Plywood is a widely used and well proven construction material made from a combination of wood veneers and resins. Oriented Strand Board (OSB) is an alternative to plywood in a variety of structural and nonstructural applications. It is made from long strands of wood bonded together with a synthetic resin adhesive. Both products are available with full structural data and sustainable credentials.
For more information on plywood and OSB please take a look at the Panel Guide which is free to download at http://www.ttf.co.uk/Timber_industry/Panel_Guide.aspx. This TTF Guide provides information on the different types of constructional panel products available and what to look for when specifying them.
Specifying Constructional Plywood
There are two types of Constructional Plywood:
Both types of constructional plywood can be used in the three end use classes for plywood defined in the European Standard EN 636 as shown in the table below. The standard specifies the requirements for plywood for general purposes or structural application in dry, humid or exterior conditions.
The most common types of plywood available for use in UK construction are structural plywood for humid uses (EN 6362 S) and general plywood for humid uses (EN 6362 G). These types of plywood are made from durable resins which are suitable for most construction uses.
Plywood for Exterior use is also available but may be less cost effective as both the resins and the wood veneers within the product must be durable in the long term. There is also a special type of exterior Plywood called Marine Plywood which has its own British standard BS 1088 2003, and as the name suggests must be durable enough to endure regular exposure to extreme weather conditions. However, Marine Plywood rarely has proof of strength performance provided by the supplier and so should not be used load bearing construction uses, unless this strength data is provided.
As with all timber products, plywood should be certified sustainable or show proof of legal origin. This can be done easily via certification schemes like FSC (Forest Stewardship Council) or PEFC (Programme for the Endorsement of Forest Certification). Where these schemes are not available there are other ways to show sustainability or legality. For more information on certification and third party schemes please visit the TTF Websitehttp://www.ttf.co.uk/Environment/Certification.aspx.
Specifying Constructional OSB
Constructional OSB comes in four grades (technical classes) as defined in the European Standard EN 300 and shown in the table below. The standard specifies the requirements for OSB for general purposes or structural applications in dry and humid conditions. Selection of a grade of loadbearing panel is dependent upon the ambient climatic conditions together with the level of loading that is anticipated.
As with structural plywood, Structural OSB (OSB/2/3/4) has proof of strength performance provided by the supplier in addition to other product performance information.
As with plywood, OSB that is used in construction must comply (by law) with the Construction Products Directive (CPD) and the recommended way to achieve this is by compliance with the Harmonised Standard for woodbased panels (EN 13986); this standard calls up EN 300 for OSB. A 'CE' logo may be present as an indication that the OSB meets the requirements of the European Standard EN 13986.
Examples of Constructional Plywood marks
Examples of Constructional Plywood marks are given below and are used to identify certain things:
1) The End use class, for example EN 6362 for Humid Uses or EN 6363 for Exterior Uses. A 'CE' logo may be present as an indication that the plywood meets the requirements of the European Standard EN 13986.
2) If it is structural plywood there will be:
- An 'S' or the word Structural following the end use class e.g. EN 6362 S
- An identification number in the format XXXX-CPD-YYYY. Where the first number (XXXX) identifies the Notified Body which undertook independent third party assessments to allow CE Marking and the second (YYYY) identifies the Supplier.*
- The words 'FLOORING', 'ROOF' or 'WALL' to indicate suitable use(s) for the Plywood.
*NOTE: If a CE mark is affixed to the plywood it indicates that the product is making a claim that it complies with the Harmonised European Standard EN 13986. However, please note that the Attestation of Conformity Level 2+ (commonly referred to as CE2+) which tells you the level of involvement of a Notified Body is not applied to the mark as this only tells you that a mill is capable of producing structural plywood. The mark CE2+ does not in itself indicate suitability for structural use. For more information on CE Marking of panel products please click on the link below: http://www.ttf.co.uk/Document/Default.aspx?DocumentUid=CAB53189134245DF86883825976F395D
Plywood missing any or all of the factors in 2a, 2b, and 2c above should be considered as general plywood only and therefore should not be used in load bearing work such as flooring, flat roofs or wall sheathing. Responsibility for ensuring only structural plywood is used in load bearing applications rests with the contractor.
Although the mark gives vital information always look at the Product Data Sheet provided by the supplier as this will show the exact level of performance which can be expected from the plywood.
The surface appearance of plywood should not be used as an indicator of its structural performance. For example, structural plywood may not need decorative faces because it is hidden in use. General purpose plywood meanwhile may have better quality faces because it is used more decoratively and/or is painted.
Example of a structural plywood mark
Expect to see a mark on each sheet of Structural Plywood either printed vertically (as right) or horizontally (as below). Structural performance data is obtained from the product data sheet.
Example of a general plywood mark
Example of a structural OSB mark
EN 300 - 2006 Oriented strand boards (OSB). Definitions, classification and specifications
EN 636 2003 Plywood: Specifications
EN 13986 2004 Woodbased Panels for use in Construction: Characteristics, Evaluation Of Conformity And Marking