Introduction

This sample specification should be beneficial for everyday timber specification and general Bill of Quantities use. It indicates the essential timber specification elements but could be supplemented with additional clauses from the Building Specifications (Section D) where appropriate.

BS 5268 Part 2 is the main design standard currently used in Ireland and the UK. The equivalent European standard is Eurocode 5 (formally designated EN 1991-1-1 and EN 1995-1-2). The convention is adopted that italics are used in specifications where a specific material or dimension is specified which may be altered at the discretion of the specifier (as long as it complies with good practice or the appropriate standards).

USE OF STANDARDS

In presenting broad-based specifications considerable reference has to be made to appropriate standards. At present there is continuing harmonisation of standards within the European Union, and European standards, known as Euro Norms (EN), are being adopted by member states which supersede the national standards. It is very important to check that quoted standards are current, as it is quite conceivable that certain national standards may no longer apply, or European standards may already be undergoing revision.

It is important to note that, whereas both standards may be acceptable, they may not be interchangeable as parameters within the standards may differ. Where IS444 (or BS 5268) and Eurocode 5 are quoted they are mutually exclusive and either the IS/BS or Eurocode 5 may be used but not both. Generally the design and loading codes or standards (e.g. the wind codes) are separate and incompatible (with some exceptions). It is far safer to use ENs with EC 5 and IS/BSs with IS444/BS 5268. However, some product EN standards are applicable to the IS or BS (e.g. the plywood standard EN 636 and the standard on timber tolerances EN 336). The mixing of standards must be undertaken with care and generally the only mixing is within the product standards.

All Euro Norms are quoted as EN followed by the appropriate number. These ENs should be adopted by member states, in which case they may receive a further designation denoting their acceptance as a standard by a particular country. For example, when adopted by Ireland an EN will become IS EN; similarly an EN adopted by Britain becomes BS EN. Because of the rate of promulgation of ENs, the process of adoption is ongoing. Therefore this Guide does not show the national prefix. See section E4.

Alternative standards are quoted in certain circumstances and it is important to ensure that these standards are concurrent and appropriate to the work in hand.

The main examples shown in this document are based on Irish and British Standards and in particular BS 5268 Part 2; for example the nail and screw centres and edge distances come from BS 5268 Part 2. In many cases Eurocode 5 (all of its parts) has very similar approaches to design as the different parts of BS 5268 (including designing for fire) and many of the example specification clauses here have an exact equivalent in the Eurocode.