From Seeds to Cities: Retrofitting Vegetation into Urban Habitats with Environmentally Computed Architecture

What:
Where:
When:
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Hydroponic Canopy
Oakland example
2022
UC Berkeley M.S. Thesis
Simon Schleicher
Paz Gutierrez
Iryna Dronova
Cody Glen
Mickey Mangan

Our conventional mode of urbanism has manifested severe threats to health of the environment and ourselves. We’ve terraformed biodiverse habitats into urban jungles with an overwhelming abundance of impervious, and often toxic, materials that facilitate heat stress while denying the ecological function on which we depend. The garden city movement reasonably attempted to reunite built and natural realms, however it drove a logistical impracticality and lead to a sprawling export of our civilization’s assault on the environment. In the face of the current multi-faceted environmental crisis, our cities will have to densify in the coming decades so that we can live with a smaller footprint, both spatially and environmentally. With this increased densification though, the problem becomes: how can we welcome the beneficial features of the natural environment (microclimate management, ecosystem services, and beauty) while simultaneously accelerating the practices which expelled them in the first place?

This project proposes a new system of high density cohabitation with nature by drawing inspiration from the smallest scale of a plant (seeds) to the largest scale of construction (cities). Insight is gathered from these disparate scales to inform an architectural intervention that negotiates and reconciles the built and natural dimensions in a radical but sensitive way. This project outlines a universal design solution of a lightweight cablenet intervention that can be strategically retrofitted within dense urban environments to create healthier public spaces. This cablenet is modified to host herbaceous vegetation that will seasonally adapt to provide comfortable space for citizens and an ecological asset for pollinators - an invasive architecture for native plants.

Physical modelling and testing is done as a proof-of-concept while digital simulations help project the designs and discoveries of this thesis into a full-scale urban intervention that attempts to balance many anthropogenic and environmental inputs.

Seed Germination Capsules - Bioprinting

These capsules are intended to help plants grow from seed within their permanent architectural system. A bioprinting workflow was developed in order to prototype a seed germination capsule to help reliably coax seeds out of their fragile embyotic state.

The ink is comprised of 5% sodium alginate and 0.3% activated carbon. The inclusion and amount of activated carbon was based off previous hydrogel research into germination efficiency with a substitute natural hydrogel. Hydrogels are advantageous for maximum retention and steady delivery of moisture for seeds within.

Seed Germination Capsules - Casting

The capsule fabrication method was changed to a casting technique to reduce limitations on volume and production throughput. This required the hydrogel mixture to change from a sodium alginate base to an agarose base. Agarose is a common substrate for performing laboratory germination tests, however, so its effectiveness has already been proven. The same activated carbon ratio was used with an updated design that was shaped to be squeezed open for implanting seeds.

Seed Germination Capsules - Performance

Four head-to-head germination experiments were conducted between the capsules and an off-the-shelf system (peat plugs) under conditions of both controlled and uncontrolled humidity. 3/4 of test results reflected an increased germination viability with the experimental capsules.
These capsules can potentially make off-site greenhouses obsolete for living walls, reducing the embodied energy of a living system and encouraging the use of more ecologically appropriate plant communities.

Scrophularia californica - California Bee Plant

City Suitability Analysis

At the other end of this project’s spectrum, analysis is done at the urban scale to filter for enclaves where an intervention for shade and biodiversity is most needed. For the purposes of this project, Oakland was chosen as a test case. This is accomplished by analyzing data with GIS software to account for high surface temperature, low vegetation occurence, distance from public green space, and pollution vulnerability. These four metrics are weighed and multiplied together to produce a final composite intervention priority map.

This map provides a general idea of where vegetation can provide the most benefit, but the specific intervention proposed by this project requires a more careful visual combing of the urban fabric to identify appropriate enclaves. Using this map, areas of highest concern were analyzed on Google Maps and in person to confirm an appropriate example site.

Normalized Difference Vegetation Index (NDVI)

Distance from Existing Public Green Space

Canopy Form-Finding

Looking closer at an example site, a series of potential interface points are identified on the facades of existing buildings. A multi-objective optimization algorithm is applied to iterate through different combinations of these points for generating a dynamically relaxed cablenet canopy.

Simulation data for yearly Incident Radiation and Average Curvature is collected for each iteration and organized in Thread for closer evaluation. This helps produce a form of the canopy that will intercept more sunlight with plants to increase the photosynthetic/ microclimate management potential, while retaining a reasonable degree of stiffness and security. By this process, the canopy becomes phototropic, emulating the behavior of the plants that it will harbor.

This workflow allows for decisions that are informed by data and not purely driven by it in a deterministic way, which is important in projects with other potential contingencies, such as the contextual interfacing features of buildings or design preferences of stakeholders.

The chosen cablenet iteration is put through a final simulation for the average daily hours of direct sunlight that hit each face of the mesh. These faces are binned into three categories that approximately correspond to different plant sunlight preferences:

Full shade
Part shade
Full sun

daily average direct sunlight hour simulation

Vegetation Programming

A plant pallette is derived from a spreadsheet of herbaceous plants native to the site, listed in order of their pollinator attraction (Calscape.org). Grasshopper reads this external Excel spreadsheet and feeds it into a custom python component that extracts and organizes the plants into the three sunlight bins (full shade, part shade, full sun).

The custom grasshopper component then maps this list of plants and their associated 3D models to each cell of the cablenet canopy based on the plants’ sunlight preferences. This is balanced with user-defined preferences for three additional variables:

biodiversity
distribution limit
seasonal balance

Biodiversity - increasing number of species selected for distribution

Limit - increasing limit of species occurrence before next plant

The seasonal balance logic is implemented to help distribute blooms of the whole canopy system across the entire year to ensure that pollinators are always being served. The following graph shows the standard deviation of blooms across the seasons as the seasonal balance check increases in frequency.

Seasonal Balance - Increase frequency of seasonal bloom balance check

Modular Interface Design

Devising the material interface for the plants is one of the highest priorities for this project. The mesh itself would be composed of a 3mm stainless steel cable net with nodes clasping together alternating cables to create 60^o angles when tensioned into position. This formation allows for an efficient and repeating circle packing where each circular module can be linked to six of its neighbors. Not only does this create a more continuous irrigation network, but it also prevents the modules from swivelling on the connecting cable net nodes. Irrigation can be locally controlled with different flow rate emitters.

The modules would be composed from a circular hoop which secures a series of textiles. at the base are textiles for waterproofing, capillary distribution, and substrate. The upper textile is a net which provides shade for vulnerable seedlings plants, but it remains porous for plants to grow through. These upper and lower textiles are spaced apart by a central mast which can be angled to account for the vertical and lateral declinations associated with any given position across the cable net, ensuring that a cone shape is created for funneling irrigation toward the center where the plant is rooted. This mast also provides a drainage vector for runoff that would otherwise pool, preventing extra weight and root rot.

The irrigation system is designed to flow from high connection points and branch into clusters of modules to create a continuous irrigation system without too much pressure that also helps reinforce the stability of the modules. The discharge network is programmed to connect each module to the closest neighbor that’s furthest downslope. Once water makes its way to the lower urban interface points, it can be channelled into basins that pump water back to the high points, creating a recirculating system.

Space between the modules would become filled with foliating vegetation in the warmer months and open back up in the colder ones as the pants go through their seasonal cycles. By leveraging plants with this behavior, the system passively adapts to keep the shade proportional to the heat, an ideal material for managing the microclimates of pedestrian realms of our cities.

Prototype Installation

A working prototype was installed with three different herbacious native perennials in a recirculating hydroponic system. This installation is temporary but the modules will be reconfigured on a different site for longer-term evaluation of their performance in sustaining plants.

ERIC FUTERFAS