INTRODUCTION

This Digest describes the general processes that may be applied when making a structural appraisal of many types of building and structure, but there is a particular focus on the requirements associated with making a material change of use to part or all of an existing building, as defined in Part 2 of the Building Regulations 2010^[1] for England and Wales (hereafter ‘the Building Regulations').

Although Scotland and Northern Ireland are governed by separate legislation, the general objectives and requirements are similar, but there are subtle differences. For example, Scottish Building Regulation 12 concerning conversions poses more onerous requirements. The fundamental principles of structural appraisal described in this Digest, though, will be generally applicable in all three legislatures.

In the context of the Building Regulations, a structural appraisal in respect of a material change of use must assess compliance with the requirements of Part A, Structure, of Schedule 1 of the Building Regulations. The primary concerns are structural safety, strength and stability of the building under normal loads and actions (Requirements A1 and A2), as well as reducing its sensitivity to disproportionate collapse under accidental loads and actions (Requirement A3). In many ‘traditional' buildings it may be much more difficult to establish compliance with Requirement A3 than with Requirements A1 and A2. This Digest therefore focuses on this aspect of the requirements, and on the processes associated with undertaking a structural assessment for it.

Part 1 of this Digest considers the overall regulatory requirements, and in particular the disproportionate collapse issues associated with Requirement A3. It describes what constitutes a material change of use, reviews the Building Classes (see Section 5 of Approved Document A: Structure[2]), and then examines means of reducing sensitivity to disproportionate collapse in respect of Building Classes 2A, 2B and 3, as defined in Table 11 of Approved Document A. It also discusses the provisions in the structural Eurocodes for reducing sensitivity to disproportionate collapse.

It is necessary to consider the three documents together – the Building Regulations, Approved Document A and the structural Eurocodes – because although the intent of their provisions aligns, the specifics of their wording, terminology and referencing are not entirely consistent. This is because they were drafted and came into force at different times. This Digest therefore reviews the provisions of all three documents.

Part 2 of this Digest introduces structural appraisal, and discusses the factors that might influence the outcome of an appraisal, and what might be involved in preparing for it. Part 3 describes structural appraisal procedures. Part 4 provides additional information.

Because of the diversity in the nature and condition of existing buildings, the guidance given is of a general nature, intended to support the appraising engineer's own professional knowledge, experience and capabilities.