Printed from the ArchiMentor Knowledge pages on - www.archimentor.net

Design Life

• Introduction
• Standards
• Good practice
• Guidance

Introduction

• The subject of Design Life deserves much wider discussion, and at a much earlier stage, than has ever been typical practice in the UK construction industry.
• Just as the PFI initiative was beginning to re-awaken interest in the related issue of life cycle costing, the issue became confused by the publication of the 2003 edition of BS 7543.

Standards

• For many years the only relevant British Standard was BS 7543 : 1992 "Guide to durability of buildings and building elements, products and components".
• An International Standard, ISO 15686, was published in 2000 and this replaced many, but not all, of the provisions of BS 7543 : 1992. The ISO standard is in a number of parts, most of which are pretty impenetrable and of little direct relevance to specifying architects.
• BS 7543 : 2003 is the 'rump' of what is left from the 1992 edition after extracting items covered by ISO 15686.
• The current situation is generally agreed to be unsatisfactory and BSI are understood to be considering another revision to BS 7543.
• Current definitions:
  Service Life (BS ISO 15686-1, clause 3.1.1.): Period of time after installation during which a building or its parts meets or exceeds the performance requirements.
  Design Life (BS ISO 15686-1, clause 3.1.4.): Service life intended by the designer.

Good practice

Concept, Scheme, and Detail Design Stages

• It is a good idea to discuss the design life of the building, and its components, with the client as early as possible and to ensure that the results of such discussions are properly recorded.
• The Guidance below may be used as a starting point for these discussions.

Production Information Stage

• Prescriptive Specifications. It is usually unnecessary to state the design life. The assumption should be that the specifier has selected materials and methods of construction which have the design life agreed with the client. Specifying the design life is contractually irrelevant and may lead to misunderstanding.
• Performance Specifications. It is always necessary to state the design life as this is one of the crucial "performance criteria" that must be specified.
• Specifications for Design and Build Contracts. It is always necessary to state the design life as this is one of the aspects of the design for which the contractor is taking responsibility. This applies equally to those items of the works which would be specified prescriptively for contracts which are not Design and Build.

Guidance

• BS ISO 15686-1, clause 6.8.1, Table 1 provides "suggested minimum design lives for components" based on the design life of the building and organised into four categories:
  - Inaccessible or structural components.
  - Components where replacement is expensive or difficult.
  - Major replaceable components.
  - Building services.
• We have introduced a fifth category - Other replaceable components - to cover other components for which specifying the design life might be desirable.
• The suggested minimum design lives for components, shown below, are based on a building with a 60 year design life as 60 years was described as 'Normal Life' in BS 7543:1992, Table 1 (now withdrawn). This is a generally-accepted standard for high-quality office buildings in the UK but the period should be reviewed for other building types.
• Note that the 30 year design life to be specified for "Major replaceable components" is less than the 40 years suggested in BS ISO 15686-1, Table 1, on the basis that components should be replaced a finite number of times within a building's design life, e.g. 2x30=60, 3x20=60, etc.
• You should dicuss the 20/15 year options for "Other replaceable components" with the client as, contrary to what may seem obvious, higher-quality commercial buildings may justify a shorter design life on the assumption of regular internal re-fits. The difference between 15 and 20 years is, however, probably academic for these items, with the exception of the door furniture.

Inaccessible or structural components - 60 years

• Structural steel framing.
• Brickwork and blockwork.

Components where replacement is expensive or difficult - 60 years

• Concealed wall ties, wind posts, and similar accessories for masonry walling.
• Secondary structural steelwork.
• Stairs/walkways/balustrades (Stair structure).
• Basement waterproofing.
• Fire protection and fire stopping.

Major replaceable components - 30 years

• Curtain walling.
• Structural glass assemblies.
• Metal profiled/flat sheet cladding/etc.
• Precast concrete panel cladding/features.
• Metal composite panel cladding/covering.
• Natural stone slab cladding/features.
• Rainscreen cladding.
• Windows/rooflights/screens/louvres.
• Stairs/walkways/balustrades (Balustrades).
• Fixed utilitarian access systems.
• Permanent access and safety equipment.
• Roof finishes.
• Raised access floors.
• Floor screeds.

Other replaceable components - 15/20 years

• Plasterboard dry linings/partitions/ceilings.
• Demountable suspended ceilings.
• Doors/shutters/hatches.
• Internal and external floor and wall finishes.
• Sanitary appliances.

© 2008. ArchiMentor.