1. Compliance with NZBC F4 (Safety from Falling)
- Glass: Must use safety glass (tempered or laminated) per AS/NZS 2208 to prevent shattering. Acts as a solid barrier, eliminating gaps.
- Aluminium: Must ensure gaps between vertical/horizontal elements ≤100mm to prevent child entrapment. Requires careful spacing of balusters.
2. Structural Integrity (NZBC B1)
- Glass: Thickness (typically 12–21.5mm) must withstand wind loads (calculated per NZS 3604). Frameless designs need robust fixings.
- Aluminium: Requires engineered profiles to resist deflection (e.g., wind loads in coastal areas). Often paired with stainless steel brackets.
3. Durability (NZBC B2)
- Glass: Resistant to corrosion but prone to scratching. Requires UV-stable interlayers for laminated glass in sunny climates.
- Aluminium: Must be powder-coated or anodized (e.g., Auckland coastal zones require marine-grade coatings).
4. Maintenance
- Glass: Frequent cleaning to avoid watermarks; scratches may require panel replacement.
- Aluminium: Repainting/recoating every 10–15 years; corrosion checks in salty environments.
5. Visibility
- Glass: Unobstructed views, ideal for coastal properties or scenic areas (e.g., Queenstown).
- Aluminium: Partial obstruction due to posts/rails; better for privacy.
6. Environmental Impact
- Glass: High embodied energy (production) but 100% recyclable. Avoids resource depletion if reused.
- Aluminium: Energy-intensive production (≈14 kWh/kg) but highly recyclable (≈75% recycled content in NZ).
7. Fire Safety (NZBC C3)
- Glass: Non-combustible but can shatter under extreme heat unless fire-rated.
- Aluminium: Non-combustible (meets C3.4/3.7 for fire resistance).
8. Weather Resistance
- Glass: Performs well in rain/humidity but may show water spots. Avoid low-quality sealants to prevent leaks.
- Aluminium: Vulnerable to corrosion if coatings fail (critical in Auckland’s marine zones).
9. Installation Complexity
- Glass: Requires precision (e.g., laser-levelling for frameless). Specialist installers needed.
- Aluminium: Modular systems simplify installation; DIY-friendly for basic designs.
10. Cost
- Glass: $400–$1,200 per linear metre (high-end finishes cost more).
- Aluminium: $200–$600 per linear metre (powder-coated vs. anodized).
11. Design Flexibility
- Glass: Limited to flat/curved panels; minimal frames.
- Aluminium: Customisable shapes (e.g., curved, geometric); wide colour range.
12. Acoustic Performance
- Glass: Reduces noise transfer in windy areas (e.g., Wellington).
- Aluminium: No inherent soundproofing; gaps allow noise penetration.
13. Thermal Performance
- Glass: Poor insulator unless double-glazed (rare for balustrades).
- Aluminium: Conducts heat/cold; thermal breaks recommended.
14. Handrail Compliance (NZBC D1/F4)
- Glass: Handrails must be integrated (e.g., clamped channels) and 900–1000mm high.
- Aluminium: Rails often pre-engineered to meet height/grip standards.
15. Load-Bearing Capacity
- Glass: Must withstand 0.5 kPa live load (residential) or 3.0 kPa (commercial).
- Aluminium: Engineered for point loads (e.g., leaning).
16. Compliance Documentation
- Glass: Supplier must provide proof of AS/NZS 2208 compliance.
- Aluminium: Certificates for coating durability (e.g., 25-year warranties).
17. Recyclability
- Glass: Fully recyclable but rarely recycled in NZ due to processing costs.
- Aluminium: Highly recycled; NZ recycles ≈90% of aluminium scrap.
18. Lifespan
- Glass: 20–30 years (if maintained).
- Aluminium: 25–50 years (with proper coatings).
19. Wind Zone Compliance (NZS 3604)
- Glass: Requires thicker panels in high-wind zones (e.g., Cook Strait).
- Aluminium: Additional bracing for exposed sites.
20. Aesthetic Longevity
- Glass: Timeless but shows aging (sealant discolouration).
- Aluminium: Trends affect colour popularity; easier to repaint.
Building Code Focus
- F4: Both systems must prevent falls (gap compliance for aluminium, unbroken barriers for glass).
- B1: Structural calculations for wind/loads mandatory.
- B2: Coatings/glass treatments must meet 15-year durability minimum.
- E2/External Moisture: Sealants must prevent water ingress (critical for aluminium connections).
Environmental Considerations
- Carbon Footprint: Aluminium has higher upfront emissions but better recyclability.
- Local Sourcing: NZ-made aluminium (e.g., NZAS) reduces transport emissions.
- Eco-Certifications: Aluminium with Environmental Choice NZ labels preferred.
Summary
- Choose Glass For coastal views, modern aesthetics, and low maintenance (if budget allows).
- Choose Aluminium For cost-efficiency, recyclability, and design versatility in harsh climates.
Always consult a licensed building professional and check Auckland Council’s Unitary Plan for site-specific rules (e.g., heritage overlays).