Currently set climate targets regarding carbon dioxide emissions mean that emissions from the construction industry must be reduced. One option for reducing the carbon footprint of a building's foundation could be to completely replace the concrete slab with a CLT foundation slab. The aim of the report is therefore to investigate how a CLT slab can be designed and then determine whether it has a smaller carbon footprint than a conventional reinforced concrete slab.  For the study, an example house was designed to generate loads, for which the CLT slab and concrete slab were then designed. The CLT slab was designed using FEM design software. The concrete slab was designed using hand calculations according to Eurocode 2. The material quantities from the respective designs were applied in an environmental calculation tool where the climate impact from the manufacturing phase was calculated. The result showed a 61 - 68% lower environmental impact in the form of carbon dioxide equivalents from the CLT foundation compared to the concrete foundation. However, the results of the climate analysis do not show with certainty that a CLT slab has a lower climate impact than a concrete slab, even though it has a lower climate impact during the manufacturing process. One factor that affects the result is the lifespan of the materials in the different foundation constructions, which can differ by as much as 50 years. Further research in construction solutions for CLT foundation slabs, long-term moisture protection and lifetime climate analysis is required to obtain a more distinct result in this study.