Balancing Design and Performance in Building Retrofitting
– a Case Study Based on Parametric Modelling



ABSTRACT

Retrofitting the existing building stock will become one of the key fields of action for architects in the future. Due to the
raised awareness of CO
2
emissions related to energy consumption of buildings, architects have to increasingly consider
parameters influencing the energy performance of their retrofit designs. This is a complex task especially in the early design
stages as multiple dependencies between building form, construction and technical systems influence overall energy
performance. The inability to cope with this complexity often leads to simplified solutions such as applying massive
insulation on the outside, neglecting aesthetic expression and design flexibility. Digital models storing multidisciplinary
building information enable the inclusion of performance parameters throughout the architectural process. Besides the
geometric parameters constituting the building form, semantic and topological parameters define building element properties
and their relations. This enables an integrated view on the building. We present a case study utilizing parametric façade
elements within a building information model for an integrated design approach. The case study is based on an existing
retrofit project of a multi-family house with very poor energy performance. Within a design workshop a parametric building
model was used for the development of the designs. An integrated analysis tool allowed an immediate performance
assessment without importing or exporting building data. The students were able to freely define geometric and performance
parameters to guide their design solution. Balancing between formal expression and energy performance lead to integrated
design sketches, resulting in surprising solutions for the given design task.

Keywords: building information modelling, building performance, parametric design

INTRODUCTION
In European countries, the retrofitting and renovation of the existing building stock will become the key area of
work for architects as the amount of building retrofits increases continuously [1]. Today’s main drivers for
retrofitting are environmental issues. Due to the raised worldwide awareness of CO
2
emissions related to energy
consumption of buildings, architects have to increasingly consider parameters influencing the energy
performance of their retrofit designs. The traditional view on how to cope with environmental issues in buildings
is still often very limited. In this view, the energy performance of buildings is considered in opposition to the
freedom of aesthetic expression. Some of the realized so-called ecological buildings denote the other extreme,
promoting excessive formal and material measures to achieve sufficient building energy performance.
The current architectural design process lacks the necessary integrated view on the building. Due to the
complexity arising from multiple dependencies between form, material and technical systems, an integrated view
of the building can only be achieved by utilizing computational tools and methods [2]. The method of building
information modelling resembles one recent approach to capture these manifold dependencies by adding
parameters to define the building components more closely. Geometric, topological as well as semantic
parameters are stored within the building model which therefore acts as a data repository [3]. The neglecting of
the multiple dependencies between form, material and technical systems often leads to simplified answers such
as applying massive insulation layers on the building envelope. Due to conservation aspects and unsatisfying
visual appearance this is often not suitable for retrofitting purposes. No tools are available to support an
integrated view on a building design from the important early design stage on. Tools analysing energy
consumption and other environmental criteria such as simulation software are mostly applied after the initial
design phase, thus not influencing design decisions made during the early design stages.
We present an approach utilizing parametric facade components for integrated design sketches.
Multidisciplinary criteria such as geometric parameters, topological dependencies and physical performance
parameters are used to define the designs, modelling form and energy performance as equal stakeholders in the
design process. An especially developed tool utilizes the multidisciplinary information stored in the building
information model to execute real-time energy performance calculations. Within a conceptual workshop,
students explored the capabilities of multidisciplinary parametric design. Utilizing a digital building information
model from the beginning on, students were able to develop unique answers to the given retrofit design task.

Retrofit design task
The design task for the students workshop was the retrofitting of an multi-family house in Zurich, Switzerland,
built in 1931. The age and condition of the building is exemplary for many buildings in Zurich. Built with
simple, massive walls without any insulation, its primary energy consumption is excessive. 21.000 litres of oil
are required for the heating and domestic hot water per year. Obviously, there is a huge potential to increase the
energy performance.


Figure 1: Existing building

Due to the building owner, a non-profit organisation for affordable housing, concepts for the retrofitting had to
consider the aesthetic expression of the façade as well as the economic impacts of retrofitting measures. Within
the one-week design workshop, students were asked to redesign the building envelope as the most important
interface between architecture and energy performance. After discussing and developing the concept for the
technical infrastructure inside of the building, the students were asked to develop an architectural concept of a
retrofitting of the building envelope. In their approaches they were supposed to consider performance parameters
equally to geometric/aesthetic parameters, to balance measures of form, construction/material and technical
infrastructure systems.


METHODS

Retrofitting for CO
2
-free building operation
The concepts for the technical infrastructure for heating, ventilation and lighting were laid-out with the students
at the beginning of the workshop by developing schematic sketches of the infrastructure systems. The aim was
the CO
2
-free operation of the building, not permitting the burning of fossil fuels inside of the building. The
existing oil burner was supposed to be replaced by an efficient heat pump, utilizing the potential of the heat
stored in the ground for the generation of heating energy. Due to the efficiency of the thermodynamic process of
the heat pump being highly dependent on the heating systems inlet temperature, the overall heating system has to
be designed to enable an inlet temperature as low as possible. The existing heat distribution system of pipes and
the emission system of radiators were supposed to remain. Therefore, in order to run the heating with a low
temperature of 28° C, the transmission heat losses of the envelope have to be low. Otherwise the small
distribution area of the radiators would not be sufficient to cover the heat losses and thus to heat the rooms.
Therefore, realizing an energy efficient, CO
2
-free operation of a building is dependent on the layout of the
technical systems but also on the energetic performance of the building envelope. The building envelope consists
out of façade, roof and floor to ground. For the design workshop, the students were asked to redesign the façade
as the most important interface between architecture and building performance.