social history and building culture, making them important witnesses of the urban development considerations and housing construction subsidies at the time on greenfield land, mostly on what were the outskirts of the city. In terms of their dimensions and quality, the housing developments and districts are comparable to other city expansions, such as those in the 19th Century. The structure of the free space and the landscape architecture was accorded particular importance at that time and was considered to be a guarantee for a high standard of housing. Building on this today would noticeably disrupt the entire spatial experience and quality of the free space. The rationale against the replacement of the old buildings with newbuilds is the fact that the latter often have fewer residences per area than before, despite the building being larger, as the living space requirements per person have considerably increased.
Densification through upwards expansion. Upwards expansion allows the large areas of trees and shrubs to be retained. The spatial proportions and shading of the free spaces change (Bebelallee housing development, Hamburg, Germany).
A solution involving a replacement building also often results in the residents being forced to leave the district, because they cannot find a replacement due to inadequate phasing within the development or are unable to afford the new properties. These considerations make it clear that strategies need to be found which strive to strike a balance between densification and renovation – in favour of retaining achievements in building culture as things that are worth remembering. To this end, we at the Institute of Urban Landscape have examined different residential developments in Switzerland and Germany with regard to the balancing act between retention and densification as part of a research project funded by the Foundation for Monument Protection (see publication by Anke Domschky, Stefan Kurath, Simon Mühlebach, Urs Primas, Densifying urban landscapes. Strategies for renewing the cultural building heritage of the post-war era, Triest Verlag, Zurich, 2018). This showed that there is in fact potential for densifying housing development structures of the post-war era if cultural building heritage is taken into consideration.

Strategies promising success

Two urban design strategies have proven themselves to be particularly successful in the past. On the one hand, the discovery of weaknesses generally leads to interventions which contribute to a clarification and strengthening of the original urban development concept. This affects structural, typological and design aspects, especially on the outskirts of the developments as well, which mostly become modified over time. Here, replacement newbuilds or extensions are perfectly feasible, while the more sensitive components of the housing development and free spaces are renovated.

On the other hand, renovating, adding to or extending the inherent structural logistics of the existing development has also proven to be beneficial. An important prerequisite for success in this regard is to raise awareness of the issue among everyone involved in the planning. Intensive cooperation at the earliest possible stage between the client, architects, landscape architects and those responsible for the preservation of historical buildings and gardens is imperative here.

The process of competing for tender has also shown itself to be particularly suitable for exploring the range of densification options, if the aim is for all those involved to implement the best solution and not just the first good idea that comes along. It is worth the effort, because taking into account the cultural building heritage – quite apart from whether or not a building is worth protecting – helps to endow the housing with greater substance in terms of building culture, urban development and atmosphere, thereby making it a more pleasant environment to live in. This is in the interest of the residents, owners, property managers and investors.
Densification through upwards expansion and with newbuilds on the outskirts to clarify the urban transitions (Altenhagener Weg housing development, Hamburg, Germany)..
Image sources: Simon Mühlebach, Zurich
Densification through upwards expansion and renovation of the existing building in order to retain unique structural features (Irchel retirement homes, Zürich, Switzerland)..