Composite Decking Guide: Costs, Designs & Bohaiwood Tech

Composite Decking: Costs, Design and What the Specification Actually Means

Composite decking has moved from a premium niche to a mainstream choice, and the amount of marketing noise around it has grown faster than the useful information. This guide covers what the material is, what it costs, how to design with it, and how to read a specification sheet — with test report numbers where we have them and an honest gap list where we do not.

Chapter 1: Understanding the Material

1.1 What Composite Decking Is Made Of

Wood-plastic composite blends wood fibre with a thermoplastic polymer, usually HDPE. Our standard mix is approximately 60% recycled wood fibre and 40% recycled HDPE, plus UV stabilisers, pigments and processing additives. Treat wildly different ratios with suspicion — a board claiming 90%+ wood content behaves much more like timber, and one claiming mostly polymer is closer to plastic lumber.

The more important distinction is construction:

• Uncapped WPC — one extrusion, uniform through the section. Cheaper, more porous, stains and fades more readily.
• Co-extruded (capped) WPC — a polymer shell bonded over the core in a single pass. Ask how many faces the cap covers; four-sided capping leaves no exposed core.
• Hollow vs solid — hollow profiles are lighter and cheaper; stiffness comes from the internal rib layout and wall thickness, so ask for the cross-section rather than just the nominal depth.

1.2 The Numbers We Can Evidence

These are from third-party reports on our own profiles. Each one comes with the laboratory, the standard and the report number, because that is what a serious buyer asks for:

• Water absorption 0.80% (boiling-water test, EN 15534-4) — Intertek 240712130GZU-001
• Bending strength 29 MPa, modulus 3,400 MPa — same report
• Freeze-thaw: −1.7% strength change over three cycles — same report
• Linear thermal expansion 35 × 10⁻⁶/K — same report. This is the number your expansion gaps have to accommodate.
• Abrasion 28.2 mg/1000r (ASTM D4060) — same report
• Formaldehyde <0.02 mg/m³ (EN 717-1) — same report
• Surface burning Class A, FSI 10 / SDI 30 (ASTM E84-23c, white-faced co-extruded decking) — SGS GZIN2404000442CM01-1
• Reaction to fire B_fl-s1 (EN 13501-1, profile ZS140H25B) — SGS AJFTS26002282R02. That report states on its own face that it does not constitute a type approval.

UV ageing, full curve (ISO 4892-2 xenon arc, Weiput Shanghai SHA03-23102974-JC-01En): ΔE 0.53 at 500 h → 0.64 at 2,000 h → 0.96 at 3,000 h → 1.87 at 3,500 h → 4.58 at 4,000 h. We publish the whole curve deliberately. The rise after 3,500 hours is real, and a supplier who shows you only the 2,000-hour figure is showing you the flattering half.

Chapter 2: Cost and Budget Planning

2.1 What Drives the Price

Installed cost varies too much by region, labour rate and substructure for a single table to be honest. What reliably moves the number:

• Capped vs uncapped — the largest single material difference
• Hollow vs solid — hollow saves material cost and weight
• Substructure — often underestimated; joists, pedestals and fixings can rival the board cost on a roof terrace
• Volume and destination port — the factory-direct lever

Where composite reliably wins is over the ownership period: no staining, sealing or repainting, against a timber deck's recurring treatment cycle and earlier replacement. Run that comparison on your own local prices rather than a generic table — and be sceptical of any 25-year total-cost chart that cites a source you cannot find.

2.2 Buying Factory-Direct

Our minimum order is 70 m² for decking and 70 sets for fencing — well below the full-container minimum most factories quote. Samples are free; you pay the courier, and that cost is credited against your first order. For a real per-unit price we need the profile, colour, quantity and destination port.

Chapter 3: Design

3.1 Deck Steps and Stairs

Two directions worth knowing:

• Contrasting treads — a darker tread against a lighter deck field reads as a deliberate design move and improves step visibility, which matters more than it sounds at dusk.
• Integrated planter steps — build planter sidewalls from fence or cladding profile to tie the materials together. Line them and keep drainage away from the board ends.

On stairs specifically: check the local code for riser height, tread depth and handrail requirements before you design, and make sure the substructure under a stair is sized for point loads rather than treated like deck field.

3.2 Composite Cladding for Facades

Clip-fixed cladding installs quickly and gives a nail-free face. Design ideas that work: vertical runs to accentuate height, and mixing a smooth panel with a woodgrain board for texture.

One caution specific to cladding. Facade applications are where fire performance stops being a marketing line and becomes a code matter. Our E84 Class A and EN 13501-1 B_fl-s1 results are on decking profiles, and B_fl is a floor classification — neither is a wall-cladding rating, and neither is a CAL FIRE listing. For any clad facade, especially anything multi-storey or in a California WUI zone, confirm with the building official what evidence they require before ordering.

Chapter 4: Installation and Maintenance

4.1 Substructure and Fixing

• Joist spacing — follow the spacing for the specific profile; our standard decking centres are 350 mm. Close the spacing for diagonal layouts and at board ends.
• Fall for drainage — roughly 1:100 away from the building. Composite does not rot, but standing water encourages algae and stains.
• Expansion gaps — size them to the 35 × 10⁻⁶/K figure above and the temperature swing on site. This is the single most common installation failure, and it is excluded from most warranties.
• Hidden clips vs face screws — clips give a cleaner face and consistent gapping; face screws are faster to correct later. Do not over-tighten either: crushing the composite at a fixing creates a stress riser that cracks later.

4.2 Maintenance

• Rinse with a low-pressure hose. Keep pressure low — high-pressure washing damages a capped surface and is a common warranty exclusion.
• Clean along the grain with a soft brush and mild detergent. No sanding, staining or sealing.
• Inspect stair and railing connections annually, and re-tighten fixings that have worked loose.
• Dark boards run hotter in direct sun — that is physics, not a product defect, and no spray prevents it. Plan shade for barefoot areas.

Chapter 5: Sustainability and Certification, Stated Plainly

5.1 Recycled Content

The material is made from recycled wood flour and recycled HDPE, which diverts two waste streams, and a deck that lasts decades consumes far less material over time than one replaced every eight years. We do not publish a carbon figure per square metre, because we do not hold a verified product carbon footprint and an unverified one is worth nothing.

5.2 What We Hold — and What We Do Not

Held: ISO 9001 and ISO 14001 (IAS25924Q1473R0M, IAS25924E0394R0M, valid to April 2027); CE / CPR certificate M.2024.206.C97619 from UDEM covering three profiles; and the third-party test reports listed in Chapter 1 from SGS, Intertek and Weiput.

On CE specifically, the precise position: it runs under CPR Annex V System 4, a manufacturer's-responsibility route, and EN 15534 is not a harmonised standard under CPR. It is a declaration of conformity supported by notified-body documentation — not a mandatory passport for EU market access, whatever a supplier brochure may say.

Not held: ASTM D7032 and ICC-ES evaluation reports; CAL FIRE Building Materials Listing and SFM 12-7A-1; FSC or PEFC chain of custody; Cradle to Cradle; GREENGUARD; ISO 14067 carbon footprint verification.

If your specification needs one of those, say so at enquiry stage. Some can be commissioned, but testing takes weeks and none of it can be applied retroactively to a container already at sea.

Chapter 6: Choosing a Profile

Rather than a branded product table, the four questions that actually determine what you should order:

1. Capped or uncapped? Capped for anything in strong sun, near a pool, or where staining matters.
2. Hollow or solid? Hollow for weight-sensitive locations such as roof terraces and balconies; solid where impact and point loads are likely.
3. Colour. Expect a slight one-time settling of tone in the first months; choose from a weathered sample, not a screen.
4. Structural role. For anything load-bearing — a dock, a rooftop bar, a raised structure — the board specification is an engineering question. We will send section properties for your engineer; we do not publish a single load-capacity number, because span, fixing, orientation and duration all change it.

Getting a Real Quote

Send the profile, colour, quantity and destination port and you will get a per-unit price rather than a range. If you need a particular test report, name the standard and we will tell you plainly whether we hold it.