Intensive Green Roof
Key Benefits
- Water Management: Very High Runoff Volume Reduction; High Peak Flow Attenuation; Enhanced Water Quality Improvement. (C753 S12.4, S12.5)
- Building Performance: Enhanced Thermal Insulation; Increased roof lifespan; High Noise Reduction/acoustic insulation (46 db). (GI Guide)
- Environmental: Enhanced Urban Cooling; Enhanced Air Quality Improvement; Higher Carbon Sequestration/Storage potential. (C753 Ch 5; GI Guide)
- Biodiversity: Creates diverse habitats (meadow, shrub, woodland edge analogue); Supports wider range of species; Contributes significantly to ecological networks. (C753 S12.7; GI Guide)
- Amenity: Creates accessible recreational/amenity space (roof garden/park); High aesthetic value. (C753 S12.6)
- Metrics: Energy Saving (Below): 6.7% (or better); Surface Temperature Reduction: 14.5°C; Air Temperature Reduction (Above): 1.1°C; Property Value Uplift (Accessible): 6.9%; (Carbon sequestration/storage and water quality benefits likely higher than extensive roofs)
Technical Guidance
Structural Assessment (C753 S12.2)
EVEN MORE CRITICAL. Intensive systems impose very high saturated loads (180-500+ kg/m², potentially >>1000 kg/m² with trees/deep substrate/water features). Detailed structural engineering assessment and specific design/strengthening of the roof structure are essential. Load calculations must account for all components (substrate, vegetation - mature weight, paving, water features, furniture, soil water retention), plus snow and live loads (occupants, maintenance).
Waterproofing & Root Barrier (C753 S12.8)
Requirements are stricter than extensive roofs. Use high-performance, robust, root-resistant waterproofing membranes (FLL certified) or standard membrane plus separate heavy-duty root barrier (e.g., HDPE >0.8mm). Meticulous detailing, protection during installation, and integrity testing (flood test) strongly recommended before overlaying.
Drainage & Irrigation (C753 S12.8.3)
High-capacity drainage layer (e.g., deeper drainage/reservoir boards, aggregate layers) essential. Automated irrigation system (drip, sprinklers) nearly always required for diverse planting in UK climate. Requires reliable water supply, adequate pressure, filtration, control unit, potential fertigation and frost protection. Design for efficient water use. Ensure robust, accessible outlets/inspection chambers.
Growing Medium/Substrate (C753 S12.9; GI Guide - Soils)
Deeper engineered intensive substrate (150mm to >1m). Careful specification needed (meet FLL/GRO Code) balancing water retention, aeration, drainage, stability, nutrient content, and weight minimisation. Use different depths/types for different planting zones (e.g., deeper under trees/shrubs).
Vegetation (C753 S12.10; GI Guide - Planting)
Wide planting palette: lawns (requires maintenance/irrigation), perennials, grasses, shrubs, small trees (subject to structural/substrate constraints). Select species suitable for roof conditions (exposure, depth), desired aesthetic, maintenance level, and biodiversity goals. Use UK natives where appropriate.
Hard Landscaping & Features (C753 S12.6)
Integrate paving, seating, planters, lighting, water features etc., carefully considering load implications, drainage, waterproofing interfaces, material durability, and accessibility compliance (Building Regs Part M).
Edge Detail & Safety (C753 S12.2, S12.8.1; GI Guide)
Robust edge protection (parapets, railings meeting BS 6180) essential for accessible roofs. Vegetation-free margins still required for fire safety and drainage. Consider wind loading on structures/tall planting.
Maintenance (C753 S12.12)
Significantly higher than extensive roofs, akin to ground-level gardens/parks. Requires regular mowing, weeding, pruning, irrigation checks/adjustment, feeding, pest/disease control, structural checks, outlet clearing. Specialist horticultural knowledge often needed.