A problem with the construction line of business versus the environment is that there are not that much knowledge and rules around the carbon dioxide emissions that several construction projects releases. A lot of companies that we contacted didn´t have the knowledge about the carbon dioxide that releases from the construction projects that they´ve built. This is understandable because it is a very difficult calculation to do, it requires very advanced tools and knowledge around the subject to make detailed calculations. With this master thesis, we want to compare prefabricated buildings with different materials from an environmental perspective with a focus on the carbon dioxide. The different materials we are comparing are steel and tree.   The purpose with this master thesis is to create a basis for Riki AB so that they will have a better sight on the environmental impact from their steel prefabrications which is shipped from China and this will be done with a comparison between a Swedish traditional half prefabricated apartment building.   The first step for the thesis has been a literature study and interviews about the subject. The obtained literature study consists of rapports, relatable thesis, analysis and digital internet sources. The interviews were implemented with companies which were knowledgeable of prefabrication and materials, this was done to get a deeper understanding of the materials effects of the environment.   The result of this examination results that the prefabricated apartment buildings made of steel from China has a larger carbon dioxide emission compared to the Swedish half prefabricated apartment buildings made of tree.