The aim of this Master Thesis is to investigate and quantify the climate impact for two floor system alternatives for the Cederhusen project, that is the 8 floors timber-based buildings located at Sankt Eriksplan in Stockholm. The overall motivation for this study is the fact that the construction industry is a major contributor to the total amount of the global greenhouse gas emissions. Therefore, in order to reduce these emissions new solutions, practices and applications must be adopted. An environmental attentive choice of materials used in structures has the potential of reducing the emissions. The first alternative is the existing floor system solution used by Folkhem. The second is a new type of floor system solution patented by Granab. Each floor system contains two segments: a structural part and a sub-floor part. The structural part in both alternatives contain an adding weight component to improve the dynamic performance of the relatively light weight high-rise timber buidlings. Both floor systems are thus so-called hybrid systems, where Folkhem's solution combines cross-laminated timber (CLT) and steel fiber reinforced concrete, and Granab's solution combines CLT and gravel. The specific objective was to compare the emission of greenhouse gases related to each floor system and their components by a so-called comparative life cycle assessment (LCA) methodology using a well-defined functional unit. The functional unit must consider all significant performance requirements obtained by the floor system, including load bearing capacity, dynamic performance, sound proofing, fire safety, surface flooring and maximum acceptable building height. The method of determining the climate impact is based on the “Anavitor Concept”, an innovative and digital approach to LCA calculations, to quantify and compare the environmental impact of the two floor systems through their lifetime, aiming for the user to not be an LCA expert, but to be the one who develops the design solutions, called “End-User”. Therefore, this concept performs direct LCA calculations from the BIM model by allowing access to environmental database, which contains life cycle analysis data approved and provided by LCA environmental specialists, and conveniently link material component against an industry-wide resource register receipt, called “Cross-Referencing”. The results show a significant decrease of climate impact with 33 % CO2e/m2 for the Granab’s alternative floor system compared to the existing floor system designed by Folkhem. Moreover, a direct comparison of the climate impact of Folkhem´s versus Granab´s adding weight system itself, shows a remarkable decrease of climate impact with 65 % CO2e/m2 emissions reduction for the Granab system.  Thera are several reasons for these remarkably results, however, the building material selection of gravel over concrete has the greatest influence. In practice, the ability to avoid the environmental impact of cement’s manufacture process in the production stage, A1-A3, is identified as the hot spot of this study. In addition, the environmental impact results signify the importance of a wise selection of the manufacturer and their factory location, mainly by selecting a factory located as close as possible. However, in practice, there are also other factors which need to be considered when choosing a supplier. Moreover, allowing the user to not be an LCA expert but to be the one who develops the design solutions, based on the “End-User” idea in the “Anavitor Concept” applied in this study, has novel benefits. By implementing LCA analysis during the architectural and structural design process, additional quantified environmental results can be instantly considered as additional causal numerical factors in the design process and directly affect executive decisions in earlier design stages for environmental matter as well. “Anavitor Concept” is a game changer regarding LCA in the construction sector. A future where every consulting building company around the globe would have access to open verified regulated environmental database and simply with their BIM model would be able to receive immediate quantified and verified environmental impact outputs in the early stages of design by the designers themselves and not LCA expert consultant, is an environmental dream come true. The “Anavitor Concept” should be adopted and expend outside the Swedish market and the environmental database should be adapted and modified to each national construction market around the globe.