Landscapes in themselves are a key infrastructure for a sustainable built environment. As environmental stewards, it is the professional responsibility of Landscape Architects to ensure that the places we create are built in ways that further the larger sustainability goals that include reducing emissions, zero-waste and conserving forest reserves around the world. In this article that discusses sustainably built landscapes, let’s talk about materials.
The natural choice for many landscape elements, the choice of hardwood impacts the care of forest reserves that are important carbon sinks for the world. Hardwood species listed in the International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species (www.iucnredlist.org) as endangered or worse should be avoided. Notorious in tropical Singapore is the use of Chengal which is classified as endangered by IUCN, in outdoor deck application. Merbau, which is listed as near threatened, is a more acceptable species that has similar, if not better, physical properties compared to Chengal. If “near threatened” sounds bad, note that in the classification spectrum used by IUCN, near threatened is one step up from least concern.
For more information on the red list categories, visit https://www.iucnredlist.org/resources/categories-and-criteria
Merbau has a known “bleeding” problem which poses stain issues, but it can be addressed by soaking in solvents to remove the tannin and sealing the timber. Where it is inevitable to use Chengal, use source tracking services to ensure that the timber is sourced from known, legal, healthy and well managed forests. Double Helix Tracking Technologies is one of such companies offering source tracing, forest assessment and verification services for sustainable sourcing of timber.
Other timber species can also be explored apart from Merbau. Grab a copy of “100 Malaysian Timbers” published by the Malaysian Timber Industry Board to browse tropical timber available in the region, research their conservation status, and speak with one of the four local timber mills to tap into their knowledge of the various timber, their properties, availability and such. Also find out what products are available for anti-termite, anti-fungus and preservative treatment, and avoid those that have adverse environmental and human impact like Copper Chrome Arsenate (CCA), as arsenic, a known human carcinogen, can seep from timber treated with such, into soil and water.
Make sure that the timber sourced is certified by Programme for the Endorsement of Forest Certification (PEFC) or Forest Sustainability Council (FSC). Either one of these certifications suffice.
Mass Engineered Timber (MET)
A green alternative to steel and concrete, MET, the collective reference to Glulam and Cross Laminated Timber (CLT) can be considered for the building of bridges, visitor centres and shelters. MET is manufactured from fast-growing soft wood like Poplar, Spruce or Pine from plantations, heat and pressure treated, and laminated to form lumber with high structural strength. Softwood can be harvested after 15 years of growth, a much shorter period compared to tropical hardwood species that takes up to 5 times longer to mature. The carbon absorbed by the trees get stored in the lumber used for infrastructure, making it a good means to de-carbonise. You can find a list of suppliers and contractors who worked on MET projects in Singapore on BCA’s website.
Bamboo Veneer Lumber (BVL)
BVL is a patented technology developed by ETH-NUS, and is in the early stage of being commercialised by Widuz. It is a ground breaking technology that enables engineered bamboo to be used for structure, making the proposition of bamboo as the green steel of the future a reality. Bamboo grows 5 times faster than timber, and can be harvested in 3 to 5 years of growth, enabling it to remove carbon from the atmosphere at a much greater rate than softwood timber used in MET. The lumber has 3 times more strength than MET which enables smaller structural members to be designed. Look out for this one, when it is made available in the market.
You can learn more about BVL from www.widuz.com.
Composite timber, composite bamboo and Fibre Reinforced Plastic (FRP)
In deciding materials for decks, composite timber, bamboo and FRP can be considered as alternatives for hardwood timber. A huge range of products exists in the market, differentiated by the proportion of timber or bamboo fibres incorporated. Most such products have obtained the green label issued by the Singapore Environment Council, which ensures a certain degree of contribution towards sustainability in their use. There is no need to shy away from products that are completely plastic and do not contain any natural fibres. A key aspect of sustainability is achieving zero-waste and circular economy. To get there, robust and durable materials with mammoth lifespan, and those that can be recycled play a huge part in the game.
Hardwood timber decks have a lifespan between 5 to 10 years, increasingly observed to tend towards the lower end as trees are harvested before maturity to supply the high demand. Alternatives like FRP which is corrosion, UV and weather resistant have a lifespan of 25 years or longer, and is robust, requiring hardly any replacement, is a sensible choice for high use public spaces and ideal for reducing waste going to our limited landfill. FRP is also lightweight, requiring less materials for foundations and supporting structures.
An increasing popular composite is Cellwood, made of purely Thermoplastic elastomer (TPE), manufactured without formaldehyde, and is heavy metals-free and complete recyclable. Its anti-slip surface performance is much better than hardwood timber, and because it is purely plastic, it is very durable in high moisture environment making it suitable for use in structures over water bodies. And the best thing is, no one can tell it’s not timber.
About the Author:
Abby Ng is a Landscape Architect, architectural designer and urban thinker with more than a decade’s practice at National Parks Board Singapore, having directed the design and development of major green spaces including Jurong Lake Gardens, Sungei Buloh Nature Parks network parks in Singapore. A keen advocate for sustainability, she pioneers the adoption of new technologies in sustainable materials, waste to energy systems, mobility, circular economies and decarbonisation in the built environment.