environment magazine

Timber testing – unpacking what is behind timber construction products

By Dr Ed Suttie, BRE

BRE is the UK’s largest research and consultancy business covering the built environment and all its facets. Dr Ed Suttie leads the timber and materials sustainability research in BRE. Using timber as the example, in this article he considers the array of testing behind a construction product that underpins the successful use and application in the industry in the UK.

Woodis an exceptional construction material. It is highly versatile, has good thermal properties and is strong and renewable. At a time when sustainable development is at the forefront of construction and key issues such as climate change dominate our future thinking, wood is an outstanding renewable material that offers a range of environmental benefits.

There are many different timber species and types of wood-based composite materials available, each with its own particular physical and mechanical properties. Correctly understanding these properties and how to specify, protect and maintain timber and wood-based products is key for delivery of effective performance in use.

Timber construction has entered a new era with architects and designers using the material in exciting and innovative ways. Current trends for greater sustainability, productivity and service-life performance have influenced product innovation and supply.

A window, looks simple doesn’t it? Actually it has had hundreds of thousands of pounds worth of testing invested in it by the materials and component suppliers as well as the joinery company. Construction product development can be a slow process with many years elapsing between concepts to product for the chosen few. For the purpose of demonstrating the range of testing that supports a product we have dismantled a wooden construction product and consider what was tested and assessed to enable its use in your home.

Timber properties

The fundamental mechanical properties of the wood species and the joinery blank that is manufactured from laminated and finger jointer wood need to be characterised. For example the properties of the wood species such as mechanical strength (static bending, compression, tensile) are presented as data determined using BS 373 “Methods of testing small clear specimens of timber”. The grading of the timber can then either be consider by visual grading or machine grading which then accounts for strength limiting features of the species and elements.

Case study: With funding from the Forestry Commission BRE’s testing laboratory is supporting the data capture to enable the machine settings for home grown Douglas fir and home grown larch timber to be generated. Thus opening more widely a market opportunity for these timbers into construction where they previously have not found application or application to date has been limited.

Creep and duration of load

For glued finger jointed elements the creep and duration of load character are tested to establish the permanent character of the glue line. In rooms of controlled temperature and humidity the glued sections are loaded and deflection movement is monitored over periods of weeks and months until the conclusive end point is reached.

Case study: Supporting an investigation by Coillte Panel Products into a revolutionary new MDF type product some of the earlier product applications where identified as those require long term mechanical stability. The product Medite Tricoya proved to have significantly better creep resistance properties that equivalent MDF type products. This offers application for MDF in end uses where this would have been a limiting factor.

End grain sealant efficacy

This tests a range of products such as sealants, glues and coatings to determine the relative contribution of end grain sealant to moisture protection for a joinery company. BRE use the British Woodworking Federation’s technical method to conduct these studies.

Case study: A coating manufacture in partnership with a joinery producer wanted to present to the market place a different proposition for a durable wood window. Instead of a use class 3 wood preservative treatment, they wanted to use a surface applied wood protection system including a coating and an end grain sealant to restrict moisture ingress to the joinery product. BRE conducted a series of tests on the contribution to moisture minimisation that the end grain sealant made and gave confidence in the continued development of the proposition.

Biological durability testing

The durability of the material selected to make a wood product is critical in being able to deliver a reasonable working life (as demanded by the Construction Products Directive) in that particular end use environment. A suite of European Standard tests are available for wood preservative treated wood, natural durability of timber species and panel products. Gaps in standards such as that for wood modification technologies (BRE Digest 504) require expert adaptation of existing methods. The laboratory and field tests require pure cultures of fungi and breeding colonies of termites and wood boring beetles to be able to conduct the tests.  The retention required of the wood preservative to be effective at protecting against biological deterioration caused by fungi and insects.

EN113: This European Standard specifies a laboratory test method which gives a basis for the assessment of the effectiveness of a wood preservative against wood destroying basidiomycetes. By using this method it is possible to determine the preservative retention at which impregnated wood of a susceptible species may be regarded as adequately protected under the conditions of test. EN113 with relevant preconditioning is the cornerstone test standard for wood preservative products in Europe. With this critical value (effective retention) the product could enter the market with a efficacy claim.

EN46 tests against Hylotrupes bajulus (House longhorn beetle) larvae and EN117 and EN118 against Reticulitermes (European subterranean termites).

In addition to the efficacy of the treatment the environmental assessment of the treated wood must be considered for submission of products under the Biocidal Products Directive. This is assessed as part of leaching studies using either CEN or OECD methods to provide dossier information for the treatment. BRE can conduct the environmental performance studies required for BPD registration of wood preservatives for a formulation - recording losses of preservative to water following standard OECD guidelines or CEN/TS 15119 methods. This is conducted using EN113 sized treated wood specimens and data is typically gathered over a 6 week leaching period or longer.

Case study: On-going testing for two of the world’s largest wood preservative manufacturers includes laboratory assessment and field testing. The BRE Building Technology Group works to ISO 17025, ISO 9001 and ISO 14001 Standards and is accredited by UKAS to perform the following efficacy testing against wood destroying fungi, termites and wood boring insects. BRE has the only independent UKAS accredited biological test facility in the UK with full breeding colonies of house longhorn beetle and termites.

Emissions testing

All construction products emit chemicals to the air. For those materials for use in indoor environments this is an important issue as the emission is released to the indoor air. In order to maintain the health and well being of the occupants of the building, avoid any smells, these emissions are quantified and can be managed to within world recognised healthy limits.

Case study: Investigation of odours in new clothes cupboards in an office building, staff had complained about bad odours from a cupboard used to store clothes, air sampling from the cupboards and office revealed unusually high levels of fatty acids in the cupboards. FLEC emission measurements (BS EN ISO 16000-10) from a sample of the shelf material in the cupboard conclusively proved that the smell was due to the cupboard material.

Case study: Investigation of complaints about a strong “chemical” smell in a basement room, on site sampling revealed high levels of formaldehyde in the air. Emission measurements using BS EN ISO 16000-10 adapted for formaldehyde from a sample of plywood taken from the room demonstrated that the high levels of formaldehyde could be explained by the measured emission from the plywood.

Coating weathering testing

The performance of the exterior wood coating on the window is key to the maintenance interval needed for the product and the acceptance of the system in the market place. Fully factory finished wood windows are widely available now and offer the consistency and reliability of a factory produced and coated product. To assess the performance of wood coatings we undertake EN927-5 tests of artificial weathering of coated wood specimens in QUV weathering machines that simulate UV conditions of sunlight and moisture to accelerate the degradation experienced. During exposure the samples are assessed for colour stability, adhesion of the coating and other defect characteristics. The other longer term test is EN927-3 the natural weathering performance for exterior wood coatings is assessed over a one year period to inform on the suitability as exterior coatings.

Acoustics and Sound Insulation

Acoustic conditions are a key issue for occupants of any building from schools to hospitals, our homes to supermarkets. Failing to achieve a client’s expectations or statutory requirements leads to complaints and has been linked with dissatisfaction and adverse health effects for the building occupants.

With the pressures to develop buildings in close proximity to major traffic links, it is inevitable that the external building elements will be exposed to increasingly higher levels of noise. Without appropriately specified fenestration, the internal noise environment can become an undesirable place to live or work.

Design teams need accurate facts and figures relating to products such as windows to give them confidence that the proposed solution complies with statutory or employer’s requirements. Independent laboratory tests of sound insulation to BS EN ISO 140-3, within a purpose built UKAS accredited testing laboratory, provide a consistent and readily comparable performance measure. Suppliers of products tested to these standards set themselves ahead of the competition, whilst design and purchasing teams can specify tested products with confidence.

Weather tightness

The overall weather tightness of the whole window is tested.  The window is fitted into a special rig that creates pressure on one side of the window that is then sprayed with water simulating driving rain. This helps manufacturers understand how the whole product works and helps them assess, improve and develop the performance of their windows, doors and rooflights. The BRE team assess, test, inspect or investigate with regards to weather tightness, air permeability, water tightness, wind resistance, operation, strength, air tightness, air flow characteristics, impact resistance, security testing and CE Marking.

Environmental product declaration (EPD)

Timber from a sustainable and legal source is a hugely credible carbon store and a capable construction product, be it as cross laminated timber (CLT), a window, a box beam or a solid hardwood floor. An EPD is a means of a company communicating the environmental impacts of a product in a uniform and considered way. The EPD is under pinned by a comprehensive Life Cycle Inventory and assessment to capture the impacts through from cradle to grave or cradle to cradle to cradle. In the UK the boundaries of the LCA method and the way the impacts would be assessed, weighted and summarised was agreed in the mid 1990s by all sectors and provided the basis for the Green Guide to Specification (BRE publication and on-line www.thegreenguide.org.uk). The Green Guide underpins the materials component of the regulatory framework for delivery of low impact construction in the UK using BREEAM and the Code for Sustainable Homes. The Green Guide independently demonstrates the environmental credentials of construction products and enabling specifiers to compare impacts for different solutions and select the lowest impact ones.

Service life performance

Service Life Prediction or Planning is a process that seeks to ensure, as far as possible, that the service life of a building will equal or exceed its design life, while taking into account (and preferably optimizing) its life cycle costs (ISO 15686-1). The building sector in the UK is under pressure to improve its cost effectiveness, quality, energy efficiency, environmental performance and reduce the use of non-renewable resources. A key issue for the competitiveness of wood is the delivery of reliable components of controlled durability with minimum maintenance needs and life cycle costs.

A first attempt has been made at a predictive model delivered by the pan-European R&D project “Woodexter” including BRE. It is a simple tool that connects climate, moisture, building, design, sheltering, consequence of failure, resistance of the material to indicate whether a satisfactory service life will be reached. A guideline and tool for decking and cladding is available for downloaded (www.kstr.lth.se).

CE marking

CE marking is a declaration by the manufacturer that the product meets all the appropriate provisions of the relevant legislation implementing certain European Directives. A wood window is a high complex product. For a wood window to be CE marked it would include typically the depth and breadth of testing that has been described above and most likely additional studies of glue bond strength, gasket performance, metal fixing and fastenings performance all to the recognized European standards.

CE marking is currently carried out using the Construction Products Directive (CPD) with reference to a harmonised product standard (hEN), currently it is not mandatory in the UK. However, the European Commission and UK Government adopted the Construction Products Regulation (CPR), on 4 April 2011, which will replace the Construction Products Directive (CPD). The main provisions of the CPR will not come into force until July 2013, which will in effect make CE marking mandatory for construction products covered within each of the EC mandates. This will have major implications for UK manufacturers, designers, specifiers and regulators as CE marking will be mandatory in the UK for a number of construction product types. The core principle is that CE marking should give companies easier access into the European market to sell their products without adaptation or rechecking. It is a widely recognized and accepted mark. BRE works with clients to support them and develop the package required to achieve CE marking for their products.

About BRE

BRE is the UK’s leading centre of expertise for construction, the built environment, sustainability, energy, fire and many associated issues. We provide research, consultancy, information and testing services to customers worldwide. www.bre.co.uk  BRE is owned by the BRE Trust, a registered charity (no. 1092193) with a mission to champion excellence and innovation in the built environment for the benefit of all. www.bretrust.org.uk

BRE has comprehensive, integrated capabilities for timber and construction related research and consultancy. We are involved in projects ranging from the evaluation of the sustainability of wood products and properties of newly available species, to the structural performance, service life and behaviour of modern products.

BRE’s extensive knowledge and involvement in innovative projects means that we can provide cutting-edge support and advice throughout the timber life cycle, including:

-       Processing: best practice and innovation in sawing, kiln drying, machining, grading, scanning, edge jointing

-       Engineering: develop and measure the performance of structural timber and timber products and conduct site investigations

-       Specification: the behaviour and long-term performance of different wood species and wood composites including environmental aspects, life-cycle analysis and structural behaviour

-       Wood performance: durability of wood and wood products, the use of wood protection and durability enhancing technologies including exterior coatings to enhance performance, causes of and how to prevent deterioration, service life attainment

-       Resource efficiency and management of timber: local sources of timber, innovative applications, recycling and reuse of timber and timber products

A complete review of BRE’s services can be found at www.bre.co.uk and to source BRE publications see www.brepress.com

For further information please contact Ed Suttie Tel: 09123 664000  Email: This email address is being protected from spambots. You need JavaScript enabled to view it. "> This email address is being protected from spambots. You need JavaScript enabled to view it. or visit www.bre.co.uk/timber