Exterior living walls are similar in concept to interior ones but built for outdoors. They typically have robust construction, drainage, and choice of hardy plants.
- How it works: These systems attach to building exteriors or freestanding structures. They often use modular panels with soil or hydroponic media, or large troughs/boxes. A complete irrigation system is mandatory (usually with drainage into the ground or a reservoir). Typical systems include a structural backing (drip tray or substrate box), waterproofing, and irrigation at the top feeding down.
- Ideal uses: Building facades (new or retrofits), screening parking structures, covering blank walls, insulating glass buildings, or on fences. Also used on construction hoardings (temporary installation) or inside courtyards. Exterior walls can support taller vegetation and even vines under a trellis.
Pros
- Exterior living walls can significantly affect microclimate.
- By shading walls and through evapotranspiration, they cool surfaces – one study recorded wall surface drops of ~14°C compared to bare wall. This reduces AC demand. They capture rainwater and slow runoff, improving stormwater management.
- Facade plants trap particulates and absorb CO₂, enhancing air quality. They provide habitat and connectivity for wildlife: native wildflowers and grasses on walls can feed bees and insects.
- Aesthetic and branding benefits are high (e.g. covering unsightly elements with gardens).
cons
- These systems are expensive to install and maintain. The plantings face full sun, wind, and cold, so plant mortality can be high if not chosen well.
- Structural concerns are critical: saturated green walls can weigh 50–100 kg/m² (e.g. ~75 kg/m²) plus wind loads.
design & maintenance
- Location: Orientation matters. South or west-facing walls get the most sun, allowing flowering, sun-loving species; north-facing walls require shade-tolerant plants. Wind and exposure must be checked.
- Irrigation: A fully engineered irrigation system is needed. This often includes a pump, filter, and controller in a “plant room” or outdoor cabinet. Overflow drains must be directed safely. In freezing climates, use frost-protected water lines and timers.
- Support Structure: Engage a structural engineer to verify that the wall or frame can bear the load. Anchor points must be compatible with the facade material.
- Plant Selection: Use hardy, low-maintenance perennials, shrubs and grasses suited to the local climate. Incorporate many evergreens for year-round cover; include flowering plants or habitat boxes to support pollinators. Native species are preferred for biodiversity.
- Access: Plan scaffolding or maintenance access from the start. Facades may require rope access, catwalks, or lifts for pruning and repairs.
- Regulations: Check local building codes (e.g. wind load, fire rating of panels) and standards (CWCT, BREEAM, etc.). Green facades can contribute to sustainability credits but may need planning approval.
