Question

We want to build a wooden deck. The timber merchant recommends teak, while the building materials supplier recommends wood-plastic composite (WPC) or fiber cement decking. We want the deck to be durable and environmentally friendly. Which material would you recommend?

Answer

Decking and balcony flooring are usually exposed to harsh weather conditions. UV rays, rain, hail, snow, and large temperature fluctuations can damage any material. In addition to the materials you mentioned, the following are available:

• Teak and other tropical hardwoods, such as bangkirai (yellow mahogany), cumaru (Brazilian teak), and ipe (Brazilian walnut), are highly durable and resistant. However, using these woods can negatively impact the environment and cause social problems. In addition to long transport routes, the exact origin and harvesting method are often difficult to trace. If you want to use tropical woods, make sure they come from reliable, sustainable sources, such as FSC-certified wood. Wood from your local region is generally more environmentally friendly. In some cases, however, certified tropical wood can be more environmentally friendly than regional wood due to its longer 30-year lifespan, despite higher transport costs.

• WPC (wood-plastic composite) is a material that consists of 50% to 70% wood fibers and plastics. It often contains additives, such as UV light blockers, binding agents, and color pigments. WPC offers the benefits of both wood and plastic, combining the appearance and stability of wood with the weather resistance and ease of care of plastic. With a durability of around 25 years, WPC rivals native hardwoods and tropical woods. However, it is usually not recyclable. The material often ages poorly, becoming brittle and discolored over time. For these reasons, we cannot recommend WPC from an ecological point of view.

• Fiber-cement decking, on the other hand, consists mainly of Portland cement, limestone powder, cellulose fibers, and polyvinyl alcohol (PVA) fibers. It also contains fillers and additives. This type of decking is highly durable and lasts 30 to 50 years. However, producing it is energy-intensive, and separating it into its components later on is impossible. Due to its long durability, we rate this material as neutral from an ecological point of view. Note that this material feels cold to the touch when there is no sunlight.

• Thermowood iswood that has been thermally modified, which involves heating it to at least 160°C in an oxygen-free environment. This process makes the wood less attractive to fungi and insects, thereby increasing its durability. The durability of thermowood depends on its quality (durability class 1 or 2), the type of wood, and the temperatures used. Thermowood typically lasts 20 to 30 years. We rate thermowood as neutral from an ecological point of view. Since softwoods, such as pine, are often used for this purpose, thermowood provides an alternative to weather-resistant hardwoods.

• Regional types of wood such as oak, black locust, larch, and Douglas fir are recommended by building biology. These woods are relatively weather-resistant, locally sourced, and easy to trace. When installed professionally – spaced with stainless steel wire and screwed from below, for example – they are comparatively durable and last 15 to 20 years. After use, the wood can be thermally recycled by burning it in a wood stove.

To maintain the appearance of decking materials and extend their lifespan, regularly clean them with water and a soft brush. In addition, keep the materials dry by avoiding shaded areas. In the fall and winter, clear them of leaves. We consider treating or caring for these materials with oils to be unnecessary.

For decks in heavily shaded areas without a roof or with an unfavorable north-facing orientation, we recommend using paving stones or natural stones. While stones are highly durable, they are cold to the touch, especially when there is no sunlight.

Josef Frey – Dipl.-Ing. in interior design, Baubiologe IBN, and a core member of the IBN team – answered this question.