In the light of climate change and environmental challenges such as a nitrogen crisis, a decreasing biodiversity and waterlogging, the Dutch government is trying to build 900 000 homes by 2030 while aiming for a reduction of 55% of CO2 in the construction industry. Biobased topping-up of existing tenement flats is proposed as a solution to tackle several issues. A literature review revealed that a top-up structure has the ability to limit the Global Warming Potential (GWP) of housing. From a set of seven biobased resources, wood, hemp, flax, straw, miscanthus, cattail and seaweed, it was concluded that the current Dutch stock is not sufficient to construct all 100 000 required top-ups with locally sourced biobased materials. Scaling up to a sufficient amount of resources by 2030 requires the right allocation of material over the Dutch landscape, and for the region of Zuid-Holland the right allocation over a peat region, a clay region and a sand region. This is necessary because this cultivation can help break the nitrogen impasse and boost the biodiversity. Furthermore, most resources do not compete with food production. A design for a top-up could be constructed with materials that were sourced within 50km reach. The comparison of GWPs of different variations on the design for the top-up showed that the variations with biobased insulation do not always perform better as an additional layer of fire-proofing had to be added to the construction. Biobased materials do however have the capacity to store biogenic carbon which should be taken into account. Knowing this, the Dutch government and the province of Zuid-Holland should try to construct as many top-ups with locally sourced biobased materials as possible, since it is the quickest way to Paris-proof housing.