This paragraph discusses the design and construction process related aspects necessary to answer the research sub-question:
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How can the design and construction process be analysed?First, an appropriate sequence for the design and construction process needs to be defined. The different steps of the cladding supply chain are extensively discussed by Ledbetter, for example (Ledbetter, 2003). Here, the term cladding includes non load-bearing façades. A flowchart for rain screen cladding design and procurement from design to installation was drawn by Kalian (Kalian, 2001). Whereas these papers provide a lot of detailed information, they focus on managing the supply chain and not primarily on construction itself. It also does not include the phases after the installation of the façade.
Based on this and on the experience of the author as a facade designer in Germany and The Netherlands a general sequence of eight steps has been identified. The façade design and construction phases run parallel to those of the rest of the building.
Even though these steps can differ slightly, the process is basically the same in most countries.
These steps are forming the structure on which the interview is conducted and the sequence was accepted by all interviewed parties.
System
Manu-facturing Assembly Use End of Life
Figure 16
Design and construction phases of curtain walls
Theoretically, the process is linear, but in practice there is a back-coupling between the phases. During the design process, for example, it might become apparent that the list of desired functionalities has to be adjusted. Results from the execution design (e.g.
Final material choices or detail geometries) often require a rethinking of architectural design implications a.o.
As the 8 phases form the backbone of the interview it is important to provide a brief explanation of each.
§ 2.2.1 System design
Façade system design is done prior to the actual design process. Systems are
developed by system providers, anticipating market needs. Systems need to meet legal requirements as well as the requirements from architectural design.
§ 2.2.2 Pre-design/development
In the pre-design phase the basic requirements for the building are being defined. It begins with a market survey and feasibility study. The location, size of the building, the type of use as well as legal requirements lead to a first definition of functional requirements for the façade.
§ 2.2.3 Architectural design
The architectural design phase is further subdivided. It usually begins with a design sketch which is then worked out further. At some point, drawings are made for the building permit; and based on these, the architect’s working drawings are developed.
This process requires continuous calibration with the development of the other crafts. It must be mutually agreed upon with the client; costs have to be calculated.
Depending on the project, structural or façade engineers are involved as well as climate designers. These phases are reflected in the specifications that describe the architect’s/
engineer’s work. Depending on regional procedures or the type of tender, the façade builder might or might not be involved in different stages of this process.
§ 2.2.4 Execution design
To a large extent, façades are standardised products; partly due to their responsibility for the building performance Water/wind tightness and thermal performance of the construction have to be guaranteed, which can only be achieved by tested systems. In contrast, a concrete wall is composed of cement aggregate and steel reinforcement and is designed according to the particular needs of the application. Architect and structural engineer create the plan after which the builder will directly execute the structure.
During the execution design phase, the builder has to execute a number of internal design steps to be able to conduct the job. These are based on the working drawings of the architect; however, the level of detailing exceeds the planning ability of the architect. Very often, the decision about which system is ultimately used is made at this stage.
Later on, the design phases with their complex embroilment will described be in more detail in chapter 3.
§ 2.2.5 Production
The production of façades is a process with high logistical effort. The façade builder receives profiles and fittings from the system provider. These are cut and milled and then sent out to be coated. It is interesting to know that coating is a delicate matter.
Typically, all elements of one colour are coated in one charge, because the next batch might show slight differences in colour and surface quality. Such aspects show that at this stage of the process changes in design are virtually impossible, and if done cause tremendous logistical effort. Therefore, this is the point when the design gets “frozen”.
Numerous subcomponents such as sun shading devices or glass panes will have to be designed, ordered and integrated in the production process. Depending on the production facilities, the builder will try to manufacture and pre-assemble as much of the construction as possible. The factory offers dry and clean conditions. The quality is easier to monitor than on the site, and mistakes can be compensated with all tools and spare parts at hand.
§ 2.2.6 Assembly
One can say that the more complex a system is or the more complex systems become in the future, the more inevitable pre-manufacturing and pre-assembly becomes.
Today, more and more unitized systems are preferred to curtain walling systems, especially for large buildings with a great number of repetitions, although the material and production costs are considerably higher.
Finishing the façade is an important step in the overall construction process of a building. At this moment, all interior work can be executed independently of the weather; an important factor concerning the time schedule. Weather conditions pose a potential threat for the assembly of the façade. This risk can only be reduced by minimising construction time onsite. This does not only require skilled personnel, but also a products aiming at fool-proof assembly, which is difficult with increasingly complex constructions. At the same time, the façade has a lot of complex interfaces to other disciplines. The construction times for buildings become increasingly shorter;
and very often production has to begin before measurements of the primary structure (concrete, steel) have been taken. The primary structure has to be finished in time for the façade to be installed. The tolerances are often in the range of centimetres, whereas façades allow no more than a couple of millimetres. Interior finishing touches the façade area, and there is a constant risk that the façade gets damaged by follow-up disciplines. In spite of these uncertainties the façade quality has to be according to plan; for example, because the sound absorption between rooms depends exclusively on the connection between dividing wall and façade, and the same is true for fire
protection. The façade as part of a networked climate concept creates another difficult interface to building services components.
Of course all of these parameters need to be considered in the preceding phases.
Figure 17
Unitised façade elements as delivered to the site Figure 18
Assembly of unitized façade system from the inside Figure 19
Assembly of a curtain walling system with scaffolding
§ 2.2.7 Use
This phase shows whether the façade matches all desired functionalities. A failure in comfort performance is directly observed by the user. The energy performance will be reflected on the energy bill. Monitoring is an important issue that grows with increasing complexity and the combination with building services installations. The responsibilities in case of failure have to be clearly stated. Maintenance and cleaning are considerable costs issues that must be accounted for in the early design phases.
They depend on material and detail choices as well as on accessibility of the façade.
Cleaning machinery such as cranes, lifts or ladders have a considerable effect on the architectural design. They are expensive and the question is what investment should be done beforehand to prevent high cleaning costs.
§ 2.2.8 End of Life
In former times, not much thought was spent on the end of life scenario of buildings, and façades in particular. In order to create energy neutral buildings recycling or reusing components is becoming a crucial issue A sustainable approach requires a concept for the end of life phase which needs to be developed in the phases from architectural design to assembly. Ideally, the components can be completely reused.
But practice shows that this is hardly possible, because façades that where built 30 years ago do not fulfil today’s requirements in terms of thermal insulation. In most cases this results in the need to exchange the entire system.
It becomes apparent that building a façade that lasts a very long time is the right strategy. Thereby it is important that the construction matches the type of use and the functionality of the building. Long lasting qualities can also be obtained by designing the façade in such a way that it can adapt to different uses. This way it can promote a second life of a building that is transformed from office building to dwelling, for example.