If you’re thinking about building an outdoor deck, choosing sustainable and environmentally friendly decking materials is an important consideration. However, assessing the eco credentials of the materials can sometimes be tricky.
When it comes to decking materials, timber decking may seem like the most environmentally friendly option, compared to the alternatives like plastic or composite decking. And while timber is a renewable and carbon friendly resource, there are some environmental downsides that should be considered.
So, let’s have a look at some of the environmental pros and cons of timber decking.
When ethically harvested from sustainable plantations, timber is a renewable and recyclable resource that benefits local economies while being environmentally friendly. Producing timber that is renewable and sustainable, however, requires long-term planning, investment and large amounts of land. Plantation forests must be properly managed, harvested and regenerated to ensure the end timber is sustainable and provides a net environmental benefit.
Low embodied energy
Embodied energy is the amount of energy required in the manufacture and processing of an end product. In general, the higher a product’s processing and manufacturing requirements, the greater the embodied energy. Products with lower embodied energy are usually better for the environment, as less energy and fewer resources are required in their manufacture.
Typical construction materials like concrete and steel have extremely high levels of embodied energy. Timber, on the other hand, has a very low level of embodied energy. It requires comparatively little processing to convert it from a natural resource to a usable timber decking product.
Forests and timber products play a vital role in carbon storage. A growing tree’s natural life cycle involves taking in carbon dioxide from the atmosphere and converting it via photosynthesis into oxygen. The carbon is then stored in the growing tree’s biomass. Approximately half of a living tree’s dry weight can be stored carbon. This means that Australian forests store about 10% of Australia’s greenhouse gases per year, according to the Forest and Wood Products Research and Development Corporation.
And the carbon benefits aren’t limited to just living trees. After a tree is harvested, the carbon remains stored in the timber for the life of the product. That means that timber decking will lock up the carbon in the timber for the entire life of the deck.
But it’s not all good news. While timber is a sustainable and renewable resource, those environmental benefits largely depend on the operation of the forestry industry.
Research suggests that the forestry industry and removal of trees through deforestation contributes up to 17% of greenhouse gas emissions into the atmosphere. Add to that the environmental effects of timber transportation, manufacturing and processing, chemical treatment and wood wastage, and you have a product that may not be as environmentally friendly as it first seems.
The effects of sawmilling and manufacturing
The sawmilling process involves converting harvested trees into usable timber products. The sawing, debarking, kiln drying and other processes release timber matter into the atmosphere, which can affect the air and water quality in the surrounding environment. Additionally, the heavy machinery required for the timber milling and manufacturing processes release a range of harmful gases into the atmosphere including carbon dioxide and carbon monoxide, sulphur dioxide and nitrous oxide.
Chemical treatment of timber
Timber production makes use of a wide range of harmful and potentially toxic chemicals. These include preservative treatments, adhesives and glues, and coatings like oils, stains and paints. While these chemical treatments are designed to increase the lifespan of the timber product (thereby reducing demend for new timber and offsetting the energy required for manufacture), they can be environmentally harmful during the manufacturing process. Additionally, these chemicals can be released into the environment when it comes to eventually disposing of the timber products.
Timber traceability can be tricky
Popular decking hardwoods, like merbau, have a troubling history of illegal logging and deforestation throughout South-East Asia, Papua New Guinea and other areas. Timber that is illegally harvested can come from irreplaceable old growth rainforests and there is rarely any regeneration and reforestation to replace the harvested wood.
Of course, not all hardwoods are harvested in this way. The Forestry Stewardship Council (FSC) is an international not-for-profit organisation that monitors the timber industry and certifies sustainable growers and suppliers. If an imported timber, like merbau, carries an FSC stamp, it generally means that it is ethically harvested and sourced from a sustainable supplier.
However, without this stamp, a consumer will have nothing more than the word of the supplier regarding the timber’s provenance and traceability. If you can’t be sure of the origin of your timber, then it could be contributing to rainforest deforestation.
Environmental effects of transport
While the processing and manufacture of timber products has a low embodied energy, that doesn’t take into account the environmental effects of the transportation required. Raw timber is a heavy and cumbersome product that requires significant transport resources. Moving the timber from the forest to the sawmill, from the sawmill to processor or supplier and from supplier to the end user is a fossil fuel-intensive process. And if you’re using a tropical hardwood sourced from overseas, then you need to factor in the environmental effects of international shipping as well.
Timber processing and manufacturing produces a lot of wood wastage. Abandoned logs, stumps and offcuts, branches and tree tops, and low-quality logs can be discarded during the harvesting the processes stages. Some of this wood can be used to power drying kilns or be further processed into low-quality wood products and engineered timber produces like medium-density fibreboard (MDF). The burning and further processing of these products can also release harmful gases and chemicals into the environment.
A timber deck and other timber products require significant maintenance over their life to keep them looking good and protect them from pests and the elements. Timber maintenance products can include chemical and petrochemical products like cleaners, sealer, oils, stains and varnishes. The ongoing maintenance requirements of timber can increase demand for environmentally damaging chemical products and add to chemical runoff in waterways.
What’s the alternative?
If you’re uncertain about the environmental suitability of timber decking, it’s worth looking into composite decking as an eco-friendly alternative. Premium composite decking is made from over 90% reclaimed timber and recycled plastics. It doesn’t contribute to deforestation and reduces the amount of waste wood and plastic that ends up in landfill. And for an engineered product, it has an extremely low level of embodied energy. It also has a much longer expected life than most timber products and doesn’t require the chemical maintenance that timber does.
Whichever material you choose for your outdoor decking project, it’s worth doing your research to ensure you end up with a deck that’s sustainable and environmentally friendly.
Julian is an editor and content creator with a background in industry journalism and technical writing. He’s an enthusiastic home handyman and gardener and collector of vintage books.