BS 5268-2 : 2002 Structural use of timber – Code of practice for permissible stress design, materials and workmanship

Code revised, 2002

Why BS 5268: Part 2 is important

• A plywood panel manufactured with exterior glue does not automatically allow it to be used in a load bearing application.
• Other criteria such as design values have to be considered and these design values involve compliance with BS 5268-2 or Eurocode 5.
• BS 5268 is the controlling document clearly listed in the Building Regulations.
• It is referenced by the NHBC; and the National Building Specification issued by the Royal Institute of British Architects.
• It provides guidance on the structural use of timber, glued laminated timber, plywood and other panel products in load-bearing applications.
• The revised code includes recommendations on quality, grade stresses and modification factors for materials used in structural applications.
• By reducing the number of material specifications, the revised code has also eliminated related supplier problems.

Now running parallel with Euro Code 5

• The revised code incorporates most of the CEN material standards specified in Eurocode 5 - and will run parallel to it, until the Eurocode finally replaces BS 5268: Part 2 around 2008.

Benefits of harmony with Eurocode 5

• Updated range of imported plywood permitted for structural loading.
• Replacement of two service exposure conditions (dry and wet) with three service classes (dry, humid and exterior).
• Guidelines for deriving grade stresses and moduli for certain types of plywood.
• Allows for compliance with EN 13986, the harmonised European standard covering the use of wood based panels in construction. This involves third party auditing of factory production control by a European Notified Body. In addition, the mechanical properties of the plywood have to be determined by a European test - EN 789, see below.
  

Section 4.1 Plywood – General

• Increases the plywood types acceptable for structural applications in the UK.
• Details the use of plywood manufactured in accordance with the foreign standards listed in Section 1.5 – Materials …and subject to the quality control procedures of specifically named bodies.
• For US plywood, the only two quality auditing bodies named are:
  - APA – The Engineered Wood Association
  - TECO Corporation

[Section 1.5 (d) lists American Product Standard PS1-95 American Construction and Industrial Plywood as the controlling document for the manufacture of American structural plywood bearing the trademarks of APA – The Engineered Wood Association (APA), or Teco Corporation (TECO)].

• New clauses appearing in Section 4.1 also permit the use of US plywood manufactured to the American Product Standard PS2-92, Performance Standard for Wood-based Structural Use Panels; and PRP-108, Performance Standards and Policies for Structural-Use Panels. These panels satisfy the requirements for the method of determining the grade stresses and moduli as laid down in the last paragraph of BS 5268-2 Section 4.1 and in Section 4.6.

Section 4.6 – Design data derived from characteristic values

• Sub-clause (c) requires that characteristic values for plywood must have been derived in accordance with BS EN 789 and BS EN 1058 for plywood conforming to the appropriate sections of BS EN 636-1, -2 or –3 (i.e. Section 4.4.2 – Structural application).
• These characteristic values must be converted by the given formulae for use in design based on permissible stress.

As at April 2003, only American plywood, trademark stamped by the APA fulfils this requirement.

Section 4.8 – Plywood for roof and floor decking

• The design of plywood for decking on roofs and floors should be determined:
  by calculation using grade stresses and moduli.
• This permits the use of American PS1-95, PS2-92 and PRP-108 plywood.