Green Roof on Span+ | Metal Roof Garden Implementation

Solution

Span+^© Rafter-Mount Platform Configuration‍

System: Span+^© ultra-lightweight rafter-mount platform (12 kg/m²)‍

Rafter spans: 8-12m between support points

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Project Overview

Client: Commercial Office Building (Queensland)
Application: Intensive green roof garden and recreational space
System: Span+^© Rafter-Mount Green Roof Platform
Area: 600m² landscaped rooftop garden
Completion: 14 weeks from design to landscaping

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Challenge Statement

A modern commercial office building with expansive metal deck roofing sought to transform its underutilised rooftop into a premium garden sanctuary for tenants and visitors. The project aimed to create peaceful green spaces, reduce urban heat island effects, and achieve building sustainability ratings while working within the existing metal roof structure's load limitations.

The existing metal deck roof had rafters spaced at wide intervals (8-12m spans) with purlins insufficient to support intensive green roof loads typically requiring 4-6kPa for soil depth, established plantings, and hardscape features.

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Traditional approaches would have demanded

• Structural steel reinforcement framework: $700,000 cost
• 20-week construction timeline
• Complete roof replacement disrupting building operations
• Revenue losses exceeding $200,000 from tenant displacement

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Con-form Group's Technical Solution

Span+^© Rafter-Mount Platform Configuration

• System: Span+^© ultra-lightweight rafter-mount platform (12 kg/m²)
• Rafter spans: 8-12m between support points
• Load distribution: Direct to structural rafters via certified connections
• Height adjustment: 300-600mm variable for drainage gradients

Integrated Landscape Systems

1. Primary deck: Ultra-light gauge steel mesh supporting growing medium
2. Rafter connections: Engineer-certified mounting brackets
3. Root barrier: HDPE membrane protecting metal roof structure
4. Drainage system: Integrated channels directing water to roof outlets
5. Access pathways: 600mm wide maintenance walkways spanning rafters

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Load Distribution Analysis

Rafter Load Management

Traditional approach: Concentrated loads requiring intermediate supports
Span+^© solution: Direct load transfer to existing rafter structure

Spanning capability:

• Traditional systems: 4-6m maximum spans
• Span+^© platform: 12m+ spans between rafters
• Structural efficiency: 83% weight reduction versus structural steel

Advanced Load Distribution

• Span+^© platform: Capable of 2.5kPa, 5.0kPa and greater loads
• Rafter load transfer: Engineered connection points
• Wind load certified: Regions A, B and C compliance
• Critical for metal roof integrity during extreme weather

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Installation Process

Timeline Comparison

Traditional structural reinforcement: 20 weeks
‍Span+^© implementation: 14 weeks

• Engineering/rafter analysis: 3 weeks
• Platform fabrication: 3 weeks
• Installation: 3 weeks
• Waterproofing integration: 2 weeks
• Landscaping: 3 weeks

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Installation Advantages

• Direct rafter mounting eliminates intermediate supports
• No penetration of metal roof membrane required
• Prefabricated sections craned into position
• Weekend installation with zero tenant disruption
• No hot works permits required on metal deck

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Landscape Design Integration

Garden Infrastructure

• Planted areas: 45 landscape zones across rafter spans
• Soil depth: 300-450mm variable for trees, shrubs, and groundcover
• Tree plantings: 12 native species with rafter-aligned root support
• Water management: Integrated drainage to existing roof outlets
• Seating areas: 3 contemplation zones positioned over rafter points

Recreational Features

• Spanning walkways: 300m of elevated garden trails
• Outdoor meeting spaces: 2 covered pavilions using rafter structure
• Recreation zones: Central lawn area spanning between rafter supports
• Educational gardens: Native plant demonstration zone

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Environmental Performance

Temperature Reduction

• Metal roof surface cooling: 65°C → 25°C (extreme summer reduction)
• Building temperature: 4°C average reduction below metal deck
• HVAC load decrease: 28% annual energy saving
• Elimination of metal roof thermal cycling stress

Stormwater Management

• Rainfall retention: 85% of annual precipitation
• Peak flow reduction: 90% during storm events
• Metal roof protection: Reduced thermal expansion/contraction
• Extended roof membrane life: 40% increase in service life

Biodiversity Outcomes

• Native plant species: 25 varieties adapted to elevated conditions
• Wind-resistant plantings: Selected for metal roof environment
• Bird habitat creation: Elevated nesting opportunities
• Urban heat island mitigation across commercial precinct

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Financial Analysis

Capital Cost Comparison

Span+© rafter-mount system: $42,000
Installation & integration: $24,000
Landscaping & drainage: $31,000
Total Span+© solution: $97,000

Traditional reinforcement alternative: $700,000
Cost saving: $603,000 (86% reduction)

Operational Returns

• Property value increase: 18% building valuation uplift
• HVAC energy savings: $14,500/year (higher due to metal roof cooling)
• Roof membrane protection: $6,200/year maintenance savings
• Tenant retention premium: $50,000/year
• ROI period: 1.4 years

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Compliance & Certification

Standards Met

• AS/NZS1170, AS1170.2, AS1170.4: Wind and structural loads
• AS1657: Fixed platforms & walkways
• AS1664.1: Metal roof integration requirements
• Building Code of Australia compliance
• Metal roof manufacturer warranty preservation

Wind Load Certification

• Wind regions A, B and C certified
• Metal roof uplift resistance maintained
• Rafter connection engineering certified
• Extreme weather performance validated

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Project Outcomes

Technical Success

✓ No intermediate rafter supports required
✓ 12m+ spans achieved with existing structure
✓ Metal roof thermal performance improved 28%
✓ 6-week faster delivery than steel reinforcement

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Stakeholder Benefits

• Building owner: $603,000 cost saving, 18% property value increase
• Tenants: Superior thermal comfort, reduced metal roof noise
• Maintenance: 40% extended roof membrane life
• Environment: 13 tonnes CO₂/year sequestration from cooling

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Key Design Innovations

Rafter Integration Optimisations

1. Spanning capability: Eliminated need for intermediate supports
2. Direct mounting: Utilised existing structural capacity efficiently
3. Thermal isolation: Protected metal deck from extreme temperatures
4. Load distribution: Engineered connections optimised for rafter spacing

Metal Roof Applications

• Suitable for 90% of commercial metal deck buildings
• Compatible with standing seam, corrugated, and composite panels
• Preserves roof warranties through non-penetrating connections
• Adaptable to various rafter spacings from 4-15m

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Conclusion

The Span+© Green Roof system transformed an impossible metal roof garden project into a premium landscape amenity through:

Spanning Innovation: 12m+ rafter spans without intermediate supports
Weight Efficiency: 83% lighter than structural steel alternatives
Cost Savings: $603,000 (86%) versus traditional reinforcement
Thermal Performance: 28% HVAC savings from metal roof cooling
Roof Protection: 40% extended membrane life through thermal isolation

This project demonstrates that wide-span metal roofs are ideal candidates for intensive green roof installations. The Span+© system's ultra-lightweight design and rafter-mounting capability opens previously impossible opportunities for rooftop gardens on commercial metal deck buildings.

Critical Success Factor: The 12 kg/m² platform weight, combined with direct rafter load transfer, utilised existing structural capacity while supporting intensive 300mm green roof systems across spans exceeding 12 metres without intermediate supports.

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Technical Specifications

Platform System: Span+© rafter-mount with certified connection brackets
Load Rating: 2.5kPa, 5.0kPa and greater capacity
Spanning Capability: 12 metres+ between rafter supports
Materials: Australian-made ZINCALUME G550 light gauge steel
Warranty: 25-year structural warranty
Wind Rating: Certified for wind regions A, B and C
Standards: AS/NZS1170, AS1170.2, AS1170.4, AS1657 compliance

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Building

Commercial Office Building (Queensland)