Assessing the environmental impact of treated timber
There is a growing focus on how treated timber performs against more carbon-intensive materials, and untreated timber, across its entire life cycle. Dr Steve Uphill demonstrates the application of the Life Cycle Analysis (LCA) ‘ReCiPe’ method to assess treated timbers for data-led decision making.
Wood preservatives are used to enhance the natural durability of certain timber species, helping to provide protection from decay fungi and insect attack so that the timber can be used in commercial applications. Water-based or oil-based wood preservative is industrially applied through an impregnation process so that it bonds with the timber’s fibres, making wood more durable. For example, European homegrown softwoods that play such an integral role in capturing and storing CO2 from the air, such as spruce and pine, have little natural durability. This means that unless treated, they are unsuitable for applications exposed to weathering (rain, moisture), or near ground level and in the ground.
Like any construction material, wood preservatives are continually evolving with specifier and regulatory demands. While the ultimate aim is to provide long-term protection against decay fungi and insects for less durable timber
species, this must be done in a way that minimises any risk to the environment, or human and animal health. With a wide choice of construction materials available in the marketplace, investment in Environmental Product Declarations (EPDs) and Life Cycle Analysis (LCA) provides designers and construction professionals with the information they need to make informed choices on whether treated timber is the best material option.
In this article I will summarise how wood preservatives are regulated and then explore the current landscape of actives used in formulations. With a focus on the use of organic actives, I will look at the applicable end-uses of treated timber in accordance with BS EN 335-1 Durabiltity of wood and wood-based products. Definitions of use classes – General. To evidence how treated timber can compare with other construction materials, I also include a recent Life Cycle Analysis study, which will help illustrate the type of data that is available.
The regulatory landscape governing wood preservatives
The development, production and use of wood preservation products is regulated in the EU under the Biocidal Products Regulation No 528/2012 (BPR).1 This regulation aims to improve the functioning of the biocidal products market in the EU, while ensuring a high level of protection for humans, animals and the environment.
Under the BPR, authorisation of biocidal products is a two-step process. Firstly, all active substances contained in a product have to be approved at EU level, following assessment of hazardous properties and possible risks. In the second step, biocidal products are evaluated before being authorised. >>
The BPR requires data on the possible exposure and toxicity to humans such as reproduction toxicity, carcinogenicity, or endocrine disruption etc, as well as data on environmental impacts such as accumulation in soil or ecological toxicity.
It also introduces formal exclusion and substitution criteria which apply to the evaluation of active substances. When an active substance is approved, it is granted for a defined number of years. The maximum number of years granted before renewal is 10 years.
In the UK and Northern Ireland, following the UK’s withdrawal from the European Union, GB BPR is in place. GB BPR mirrors EU regulations in large sections but is an independent regulation overseen by the UK Health and Safety Executive.
When developing a new wood preservative it is vital that the regulatory status of available active substances is understood. The BPR process requires substantial investment, involving stringent risk assessments, as well as generating extensive data and studies to prove that the wood preservative is effective against wooddestroying fungi and/or insects. The longevity of authorisation of an active substance is key for these efforts to be successful.
The evolution of actives used in wood preservatives
Across Europe there are a number of water-based wood preservatives available, and a handful of oil-based. When specifying treated timber, it is important to understand how the chemistry behind the wood preservative is suited to the timber’s end-use application. The eventual end-use of preservative treated timber is classified into one of five categories(Figure 1). These ‘Use Classes’, defined in BS EN 335-1, are based on the potential threat to the timber from decay or insect attack in its eventual application.2
Treated timber used in Use Classes 1 and 2, where there is less exposure to wetting such as roofing battens and frame timber, is transitioning across Europe to non-metal preservatives that are based on organic actives. These wood preservatives tend to be low-pressure impregnated to provide an envelope of protection around the timber. Some would put the case as to why internal joinery with little risk to wetting needs to be pressure treated. While the level of risk to wetting is low, these are important components to structural integrity and by using treated timber, longevity and durability will be assured. There are products available that are both metal-free and VOC-free. Timber treated with low-pressure water-based wood preservative that uses organic actives can be reused or recycled at end of life (subject to local waste regulations).
For Use Classes 3(c) and 3(u) – coated and uncoated –non-metal-based wood protection technologies are being developed that can be applied through high-pressure impregnation. However, it is worth noting that in Use Class 3(u), where the treated timber is uncoated and above ground level, these new metal-free technologies will provide a lower service life than the more traditional copper-based wood preservatives. An example would be cladding where a metalfree high-pressure wood preservative would provide roughly 15 years’ worth of protection, whereas copper-based wood preservatives would provide between 20 and 25 years.
In the higher-risk Use Class 4 application, where the treated timber will be in contact with ground or water, water-based wood preservatives containing copper are the most fit for purpose. However, not all copper-based wood preservatives utilise the same actives, which means that different formulations will have different overall environmental impacts. To help timber manufacturers provide a cradle-to-grave environmental assessment of their products, wood preservative manufacturers are being asked to invest in Environmental Product Declarations (EPDs) for all of the brands that they produce. >>
“To help designers and construction professionals truly create sustainable buildings, wood protection technologies must continue to look to actives that consume fewer resources, eradicate waste at landfill at end of life, and have minimal impact on the environment.”
Assessing the whole carbon impact of treated timber: a case study
At Arxada we are investing in both EPDs and Life Cycle Analysis (LCA) for our wood protection technologies. Not only is this critical when comparing treated wood with alternative materials, but also helps evaluate untreated vs treated wood. If treated wood provides longevity and durability, and requires minimal maintenance, then this has a positive impact on the whole carbon footprint.
The most recent LCA I have been involved with is that for Tanasote®, a BPR authorised oil-based copper wood preservative that is a modern alternative to traditional creosote treatments For this project, the LCA ‘ReCiPe’ method was adopted, covering analysis of the following three categories for end use applications such as railway sleepers and utility poles: (i) damage to ecosystem, (ii) damage to human health and (iii) damage to resources (Figure 2). A sensitivity analysis was also completed to assess the influence of agricultural land occupation and terrestrial land transformation as part of the LCA.
The direction of travel for wood preservatives
With VOC-free and metal-free options now available, and with some copper-based preservatives using such small quantities of copper due to being paired with powerful organic co-biocides, the wood protection industry has certainly evolved. However, the industry cannot be complacent and must continue to invest in educating the market on its progress, to help dispel outdated misconceptions about the use of treated timber.
To help designers and construction professionals create truly sustainable buildings, wood protection technologies must continue to look to actives that consume fewer resources, eradicate waste at landfill at end of life, and have minimal impact on the environment. Significant investment in testing these new formulations will be key to success, demonstrating how the protection technologies perform in the real world n
About the author
Dr Steve Uphill Technical Lead Wood Protection, Americas, EIMEA and Industrial Arxada
References
1. https://echa.europa.eu/regulations/ biocidal-products-regulation
2. https://www.thewpa.org.uk/ preservative-treatments
“With a wide choice of construction materials available in the marketplace, investment in Environmental Product Declarations (EPDs) and Life Cycle Analysis (LCA) provides designers and construction professionals with the information they need to make informed choices on whether treated timber is the best material option. ”