Specifying wood-based panels for structural use
Wood Information Sheet Section 2/3 Sheet 57. August 2005.
Since June 2002 it has been mandatory for manufacturers/suppliers of wood-based panels intended for ‘incorporation in a permanent manner in construction works’ to be able to demonstrate that their products, and therefore the structures they are built into, will comply with the Construction Products Directive (CPD). The CPD in the UK is implemented through the Construction Products Regulations 1991. The most straightforward route to achieving this is by complying with the so-called ‘harmonised Standard’ for wood-based panels, EN 13986, published in the UK as BS EN 13986: 2004 Wood-based panels for use in construction. Characteristics, evaluation of conformity and marking.
In all EU member states, apart from the UK, Ireland and Sweden, the only way to show compliance with the CPD is by CE marking. Although not compulsory in the UK, most wood-based panels intended for structural use are internationally traded and hence are likely to carry the CE mark. CE marking is described in more detail in the TRADA Wood Information Sheet 2/3-56 CE marking: Implications for timber products.
One of the reasons that the UK Government has not made CE marking mandatory is that it believes that there should be freedom to find alternative means of demonstrating compliance with the CPD. These alternatives are listed in The Building Regulations 1991 Approved Document to support regulation 7 – Clause 1.2. One of the options is an independent assessment and certification of fitness for purpose for a specific end use. In such cases specifiers should check that their intended use is within the scope of the certification for the product and should remember that substitution of the material specified with a similar material may not comply with the CPD.
Products outside the scope of BS EN 13986 may be CE marked through a European Technical Approval (ETA) using a European Technical Approval Guideline (ETAG) or a Common Understanding of Assessment Procedures (CUAP).
Note: For products covered by BS EN 13986, but not within the scope of the supporting product standards, eg because they have much higher properties, the manufacturer can apply the CE mark and declare his own specification values according to Table 14 of BS EN 13986.
BS EN 13986 refers to a series of BS EN product standards for specifications and requirements for each panel type. These set out minimum properties and quality control procedures for different grades of panel, defined by:
purpose: eg load-bearing or heavy duty load-bearing
service class conditions in which they are suitable for use: dry, humid or exterior.
The Technical Classes of panel suitable for use in appropriate structural (load-bearing) applications according to BS EN 13986 are shown in Table 1.
Table 1 Technical classes of panel listed in BS 13986 as suitable for structural applications.
Under BS EN 13986, manufacturers are required to have available a Declaration of Conformity and technical information on their product. These will include information on relevant characteristics as outlined below. Specifiers/purchasers should always obtain this information to ensure that the material being offered meets their requirements.
Performance characteristics
The required performance characteristics (properties) for panels in various applications are set out in BS EN 13986, although not all of the applications are structural. Structural components are listed under the following categories
internal use as structural components in dry conditions
internal use as structural components in humid conditions
external use as structural components
internal use as structural floor and roof decking on joists and structural wall sheathing on studs.
The performance characteristics may have been tested by the manufacturer and maintained through the production quality control process, or in some cases, standard values may be used.
Properties that must be assessed:
bending strength and stiffness (quality control tests)
bond quality/internal bond (quality control tests)
durability - moisture resistance, thickness swelling (quality control tests)
formaldehyde – a constituent of some adhesives, particularly aminoplastic resins (certain types of panel may not require testing if no formaldehyde-containing materials are added during, or post-production). For more details see BS EN 13986 Annex B
pentachlorophenol (only if materials used contain more than 5 ppm PCP). For more details see BS EN 13986 Clause 5.18.
Properties where standard values may be used:
reaction to fire (values for certain products mounted without an air gap are given in BS EN 13986)
water vapour permeability (values for certain products are given in BS EN 13986)
airborne sound insulation and sound absorption (values for certain products are given in BS EN 13986)
thermal conductivity (values for certain products are given in BS EN 13986)
characteristic values of strength and stiffness (values in BS EN 12369, see Design considerations, below)
mechanical durability – creep and duration of load (modification factors are given in BS EN 1995-1-1)
biological durability (guidance is given in BS EN 335).
Properties required for a particular end use:
Depending upon the end use, additional criteria also need to be defined:
BS EN 13986 requires soft body impact and concentrated load tests to be carried out, as described in BS EN 12871 Wood-based panels – Performance specifications and requirements for load bearing boards for use in walls, floors and roofs. Products that meet the requirements should be marked “FLOORING” or “ROOFING” as appropriate.
BS EN 13986 requires a soft body impact test (to BS EN 596) to be carried out against the requirements of BS EN 12871. Products complying with this should be marked “WALL SHEATHING”.
These performance-based tests for floors, walls and roofs are carried out on small sections of components and the results are only relevant to the construction tested (eg panel type and thickness, joist spacings). Such data must now be provided by the manufacturer. Part of the BS EN 12871 testing is for impact which is a pass or fail test, the other part is a point load test which will give the load category.
Note: BS 7916: 1998 Code of practice for the selection and application of particleboard, oriented strand board (OSB), cement bonded particleboard and wood fibreboards for specific purposes, which used to give thickness/span data for various panel types in floors and roofs, has been withdrawn and should not be used.
