In the last decade, more buildings than ever have been built, therefore, construction waste and CO2 emissions have drastically increased. The construction industry consumes the largest portion of material sources, and in exchange produces more than 1/3 of the total waste and CO2 emissions in European Union. In Denmark the construction industry produces around 40% of the total waste, while also being responsible for more than half of CO2 emissions. However, as the negative impacts rise, new approaches are needed for construction of residential buildings.
In general, there are two main methods to construct buildings - traditional on-site and prefabricated off-site method. Both methods have benefits and drawbacks, though it is unclear which method adapts better to the increasing construction waste and environmental impact problem. So, this master thesis provides a comparison between two types of prefabricated construction building complexes – concrete and timber – in connection to on-site construction method. The comparison between the prefabricated construction methods and on-site construction method is done for building waste quantities to see which construction type generates the most and least construction waste and which are the most frequently used construction materials. Then, an environmental impact measures are calculated through a life cycle assessment analysis for the most frequently used materials for the two prefabricated construction methods to identify which construction is more sustainable.
For the analyses, building material quantities from both prefabricated construction types are used as basis for further studies. The material quantities are estimated through building drawings, details, and material bills from the corresponding construction companies and from general building construction guidelines, material property specifications in Denmark. The information about construction waste quantities and waste sorting fractions is also acquired from the construction companies.
The waste analysis showed that concrete construction building complex generates less construction waste than timber construction building complex, 8.4% and 15.7%, respectively. The most waste for concrete construction is generated from combustible materials that are incinerated and concrete debris that is recycled. For timber construction the most waste comes from mixed materials that are recycled and wood that is also recycled. The on-site construction showed to have wide range of possible construction waste quantities, but generally 10% are accounted for it. So, the prefabricated concrete construction produces less waste and timber construction produces more waste than the on-site construction.
The environmental impact analysis for whole building life cycle showed that generally the concrete construction building complex has higher total Global Warming Potential than the timber construction building complex. However, the timber construction has higher Global Warming Potential during the construction stage. The highest Global Warming Potential for concrete construction comes from concrete and for timber construction – from timber as these are the most frequently used construction materials.
This research concluded that the prefabricated timber construction is more sustainable in long term than the prefabricated concrete construction because the construction materials can be easily reused, recycled, and recovered compared to the concrete construction materials.