Reduction of the cost of construction is a constant goal for the building industry. One way of reducing the construction cost of buildings is to develop building technologies that will give increased productivity. Reduced construction time at the building-site and waste of materials and resources contribute to furtherreduction of the costs. This is why the sector is developing towards more industrialized construction methods with prefabricated components. The objective of this thesis is development of industrial construction methods forcost-effective and energy-efficient construction of multi-storey buildings. It is important to highlight the difference between cheap or low-cost and cost-effective production. It is possible to produce buildings to a low-cost at the expense of decreased quality and design. Conversely, cost-effective buildings are buildings that are produced to a low cost while maintaining a high standard of design and comfort. While cost reduction efforts are often made based on a, relatively, fixed building process, this research is focused on reducing the costs by changing the building process with the help of innovative building technologies. The construction of a building is a very complex practice with a wide range of interacting processes. The hypothesis is that a holistic approach is advantageous in order to find effective construction methods. To achieve a holistic view, an interdisciplinary approach to the research is required. By approaching the development of construction methods from the point of view of the entire building process, it is possible to achieve optimizations with synergy effects and by that find solutions that are time-efficient, energy-efficient and cost-effective at the same time.
The work started by analysing the building process and the construction methods currently used in order to; discover the most common problems, gain understanding of the strengths and weaknesses in the conventional construction methods and identify the fields where the largest potential for improvements existed. Based on this analysis, a new building concept for industrial construction of multi-storey buildings is formulated called The Symphony concept. The concept involves a holistic view of the whole building process and is based on a prefabricated heavy structure that is covered with a prefabricated building envelope consisting of large, light-weight elements with a high degree of prefabrication and finished exterior surfaces. The concept required development of new types of building-elements and assembly methods. The technology was first evaluated while still on the drawing table. Some of these evaluations have been of a more detailed character and are reported in scientific papers. Thereafter an experimental building in full scale was erected in order to test the developed technology during production and assembly, while measurements and tests were performed in order to evaluate the performance of the building in operation. Based on the obtained results suggestions for improvements could be given in order to upgrade the concept further.
The economic analysis of the building process showed that the largest cost posts in the construction of dwellings are the climatic shell (24 %), the interior finishing, and the management costs. The construction of the climatic shell is optimized through the use of the Symphony elements while the management costs are reduced through the use of prefabricated elements with a high degree of prefabrication which, substantially, increase the construction speed. Results show that it is possible to reduce the construction costs with about 25 % when constructing according to the Symphony concept compared to conventional construction methods.
The construction of the large light-weight Symphony-elements was possible thanks to the CasaBona system. CasaBona is a building system which integrates the thermal insulation with the structural elements in the outer walls by embedding sheet metal profiles into stiff insulation blocks. The results show that the strength of the profile, when embedded in rigid insulation blocks, is increased between 22 % and 33 % when submitted to bending forces, and between 161 % and 210 % when submitted to compressive forces.
Simulations of the annual energy use of buildings show that the energy performance of buildings is improved with increased effective thermal mass. Increased mass is also beneficial from the acoustic point of view. However, it is important that the interior space is separated from the exterior climate with constructions that have low U-values. It could be concluded that the most beneficial design strategy is the combination of a heavy core-construction (which has a large mass and thermal inertia) and a light-weight building envelope (which yields low U-value without adding to the thickness of the outer-wall).
The construction of the experimental building made it possible to test the technology in an inexpensive yet realistic way. However, it is important to bear in mind that the information which can be gathered from an experimental building can be limited depending on the size of the building and its finishing standard. It could also be noticed that industrial construction benefits from an interdisciplinary design process since this render the increased use of prefabricated components possible.
Stockholm: KTH , 2008. , xiv, 15-101 p.