What is a composite deck?
A composite deck is an outdoor surface made of WPC (Wood Plastic Composite) boards installed on a joist system. In simple terms - it is the same technology that has been proven on balconies for years, but applied to a larger area: a ground-level patio, a rooftop terrace, or an entrance platform.
Composite boards consist of approximately 60% wood flour and 40% polymer, supplemented with UV stabilizers and through-body pigments. The result is a material that looks and feels warm like wood, but does not rot, requires no oiling, and lasts over 25 years without maintenance.
The deck construction is straightforward: composite or aluminium joists are laid at regular intervals (usually 30 cm) on a levelled surface, and boards are mounted on them using mounting clips. The whole assembly creates a stable, ventilated floor that requires no drilling into the substrate and no adhesive.
Why composite boards instead of wood?
Wood on a deck is a classic - but also a source of problems. Even exotic species (bangkirai, ipe, cumaru) require regular maintenance, crack under frost, and turn grey without oiling. Domestic wood (pine, larch) fares even worse - 3 to 5 years and trouble begins.
WPC composite boards eliminate these issues:
- Zero maintenance - washing with a pressure washer once a season is enough
- Water absorption below 1% - wood absorbs 15 - 25% moisture, composite virtually none
- Frost resistance - withstands repeated freeze-thaw cycles without cracking
- UV stability - through-body colouring means the colour does not peel or turn grey
- No splinters - safe to walk on barefoot, which matters enormously on a deck
- Resistance to fungi and insects - the polymer provides no food for microorganisms
At BalkonSetup we use the same technology on balconies and decks. We install WPC boards on joists with clips - no drilling, no adhesive, with millimetre precision thanks to LiDAR measurement and CNC machining.
Composite vs wood vs tiles - what is best for a deck?
Choosing a deck material usually comes down to three options: composite boards, exotic wood, and ceramic tiles (porcelain stoneware). Each solution has its advantages - but also limitations that only become apparent after a few seasons.
| Feature | WPC composite boards | Exotic wood | Ceramic tiles (porcelain) |
|---|---|---|---|
| Maintenance | None - wash with water | Oiling 1 - 2x/year | Grout cleaning |
| Water absorption | < 1% | 15 - 25% | < 0.5% (porcelain) |
| Frost resistance | Full | Cracks with large temp. differences | Good (frost-resistant porcelain) |
| Anti-slip properties | High (dry and wet) | Medium, decreases with age | Depends on R class |
| Warmth underfoot | Warm, pleasant barefoot | Warm | Cold |
| Installation | Dry, clip-on (reversible) | Screws or clips | Adhesive + grout (permanent) |
| Durability | 25+ years | 10 - 15 years with maintenance | 20 - 30 years |
| Load capacity | Up to 500 kg/m² (on joists) | Comparable | Depends on substrate |
| Self-weight | Approx. 15 - 20 kg/m² | Approx. 18 - 25 kg/m² | Approx. 35 - 50 kg/m² (with screed) |
| 10-year cost (material + upkeep) | Medium | High (material + oiling) | Medium - high (grout, repairs) |
The key advantage of composite over tiles on a deck? Weight and installation. Ceramic tiles require a concrete screed, adhesive, and grouting - adding 35 to 50 kg per square metre. A joist system with WPC boards weighs 15 - 20 kg/m² and requires no interference with the substrate. It can also be disassembled without a trace.
Ground-level deck - what to look out for?
A ground-level patio is the most popular option. Composite boards are installed here on joists placed directly on a concrete substrate, spacer blocks, or adjustable pedestals. Each of these solutions works - the key is to follow a few rules.
Drainage and water run-off
This is the most important element of a ground-level deck. Water must have somewhere to go - if it pools under the boards, moisture, odour, and long-term substrate problems will appear.
- Substrate slope: minimum 1 - 2% (1 - 2 cm per metre) away from the building
- Gaps between boards: the clip system automatically provides 5 - 7 mm gaps through which water flows freely
- Open space beneath the boards: joists on pedestals create a ventilation gap of 3 - 10 cm - water evaporates, air circulates
- No sealed edges: deck borders should allow free water drainage
Under-board ventilation
Composite boards are practically waterproof (water absorption < 1%), but the substrate beneath them needs ventilation. A sealed, damp space is a breeding ground for mould and fungi - even if the boards themselves are resistant, the concrete substrate is not.
That is why the joist structure must ensure free airflow under the boards. The optimal under-board height is 5 - 10 cm. On ground-level decks where joists sit close to the ground, it is worth laying geotextile fabric underneath - it prevents vegetation growth while allowing water to pass through.
Substrate - what works?
- Concrete / screed: the best option - stable, durable, easy to level
- Paving stones: works, as long as they are stable and sloped
- Compacted gravel: possible with adjustable pedestals, but requires thorough preparation
- Bare ground: not recommended directly - a gravel layer + geotextile is necessary
Rooftop deck - installation specifics
A rooftop deck (flat roof) is an increasingly popular solution, especially in new multi-family construction. Composite boards work excellently here, but installation requires consideration of several additional factors.
Waterproofing is a priority
On a roof, beneath the boards, there is a waterproofing layer (bitumen membrane, EPDM membrane, or PVC sheet). It must not be punctured - no screw, dowel, or anchor should penetrate the insulation. A clip-on joist system is ideal here because installation is completely dry and non-invasive.
Adjustable pedestals
On rooftop decks, adjustable pedestals are the standard. They allow you to compensate for roof slopes, achieve a perfectly level surface for the boards, and maintain adequate ventilation space. Height adjustment range: typically 3 - 20 cm.
Wind and loading
On a roof, wind forces are greater than at ground level. Composite boards mounted on clips are stable, but in particularly exposed locations it is worth reducing joist spacing (20 - 25 cm instead of the standard 30 cm). The system's self-weight (approx. 15 - 20 kg/m²) is low enough not to overload the roof structure.
Technical specifications of composite deck boards
Before you decide on a specific material, it is worth knowing the numbers. Here are the key WPC board parameters we use on decks:
| Parameter | Value |
|---|---|
| Water absorption | < 1% (EN 15534 standard) |
| Frost resistance | Full - cycles from -30°C to +60°C without cracking |
| UV stability | Through-body colouring, colour warranty 10 - 15 years |
| Lifespan | 25 - 30 years (manufacturer warranty) |
| Fire class | Cfl-s1 (difficult to ignite, minimal smoke emission) |
| Anti-slip rating | R11 - R12 (safe even when wet) |
| Load capacity | Up to 500 kg/m² (at 30 cm joist spacing) |
| Board weight | Approx. 2.5 - 3.5 kg/lm (hollow profile) |
| Available lengths | 240 - 400 cm (CNC cut to size) |
How much does a composite deck cost?
The cost of a composite deck depends on several factors: area, shape, chosen board model, and substrate complexity. Approximate price ranges for a complete system (boards + joists + clips + tape + installation):
- Materials (without installation): approx. PLN 250 - 400/m² - depending on the board model and amount of cutting
- Professional installation: approx. PLN 80 - 150/m² - depending on the substrate and accessibility
- Total (materials + installation): approx. PLN 350 - 550/m²
For comparison:
- Exotic wood with installation: PLN 400 - 700/m² + annual oiling (PLN 50 - 100/m²)
- Outdoor porcelain tiles with installation: PLN 300 - 600/m² (with screed and grout)
Composite is comparable in purchase price, but wins decisively on 10-year costs - zero maintenance means zero additional expenditure after installation.
At BalkonSetup we quote each deck individually based on precise measurements. Our online calculator lets you get an estimated price in a few minutes - just enter your dimensions and choose a board model.
Why does BalkonSetup also build decks?
The name might suggest we only work with balconies - but the technology is exactly the same. WPC composite boards on a joist system with clips work identically on a 3 m² balcony, a 20 m² deck, and a 5 m² entrance platform.
What is more - our workflow is optimised for precise cutting and waste minimisation, regardless of the surface area:
- LiDAR measurement - we scan the deck with a 3D scanner accurate to the millimetre
- Computer simulation - our system simulates the joist and board layout, optimises cutting, and calculates materials
- CNC machining - boards and joists are cut by machine, not with a hand saw on site
- On-site installation - ready-made elements are mounted with clips, without drilling or adhesive
The same process, the same materials, the same precision - regardless of whether the area is 2 or 40 square metres. Only the scale differs, not the quality.
Frequently asked questions about composite decks
Do composite boards heat up in the sun?
Yes, in direct sunlight WPC boards can be warmer than, say, natural stone. Lighter colours heat up less. In practice, the temperature is comparable to wood - noticeably lower than with dark tiles or a metal structure.
Can I place a barbecue and heavy furniture on a composite deck?
Yes. With standard joist spacing (25 - 30 cm), the load capacity is up to 500 kg/m². A gas barbecue, a table with chairs, and even a jacuzzi - the system can handle it. For very heavy items, it is worth using protective pads under the legs.
How long does deck installation take?
A typical 15 - 20 m² deck takes a few hours to install at most. CNC-cut boards go up much faster than boards cut on site - everything fits right away.
Can I install composite boards myself?
Technically yes - the clip system is simple. But precise cutting and optimal joist layout require experience. Incorrect joist spacing means sagging boards. Poorly calculated cuts mean wasted material. That is why we recommend professional installation - or at least a professional measurement and design.
Summary - who is a composite deck for?
WPC composite deck boards are a solution for people who want:
- A warm, wood-look surface without annual oiling
- A floor resistant to water, frost, and UV - without sacrificing aesthetics
- Non-invasive installation - no drilling, no adhesive, fully removable
- A barefoot-safe material - anti-slip, splinter-free
- A solution that lasts 25+ years with no additional upkeep costs
Whether you are planning a patio by your house, a rooftop terrace, or an entrance platform - the technology is the same, and the result is the same: a durable, beautiful outdoor floor that simply works.
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