Specifying sustainable timbers

In order to use timber, or indeed any other material, successfully the designer/specifier has always had to ensure that two criteria are met:

1 Does the species I have selected have the right mix of material properties for the end use?

2 Has it been processed in the correct manner for that end use?

To this gratifyingly short list we now add a third item:

3 Is the timber that I have specified from a sustainable source and can it be proved?

On the face of it these are three very simple questions that could answered Yes, Yes and Yes! Unfortunately, life is not that simple and providing the correct answer to each question involves just a little more work.

For most end-uses (eg. structure, joinery, furniture and flooring) and species combinations, information is readily available in documents published by TRADA, FIRA and others. British Standards also offer plenty of useful advice and certainly offer the cautious specifier a straightforward specification route. In addition, many timber suppliers are also able to provide quite detailed guidance on the properties and processing history of the material they supply.

Such information gives the specifier guidance on a wide range of material and processing properties including, density, dimensional stability in use, ease of drying, natural durability, permeability, strength, texture and colour. By cross referencing this against the characteristics considered desirable for a particular end-use the specifier is directed towards a short-list of appropriate timber species.

As an example of how this works in practice it may helpful to consider the following simplified example:

An engineer wanting to specify a timber for use in the piles of a pier or jetty knows, from her calculations, that she needs a timber with a bending strength of at least 16 N/mm2. The end-use requires a timber that is either naturally (very) durable or treated with a preservative, resistant to attack from marine borers and available in long lengths. The timber does not need to be dried as it is being used outside and its colour and texture etc are of little interest.

Under these circumstances, the structural code of practice, BS 5268: Part 2, directs the engineer towards the following:

The requirements for a timber that is naturally durable or very durable, resistant to attack from marine borers and available in long lengths rules out balau, kapur, karri, kempas, keruing and merbau and leaves, using BS 5268: 2 as the guiding document, only ekki, greenheart and opepe. When specified in line with BS 5268: Part 2 these timbers would all give good performance.

However, for a variety of very valid reasons, including most importantly a desire to use timber sourced from a sustainable resource, clients, contractors and specifiers may not want to use or be restricted to such a short list of timbers. Moreover, for project specific practical reasons it may not be possible to use one of the three timbers identified above.

As already indicated, in addition to the traditional issues of performance, price and availability, the choice of materials for construction projects is now influenced by environmental concerns – and if timber cannot demonstrate its undoubtedly excellent credentials - it will lose out in the marketplace. Today, sustainable production has to be proved and the proof lies in third party certification. This is a two-stage process:

Forest management certification involves the independent third-party certification of forest management practices according to a set of standards which are measured against actual practice. Wood product certification involves a verification of the chain of custody “from forest gate to finished product” and aims to prove that a wood product bearing a label lives up to the claims being made on that label. The two major players in this market place are the Forest Stewardship Council (FSC) and Pan European Forest Certification (PEFC).

FSC have drawn up a list of 10 principles which organisations must follow if they are to secure certification. FSC does not conduct certification itself but accredits certification bodies eg. BM TRADA Certification to undertake the assessment of forest and timber processing operations on its behalf. In a similar fashion PEFC has created a framework where credible certification schemes eg the Finnish Forest Certification System (FFCS) might gain mutual recognition and secure market access without being controlled by the FSC.

So, on the face of it, even when proof of sustainability is taken into account timber specification is apparently a simple issue. The solution is to find supplies of the timber species already identified by the technical specification and ensure that they carry the appropriate forest management and chain of custody certification.

Unfortunately, this is where we find that life is frequently not that simple. At present, the PEFC only certifies timber from European forests (there are plans to expand activities to forests outside of Europe in the near future) and in even the simplified specification model given earlier no European timbers have the required combination of properties. This means, that if the client, specifier and/or contractor want to use timber produced from a sustainable resource and also want to prove it then they must ask for timber that carries the FSC logo.

This can be where things start to get a bit more complicated. The supply of FSC timber is such that not all species are available all of the time and there is a chance that none of the species (ekki, greenheart or opepe) will be available in the size and length combinations required. However, all is not lost, as other material, perhaps from “lesser known” timber species, not recognised by the documents used to create the original specification (ie BS 5268: Part 2), may be available from certified sources. All that needs to be done now is to prove that these species are up to the job – Simple!

However, solving one problem can sometimes just create another. By definition, “lesser-known” timber species are exactly that – lesser known. Good quality, reliable, technical information on their properties and performance can be difficult to locate and in a few cases may not exist at all. This is where we can help, TRADA Technology’s team of expert timber technologists have access to an extensive, up to date and continually growing library of technical information that covers timbers from aba to zundu and most of those in between. We regularly provide advice and information to suppliers, clients, specifiers and contractors on the selection, specification and selection of “lesser-known” timber species help to ensure that where these timbers are used the risk of problems or failures are eliminated.

Ultimately, it remains a relatively simple three step process to specify timbers that come from a sustainable source – but the emphasis may have to change:

1 Identify timber species that are available from a sustainable source

2 Select the species with the right mix of material properties for the end use under consideration

3 Confirm that the species selected can be processed correctly to deliver those properties.