Green Infrastructure: Living Walls and Rooftop Gardens
Introduction to Green Infrastructure
Influential Figures in Green Architecture:
Friedensreich Hundertwasser (1928 - 2000): An Austrian artist and architect known for his ecologically-minded designs.
Patrick Blanc (1953 - \text{present}): A French botanist who coined the term "mur vegetal" (green wall).
Historically Common Climbing Plants:
English ivy (Hedera helix), an evergreen species.
Boston ivy (Parthenocissus tricuspidata).
Lecture Learning Outcomes:
To understand the importance, benefits, and design considerations of green infrastructure (specifically living walls and rooftop gardens).
To grasp the technical design principles for green infrastructure (living walls and rooftop gardens).
Defining Green Infrastructure
Comprehensive Definition (Dover, 2015): "Green infrastructure is the sum of an area’s environmental assets, including stand-alone elements and strategically planned and delivered networks of high-quality green spaces and other environmental features including surfaces such as pavements, car parks, driveways, roads, and buildings (exterior and interior) that incorporate biodiversity and promote ecosystem services."
Core Principles Green Infrastructure Promotes:
Smart growth.
Smart conservation strategies.
Land and water conservation.
Mapping of natural systems (e.g., ridges, streams, wetlands).
Provision of ecosystem services.
Key Characteristics of Green Infrastructure:
Serves as a strategic framework for planning conservation and development.
Represents a long-term commitment.
Requires collaborative effort from all community sectors, including private landowners.
Dictates smart development and land use practices.
Integrates infrastructure with ecological goals.
Provides vital ecosystem services.
Forms an integrated network of hubs, links, and sites.
Acts as a natural solution for addressing drainage, heat, air, and water quality issues commonly found on commercial properties.
Ecosystem Services Provided by Green Infrastructure
Green roofs and walls provide various ecosystem services, categorized as:
1. Provisioning Services:
Food: Facilitates food gardens.
Medicine: Supports traditional medicine cultivation.
2. Cultural Services:
Aesthetic: Enhances the aesthetic appeal and cultural value of communities.
Spiritual: Creates spaces conducive to contemplation and prayer.
Recreation: Provides areas for recreational activities.
3. Regulating Services:
Regulates climatic conditions, contributing to the reduction of the Urban Heat Island Effect (UHIE).
4. Supporting Services:
Provides essential habitats for a diverse range of species.
Example Plant Species (with notes):
Portulacaria afra.
Senecio tamoides.
Cussonia sp. (Caution: known for invasive roots).
Green Roofs
Benefits of Implementing a Green Roof:
Offers significant aesthetic value.
Functions as an effective rainwater buffer.
Purifies ambient air.
Reduces urban ambient temperatures, mitigating the Urban Heat Island Effect (UHIE).
Increases biodiversity within urban environments.
Creates habitat for urban wildlife.
Enhances a building's amenity and marketing value.
Provides social value and event space.
Regulates indoor temperature by acting as an insulator for the building.
FWEC-Related Benefits (Based on a Johannesburg study, example values):
Local Food Production: Yields food with associated carbon savings (e.g., +8.66 kg CO2e for carbon and +6.83 kg of food from system 'a'; +\text{variable} kg of food, +2.71 kg CO2e for carbon from system 'b').
Direct Energy Saving: From +36.16 MJ (AEe) to +103.62 MJ.
Direct Water Saving: Ranging from +95.62 L to +2159.18 L or +1159.97 L.
Direct Carbon Capture: Approx. +0.37 kg CO2e to +4.46 kg CO2e.
Life Cycle Energy Consumption: Varies, e.g., +97.18 MJ (AEf) to +45.40 MJ, +130.97 MJ.
Avoided Transboundary Energy Footprints (AEf, AWe, AWW): Examples include -88.59 MJ, -89.32 MJ, +22.48 MJ.
Life Cycle Water Consumption: Reported as +1155.77 L.
Avoided Transboundary Water Footprints (AW, AWe, AWW): Examples include -9.44 L, -186.28 L, +36.22 kg (likely an error, should be L).
Life Cycle Carbon Emissions: Totaling +310.85 kg (likely CO_2e).
Avoided Transboundary Carbon Footprints (ACf, AC, Acw): Examples include -5.55 kg CO2e, +5.57 kg CO2e, +0.12 kg CO_2e.
Extensive vs. Intensive Green Roof Systems:
Comparison Table:
| Parameter | Extensive | Intensive |
|---|---|---|
| Grain size | Coarse | Fine |
| Water retention | Low | High |
| Air volume | High | Low |
| Nutrient reserves | Low | High |
Extensive Green Roof Systems:
Covers a large area.
Can be installed on roofs with low load-bearing capacity.
Offers thermal benefits.
Relatively inexpensive.
Limited plant palette, primarily mosses, herbs, succulents, and grasses.
Requires low maintenance.
Modular systems are often utilized.
Characterized by a thin soil layer (60-200 mm).
Requires little to no irrigation.
Offers limited access and program opportunities.
Intensive Green Roof Systems:
Offers high aesthetic value.
Provides significant water and thermal benefits.
Relatively expensive.
Allows for a large variety of planting, including ground covers, shrubs, and trees.
Maintenance intensive.
Features a greater depth of growing medium (150-600 mm).
Heavy due to soil volume and water saturation, necessitating a high load-bearing roof structure.
Requires regular irrigation.
Designed for public access (direct contact) and a broad range of programs.
Key Design Considerations for Green Roofs:
1. Depth (of Growing Medium):
For Trees: 800-1300 mm.
For Shrubs: 500-600 mm.
For Groundcovers: 300-450 mm.
For Lawn/Vedgrass: 150-300 mm.
2. Weight: Must account for the saturated weight of the growing medium and plants.
3. Waterproofing: Critical to prevent water ingress into the building structure.
4. Protection: Layers to shield the waterproofing membrane from damage.
5. Irrigation:
Requires sleeves/water points integrated into planters.
A controller for automated watering.
A reliable water connection.
An appropriate system (e.g., drip, mist, spray) tailored to plant needs.
6. Drainage:
Full Bore Drain: Typically 50-150 mm diameter, must be drilled by the main contractor in the slab, with positions specified to the engineer in advance.
Fall: A screed with an approximate slope of 1:40.
Inspection Hole: Covering the full bore with concrete/polyethylene pipe and geotextile for maintenance.
Typical Green Roof Layers (from bottom up):
Structural slab.
Screed to fall (minimum 1:80 slope, minimum thickness 45mm as per Derbigum spec, or 30mm if 13MPa strength is achieved and approved).
Bitumen prime substrate.
Derbigum CG3mm Torch-on waterproofing.
Derbigum CG4mm H Torch-on horticultural waterproofing membrane (with Preventol to inhibit root growth into laps).
Integrated drainage and protection sheet (e.g., Delta-Floraxx Top or Delta-Terraxx for intensive systems).
Filter layer (geotextile, 2-3 layers).
Drainage layer (gravel/coarse sand or flow net/dimple drain).
Moisture retaining layer (optional).
Growing medium/soil (specified by landscape architect).
Plants/grass cover (specified by landscape architect).
Waterproofing Specifics (Derbigum and Testing):
Derbigum® Civils Grade 3mm & CG4mm H (Horticultural) Torch-On:
Extensive gardens: Used with Delta-Floraxx Top drainage membrane.
Intensive gardens: Used with Delta-Terraxx 9mm high-density polyethylene dimpled drainage and protection sheet.
Applied in layers with 100mm side and 150mm endlaps, torch-fused and installed by approved contractors with a ten-year guarantee.
Derbigum CG: Considered the best choice for specifications where the area will be buried beneath other building elements.
Derbigum SP Dual Reinforced Membrane: Specified for exposed waterproofing.
Flood Testing: Essential to ensure waterproofing integrity; involves flooding the tested area with potable water to a minimum depth of 25 mm and a maximum depth of 100 mm.
Green Walls
Comparison of Three Vegetated Wall Methods (Sheweka & Magdy, 2011):
1. Climbing Plants (Green Facades):
Wall Plants: Climbing plants.
Growing Media: Soil on the ground or in planter boxes.
Construction Type: Minimal supporting structure needed.
2. Hanging Down Systems:
Wall Plants: Plants with long, hanging-down stems.
Growing Media: Soil in planter boxes at every storey.
Construction Type: Planter boxes and supporting structures built at each storey.
3. Module Systems (Living Walls):
Wall Plants: Short plants.
Growing Media: Lightweight panels of growing media (e.g., compressed peat moss).
Construction Type: Supporting structure for hanging or placing modules built on façades.
Green Facades:
Feature climbing plants rooted in the ground.
Supported by a trellis-like structure often attached directly to the building façade.
Typical climbers include Hedera helix, Parthenocissus tricuspidata, and P. quinquefolia.
Direct Green Facade: Plants grow directly onto the wall surface or minimal support.
Indirect Green Facade: Plants grow on a separate, spaced-off support structure, creating an air gap.
Living Walls (Vertical Gardens/Mur Vegetal):
Self-sufficient systems completely covered by plants.
Can be free-standing or an integral part of a building.
Plants receive water and nutrients from a dedicated root medium (soil) or through hydroponics technology.
Modular Living Wall Systems (LWS):
Involve growing plants in an irrigated growing medium contained within specific modules.
Require structures of specific dimensions to support these elements, or elements fixed directly to the vertical surface.
Currently the most widely used systems in South Africa.
Popularity stems from the instant visual impact upon installation, as plants can be pre-grown off-site.
Individual plants can be easily replaced with minimal aesthetic or surrounding plant disturbance due to separate modules.
Can be imported or locally produced.
Classifications of Modular LWS:
Trays: Containers or modules attached via an interlocking system, each holding an individual plant and growing media. Typically made of lightweight polymeric material, mounted on a frame, and linked by irrigation.
Planter Tiles: Tiles with pockets for individual plants, featuring flat back edges that are glued or mechanically fixed to the vertical surface. These function as modular cladding.
Flexible Bags: Made from flexible polymeric material, filled with growing media, suitable for irregular surfaces like curved or sloped walls.
Advantages of Modular LWS:
Instant Effect: Achieved upon installation due to pre-grown plants.
Maximum Aesthetic Effect: Maintained through easy removal and replacement of individual plants.
Resilience: Generally more resilient than continuous systems.
Weaknesses of Modular LWS:
Plant Resilience and Durability: Concerns about long-term plant health.
Sustainability: Questions regarding the system's sustainability throughout its life-cycle.
Ecological Footprint: Impact of materials used for supporting structures and elements.
Resource Requirements: High water and maintenance needs.
Financial Feasibility: Can be expensive; imported systems average R7000/m^2, while local systems are around R1500/m^2.
Eco Green Wall (Addressing Weaknesses):
Aims to enhance sustainability, system resilience, maintenance, and economic feasibility.
Constructed from lightweight blocks made of a locally developed recycled polystyrene aggregate and cement mixture.
Results in a lightweight, fire-resistant system with acoustic and thermal benefits.
Limited exposure of the growth medium within the blocks promotes moisture retention and plant durability.
**Other Advanced Green Wall Systems:
Hydroponic Wall Systems:
Utilize lightweight screens where plants grow without a substrate.
Depend entirely on a permanent supply of water and dissolved nutrients (Manso & Castro-Gomes, 2014).
Aquaponic Wall Systems:
Combine vegetable production with fish farming.
Fish waste serves as the primary nutrient source for the plants.
Substrate-free, relying on continuous water and nutrient supply.
A delicate and complex system.
Aeroponic Wall Systems:
A soil-less system where a nutrient-rich solution is misted directly onto plant roots.
Initially explored in the Netherlands, introduced in South Africa by Impilo.
Features lightweight screens.
Plants are entirely dependent on a continuous provision of nutrient-enriched mist.
Key advantage is high yields.
Specific Green Wall Implementations and Plant Types (from Plant Sciences, UP; KWP architects and landscape architects):
Dry Wall (North-facing): Experiences 2X radiation; suitable for cremnophytic plant species.
Wet Wall (West-facing): Experiences \frac{1}{2} radiation; suitable for hydrophilic cremnophyte plant species.
Design Examples: Includes structures with planter boxes supported on steel frames, 200mm rock-filled galvanized steel mesh baskets, steel catwalks for access, often incorporating Kirkia acuminata and aquatic plants. Other designs feature 800mm cavity/workspace for non-pendent cremnophytes (Senecio spp.) or 100mm diameter PVC pipes filled with soil for pendent cremnophytes (Aloe hardyi).
Applications of Green Walls:
Schools, hospitals, hotels, restaurants, retail stores.
Residences, public and private sector office buildings.
Green Wall Design Checklist:
Light/aspect (sun exposure).
Type of system (e.g., modular, hydroponic).
Drainage point location.
Availability of water and electrical points.
Waterproofing of the underlying structure.
Weight considerations (especially for façade-mounted systems).
Appropriate plant species selection.
Growing medium characteristics.
Irrigation requirements (e.g., typical usage of 3 to 5 L/m$^2$/day).
Budget constraints.
Maintenance plan.
Accessibility for installation and maintenance.