Why Your Deck's Foundation Matters More Than You Think
The decking boards you walk on get all the attention—but the subframe joists beneath them are what really determine your deck's longevity, safety, and performance.
Traditional timber joists rot from the inside out. By the time you notice spongy boards or creaking underfoot, the damage is done—and you're facing costly structural repairs or complete replacement.
Recycled plastic decking joists solve this problem permanently. Made from 100% recycled plastic, they provide a strong, long-lasting, and maintenance-free foundation for decking and all outdoor structures.
In this guide, we'll cover everything you need to know about recycled plastic joists—from technical specifications and load-bearing capacity to installation best practices and cost analysis.
What Are Recycled Plastic Decking Joists?
Material Composition
Recycled plastic joists are manufactured from:
- Post-consumer plastic waste (e.g., bottles, containers, packaging)
- Post-industrial plastic waste (e.g., factory offcuts, rejected products)
- 100% recycled content—no virgin plastic used
The plastic is cleaned, shredded, melted, and extruded into solid or hollow profiles designed specifically for structural load-bearing applications.
Available Profiles
- Solid rectangular joists: 70mm × 47mm, 100mm × 50mm (similar to timber C16 dimensions)
- Hollow box sections: Lightweight but strong, ideal for spanning longer distances
- Custom extrusions: Available for specialized projects (contact us for details)
Color Options
- Brown (matches timber decking aesthetics)
- Grey (modern, contemporary look)
- Black (commercial-grade, low-visibility subframe)
Key Benefits of Recycled Plastic Joists
1. Never Rots, Warps, or Splits
Unlike timber, recycled plastic is:
- 100% waterproof—no moisture absorption, even in permanent ground contact
- Rot-proof—no fungal decay, even in damp soil or underwater applications
- Dimensionally stable—no warping, twisting, cupping, or splitting over time
Result: Your deck's subframe remains structurally sound for 50+ years.
2. Zero Maintenance
- No painting, staining, or sealing required
- No annual inspections for rot or structural integrity
- No replacement costs for decayed joists
Result: Thousands of pounds saved over the deck's lifetime.
3. High Load-Bearing Capacity
Recycled plastic joists are engineered for structural applications:
- Tensile strength: 15 MPa (ISO 527-2) — comparable to softwood
- Flexural modulus: 1225 MPa (ISO 178) — more flexible under load than timber
- Impact resistance: 14 KJ/m² (ISO 179) — absorbs impacts that would crack timber
- Consistent performance: Maintains full strength for 50+ years (timber loses 50-70% strength as it rots)
Result: Safe, reliable support for heavy foot traffic, furniture, and hot tubs.
4. UV & Weather Resistant
- UV inhibitors molded into the material prevent fading and degradation
- Freeze-thaw resistant—no cracking or brittleness in UK winters
- Salt-resistant—ideal for coastal installations
Result: Performs flawlessly in all UK weather conditions.
5. Eco-Friendly & Sustainable
- Diverts plastic waste from landfills and oceans
- No deforestation—eliminates demand for timber logging
- Fully recyclable at end-of-life (true circular economy material)
- 70% lower energy to produce than virgin plastic
Result: Supports the circular economy and reduces your project's carbon footprint.
Technical Specifications
Solid Joist (70mm × 47mm)
| Property | Value | | ---------------------------- | ---------------------------- | | Dimensions | 70mm width × 47mm height | | Weight | ~5.5 kg/m | | Tensile strength | 15 MPa (ISO 527-2) | | Tensile modulus | 1445 MPa (ISO 527-2) | | Flexural strength | 30 MPa (ISO 178) | | Flexural modulus | 1225 MPa (ISO 178) | | Impact resistance | 14 KJ/m² (ISO 179) | | Max span (400mm centers) | 600mm | | Max span (600mm centers) | 450mm | | Fire rating | Class E (self-extinguishing) | | Temperature range | -20°C to +50°C (operational) |
Hollow Box Joist (100mm × 50mm)
| Property | Value | | ---------------------------- | ---------------------------------------------- | | Dimensions | 100mm width × 50mm height × 5mm wall thickness | | Weight | ~3.8 kg/m | | Tensile strength | 15 MPa (ISO 527-2) | | Tensile modulus | 1445 MPa (ISO 527-2) | | Flexural strength | 30 MPa (ISO 178) | | Flexural modulus | 1225 MPa (ISO 178) | | Impact resistance | 14 KJ/m² (ISO 179) | | Max span (400mm centers) | 800mm | | Max span (600mm centers) | 600mm | | Fire rating | Class E (self-extinguishing) | | Temperature range | -20°C to +50°C (operational) |
Installation Guidelines
1. Joist Spacing
For residential decking with recycled plastic boards:
- Recommended spacing: 400mm center-to-center (for most deck boards)
- Heavy-duty applications (e.g., commercial, hot tubs): 300mm centers
- Diagonal board layouts: 300mm centers (increased load on joists)
2. Support Posts & Bearers
- Use stainless steel or galvanized brackets to attach joists to support posts
- Minimum bearer size: 100mm × 100mm (timber or recycled plastic)
- Post spacing: Max 1.5m for residential; 1.2m for commercial
3. Fixings & Fasteners
- Use stainless steel screws to prevent rust staining
- Pre-drill pilot holes (3mm smaller than screw diameter) to prevent cracking
- Countersink screws flush with joist surface
- Avoid overtightening—plastic compresses more than timber
4. Ventilation
- Maintain airflow beneath the deck (minimum 150mm clearance from ground)
- Avoid enclosed subframes—condensation can trap moisture against deck boards
5. Expansion Gaps
Recycled plastic expands/contracts with temperature changes:
- Leave 5mm gaps between joist ends and fixed structures (walls, posts)
- Do not butt joists tightly together—allow slight movement
Joist Span Tables (Safe Working Loads)
For Residential Decking (Live Load: 2.5 kN/m²)
| Joist Size | Joist Centers | Max Span | | ------------------- | ----------------- | ------------ | | 70mm × 47mm solid | 400mm | 600mm | | 70mm × 47mm solid | 600mm | 450mm | | 100mm × 50mm hollow | 400mm | 800mm | | 100mm × 50mm hollow | 600mm | 600mm |
For Commercial/Heavy-Duty (Live Load: 5.0 kN/m²)
| Joist Size | Joist Centers | Max Span | | ------------------- | ----------------- | ------------ | | 70mm × 47mm solid | 400mm | 450mm | | 70mm × 47mm solid | 600mm | 350mm | | 100mm × 50mm hollow | 400mm | 600mm | | 100mm × 50mm hollow | 600mm | 450mm |
Note: These are conservative estimates. For hot tubs, large planters, or other concentrated loads, contact our technical team for structural calculations.
Cost Comparison: Recycled Plastic vs Timber Joists
Typical Garden Deck (4m × 3m = 12m²)
| Cost Factor | Timber Joists | Recycled Plastic Joists | | ---------------------------------------------------- | --------------------------- | --------------------------- | | Initial joist cost | £120 (C16 treated softwood) | £240 (recycled plastic) | | Installation labor | £200 | £200 | | Maintenance (staining, inspections) | £50/year × 50 = £2,500 | £0 | | Joist replacement (rot damage after 10-15 years) | £320 × 3 = £960 | £0 | | Total 50-year cost | £3,780 | £440 |
Savings: £3,340 over 50 years (88% lower total cost)
Real-World Applications
1. Residential Garden Decking
- Most common use case: Elevated decks, ground-level patios, balcony decking
- Why it works: Zero rot risk means no surprise repairs; safe for children and pets (splinter-free)
2. Commercial Decking (Cafes, Pubs, Hotels)
- High foot traffic: Recycled plastic joists maintain structural integrity under heavy use
- Low maintenance: No downtime for staining or repairs—decks stay open year-round
3. Waterfront & Marine Decking
- Boardwalks, jetties, dock decking: 100% waterproof, never rots even when submerged
- Salt-resistant: Ideal for coastal installations (timber rots rapidly in salt spray)
4. Agricultural & Equestrian Structures
- Stable walkways, barn platforms, livestock pens: Non-toxic, safe for animals
- High-moisture environments: Performs flawlessly in wet farmyards
5. Municipal & Council Projects
- Public parks, playgrounds, council estates: 50-year lifespan reduces long-term budget strain
- Wheelchair-accessible ramps: Smooth, splinter-free surface meets safety standards
Why Choose Ezotrade Recycled Plastic Joists?
✅ 100% Recycled Material
We divert plastic waste from landfills and oceans—every joist sold supports the circular economy.
✅ UK-Based Supply & Support
Fast delivery across the UK, with technical support from our team of decking specialists.
✅ Trade & Bulk Pricing
Competitive pricing for contractors, councils, and large projects. Contact us for a quote.
✅ Custom Lengths Available
We can supply joists in lengths up to 6m—reducing the need for joins and improving structural integrity.
✅ Full Installation Guidance
Not sure about joist spacing or load calculations? Our technical team can help you design your subframe.
Get Started with Recycled Plastic Joists
Ready to build a deck that lasts 50+ years with zero maintenance?
Request a quote: Tell us your deck dimensions and we'll calculate the exact joist quantities you need.
Order samples: See and feel the quality of our recycled plastic joists before ordering.
Speak to our team: Call us for technical advice on joist spacing, span calculations, and installation best practices.
Ezotrade Ltd — Supplying 100% recycled plastic building materials across the UK.