The Green Dip: Covering the City with a Forest

The Green Dip is a multi-year research project by The Why Factory at TU Delft (2018–2024) that asks a fundamental question: what if the 3% of Earth's land surface occupied by cities became urban forest? Led by Prof. Winy Maas with researchers Javier Arpa Fernández, Adrien Ravon, and Lex te Loo, the project developed the Green Maker — a parametric tool cataloguing 4,500 plant species across 14 global biomes, quantifying the environmental impact of radical urban greening across 11 measurable parameters. The research culminated in a 352-page book ( nai010 publishers , 2024, ISBN 978-94-6208-794-1), a 2,340 m² exhibition at the O2 Museum in Hangzhou, and a presentation at Designblok Prague in 2024. The Question Cities occupy approximately 3% of Earth's land surface but generate the majority of global emissions and ecological footprint. Forests cover roughly 30% of land but are shrinking. The Green Dip inverts this condition: what if that 3% became urban forest? What are the real, measurable environmental benefits — and what are the costs, limits, and contradictions? The project refuses to treat green as an aesthetic alibi or marketing gesture. It builds a quantification framework — biome by biome, species by species, building by building — to test whether radical urban greening produces meaningful planetary impact or remains a well-intentioned illusion. This is not a manifesto. It is a measurement instrument. Methodology The research follows a three-part structure that runs through the studios, the book, and the exhibitions — each part building on the previous, scaling from botany to architecture to territory. Part 1 — Green Planet: Biome Classification The world is divided into 14 biomes using the Köppen climate classification. For each biome, native plant species are catalogued with full ecological data: dimensions, soil volume, weight, water consumption, daylight needs, maintenance costs, seasonal growth patterns, and ecosystem services — CO₂ absorption, O₂ production, temperature reduction, water retention, particulate absorption, noise reduction, and biodiversity support. The initial catalogue produced at IAAC Barcelona covered 58 species across all 14 biomes. By the final publication, the database had grown to 4,500 species. Part 2 — Green Buildings: The Green Maker Tool A parametric system combining architectural knowledge with botanical knowledge. Nine greening strategies can be applied to any building typology: green sticking, green perching, green dripping, green lifting, the green hat, green infilling, camouflaging, scooping, and green timber. The tool works in Rhinoceros 3D with Grasshopper, placing grasses, shrubs, and trees on any building surface — roofs, facades, terraces, balconies, walls, floors, interior walls, even furniture. Each intervention is calculated across 11 environmental parameters: albedo, biomass, carbon storage, CO₂ absorption, heat island effect, humidity, NO₂ absorption, O₂ production, temperature, evaporation, and