Sustainability of Decking Materials: An In-Depth Analysis

Introduction

As environmental awareness increases, the sustainability of decking materials has come under scrutiny. Selecting a decking material involves considering factors such as durability, maintenance, cost, and importantly, environmental impact. In 2024 the sustainability information about construction materials continues to develop so that it can be considered in material selection.  This report delves into the sustainability of various decking materials, examining their environmental footprints, life cycle impacts, and the trade-offs associated with each option. The materials discussed include traditional wood, plastic composite decking, aluminium and Blazeboard mineral composite non-combustible decking.

Wooden Decking: The Traditional Choice

Wood has been the material of choice for decking for centuries, valued for its natural beauty, ease of use, and availability. However, the sustainability of wood decking depends largely on the species of wood used, the sourcing practices, the treatment methods and how long it lasts.

1. Environmental Impact of Harvesting:
   • The sustainability of wood decking begins with the source. Woods like tropical hardwoods such as balaua and teak are commonly used for decking. The environmental impact of these woods varies significantly. For instance, tropical hardwoods can often come from rainforests, where logging leads to deforestation, loss of biodiversity, and disruption of natural ecosystems. To mitigate these impacts, it is crucial to choose a source wood that is certified by organisations such as the Forest Stewardship Council (FSC), which ensures that the wood is sourced from responsibly managed forests.
   • On the other hand, softwoods like pine and fir, when sourced from sustainably managed forests, can be a more eco conscious option due to faster growth rates and lower environmental impacts associated with their harvest. However these softwoods don’t last as long, and need to be replaced sooner, so in the long term can be less sustainable.  See our Blog article on the lifespan of timber decking.
2. Carbon Sequestration and Embodied Energy:
   • One of the significant environmental benefits of wood is its ability to capture carbon. As trees grow, they absorb carbon dioxide from the atmosphere, storing it in their wood. When used as a building material, this carbon remains stored, reducing the overall carbon footprint of the material. However, the processing and transportation of wood do involve energy use, known as embodied energy, which varies depending on the distance the wood is transported and the energy efficiency of the transportation and processing methods.

3. Durability and Maintenance:
   • The durability of wood decking is another critical factor in its sustainability. Hardwoods like teak are incredibly durable and resistant to rot and insects, often lasting 25 years or more if cared for correctly. However, these benefits come with a high environmental cost if the wood is not sourced sustainably. Softwoods, while less durable, can be treated to extend their lifespan, but this often involves the use of chemical preservatives, which can have environmental and health implications. The maintenance of timber decking can involve specialist treatments, which are not always safe for non-specialists to use.
4. End of Life:
   • At the end of its life, wood decking is biodegradable and can be recycled or repurposed. However, treated wood, especially that treated with chemicals like arsenic or copper, poses environmental hazards and must be disposed of carefully to avoid soil and water contamination.

Composite Decking: A Mix of Materials

Composite decking, can be made from a blend of wood fibres and plastic, has gained popularity as a low-maintenance alternative to wood decking. This material is often marketed as a sustainable option due to its durability and the use of recycled materials.

1. Material Composition and Sourcing:
   • Plastic Composite decking typically contains a mix of recycled plastic (such as polyethylene or polypropylene) and wood fibres or sawdust. The use of recycled plastic helps reduce waste and the demand for virgin plastic, while the wood fibres often come from industrial waste products. This combination can reduce the environmental impact associated with raw material extraction and processing.
2. Durability and Maintenance:
   • One of the primary sustainability advantages of plastic composite decking is its durability. It resists rot, mould, and insect damage better than natural wood. Unlike wood, composite decking does not require painting, staining, or sealing, which reduces the use of chemicals and the associated environmental impact over its lifetime. However plastic decking can warp in warmer weather which can cause the walking surface to be not flat.
3. Embodied Energy and Carbon Footprint:
   • Despite its benefits, composite decking has a higher embodied energy than natural wood due to the energy-intensive processes required to produce plastic and combine it with wood fibres. However, requires less maintenance, the overall carbon footprint may be lower over the lifespan of the decking.
4. End of Life and Recyclability:
   • The end-of-life scenario for composite decking is more complicated than for wood. While some plastic composite decking manufacturers have recycling programs, the material is not as easily recyclable as pure wood or plastic. The combination of materials makes it challenging to separate and recycle, potentially leading to disposal in landfills.

Plastic Decking: Pure Durability with Environmental Costs

Plastic decking, made entirely from either virgin or recycled plastic, offers another low-maintenance alternative to wood decking. This type of decking is particularly popular in areas with damp conditions.

1. Environmental Impact of Raw Materials:
   • The environmental sustainability of plastic decking depends heavily on whether it is made from virgin or recycled plastic. Virgin plastic decking has a high environmental cost due to the extraction and processing of fossil fuels required to produce plastic. Recycled plastic decking, meanwhile, offers a more sustainable option by diverting plastic waste from landfills and reducing the demand for new plastic production.
   • The cutting of plastic decking can release microplastics into the environment, so it is important to consider where these cutting operations are carried out and make sure that swarf is collected and not released close to waterways and natural habitats.
2. Durability and Maintenance:
   • Plastic decking is highly durable against rot, splintering, and insect damage, and requires very little maintenance, which can contribute to its overall sustainability. However, its aesthetic appeal can be limited, as it often lacks the natural look and feel of wood or composite decking.
3. Embodied Energy and Carbon Footprint:
   • The production of plastic decking involves significant energy use, especially when made from virgin plastic. The carbon footprint of plastic decking is generally higher than that of wood or composite decking, primarily due to the fossil fuel-based nature of plastic. However, the use of recycled plastic can mitigate this impact, making it a more sustainable choice.
4. Recyclability and Disposal:
   • At the end of its life, plastic decking is theoretically recyclable, but the infrastructure for recycling large plastic products is limited. This often leads to plastic decking being disposed of in landfills, where it will persist for centuries. The challenge of recycling large plastic products remains a significant drawback to the sustainability of plastic decking.
5. Fire Safety:
   • Fire Risk makes plastic composites and virgin plastics unsuitable for apartments because the material can be easily ignited by discarded cigarettes etc, which can lead to rapid fire grown by flames up the building, as well as flaming droplets which can spread fire to the areas below simultaneously. Fire risk is assessed using the process described in our Blog article What is a Fire Risk Appraisal of External Walls (FRAEW)? – Blazeboard.  There are no treatments or coatings which can make a plastic composite or wood meet the requirements defined by EN13501-1 to make these materials suitable for high-rise residential construction.

Aluminium Decking

Environmental Impact of Production:

1. The production of aluminium is energy-intensive, with significant environmental impacts associated with mining bauxite, the raw material for aluminium, and the smelting process.
2. Energy use in the extrusion process can be broadly categorized into thermal energy (used for heating the billets) and mechanical energy (used for extrusion, stretching, and cutting).

Thermal Energy: Heating the aluminium billets accounts for a significant portion of the total energy consumption in the extrusion process.

Mechanical Energy: The hydraulic press used in the extrusion process for decking consumes a considerable amount of mechanical energy. The energy required for extrusion depends on the size of the press, the extrusion pressure, and the speed of extrusion. Higher pressures and faster extrusion speeds generally require more energy. Moreover, energy is also required for auxiliary equipment, such as pumps, compressors, and cooling systems, which support the extrusion process.

Cooling Energy: The cooling of extruded profiles can be energy-intensive, especially if water or air cooling systems are employed.

Finishing Processes: While finishing processes such as cutting, anodizing, and painting to give an attractive colour to the deck boards, can also consume usually gas and as such contribute to the overall energy use. The energy consumption for these processes depends on the specific finishing techniques employed and the quality requirements of the final product.

Durability and Maintenance:

• Aluminium decking is can durable if treated properly to make it resistant to rust, rot, and insect damage.

Recyclability and End of Life:

• Unlike wood, composite, or plastic decking, aluminium can be recycled indefinitely.

Blazeboard Mineral Composite Decking

Environmental Impact of Production:

1. The production of mineral composite uses mostly naturally occurring materials, combined with cement and re-enforcing fibres.
2. The production process occurs at a low temperature and so relatively small amounts of energy are used.
3. The production is a closed loop cycle where any offcuts produced during the process are re-cycled into the process.

Cooling Process: Since the production process is relatively low temperature, the materials cool naturally in air with no energy being consumed.

Finishing process: The finishing process is carried out by hand, with some power tools, and so the process utilises relatively small amounts of electricity.

Durability and Maintenance: Blazeboard mineral composite decking is extremely durable and will outlast timber or plastic composites.  This makes for a highly sustainable option.

Recyclability at end of life:  Re-use is always more sustainable than recycling.  Using a durable product means that it can be re-purposed if the building is demolished.  Blazeboard non-combustible mineral composite can be ground down and re-used in the production of new decking or in a range of end uses

Ultimately, the choice of decking material should consider both the immediate environmental impacts and the long-term sustainability over the life cycle of the product. By selecting materials that are responsibly sourced, durable, and recyclable, and by considering the specific environmental conditions and requirements of the project, homeowners and builders can contribute to more sustainable construction practices.