Types of design life

[edit] Introduction

The design life (or design service life) of a building, other structure or component, is the period of use as intended by the designer after which it may need to be replaced. Before this period has elapsed, it should remain fit for purpose. Below is a brief description of the term along with a number of other related terms.

There is no legally agreed definition of these terms, so if they are to be included in contract documentation as a performance requirement, it is important that they are carefully defined and that this is consistent with all other requirements in the contract documents.

[edit] Design life

Design life will vary according to the type and use of the element being considered. BS EN 1990, Eurocode - Basis of structural design, (Eurocode 0) gives indicative design lives for various types of structure:

• Category 1: Temporary structures, not including structures or parts of structures that can be dismantled with a view to being re-used – 10 years.
• Category 2: Replaceable structural parts, e.g. gantry girders, bearings – 10 to 25 years.
• Category 3: Agricultural and similar buildings – 15 to 30 years.
• Category 4: Building structures and other common structures – 50 years.
• Category 5: Monumental building structures, bridges and other civil engineering structures – 100 years.

The design life of some components may be affected by environmental factors such as:

• Moisture, humidity and rain.
• Wind.
• Temperature and temperature fluctuations.
• Pollution.
• Solar radiation.

It may also be affected by considerations such as maintenance practices, intensity of use, and so on.

[edit] Required life

'Required life' is the minimum period during which the element, or part of it, should meet the users’ requirements. This means that it should remain capable of performing its design functions, taking into account routine servicing and maintenance. This may be set out by clients in briefing or tender documents in order to specify how long the element should fulfil their requirements, before potentially needing to be replaced.

[edit] Technical life

Technical life refers to the actual time that the element may be in service until a defined minimum acceptable state is reached. The building owner and/or the facilities management team may be concerned with the technical life of elements, as costs and management time are likely to escalate as more maintenance issues arise beyond the expected technical life.

[edit] Functional life

Functional life refers to the amount of time that an element may be in service before it is rendered obsolete due to changes in functional requirements, such as a change in use.

[edit] Economic life

Economic life refers to the amount of time an element is in service before its replacement is more advantageous economically than the continued maintenance that will be required to keep it in service. Economic life may be a key consideration of owners, particularly if they are managing the an asset from which they wish to ensure an adequate return on the investment they have made by purchasing or building it and operating it.

[edit] Service life

The Home Quality Mark One, Technical Manual SD239, England, Scotland & Wales, published by BRE in 2018, defines ‘service life’ as: ‘The period of time after installation during which a building, or its part, meets or exceeds the performance requirements.’ Ref: BSI, BCIS. 2008. PD 156865. StandardiSed Method of Life Cycle Costing for Construction Procurement. s.l. : BSi, 2008.

Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019, defines service life as: ‘The period of time after construction or refurbishment when an asset meets or exceeds its functional performance requirements.’ It defines residual service life as: ‘Service life remaining at a certain moment of consideration (also known as residual life).’

Redefining value, The manufacturing revolution, Remanufacturing, refurbishment, repair and direct reuse in the circular economy, published by the United Nations Environment Programme in 2018, suggests service life: 'Refers to a product’s total lifetime during which it can be used economically or the time during which it is used by one owner, from
the point of sale to the point of diversion for reuse via VRPs (Value-Retention Processes), or to the point of disposal(Cooper 1994). This is differentiated from Expected Service Life as it refers to the actual service life and is not necessarily associated with manufacturer expectations or commitments.'

It suggests that expected service life: ‘Refers to the manufacturer’s expectations about the time-period for which a product can be used, usually specified as a median, and reflecting the time that the product can be expected to be serviceable and/or supported by its manufacturer.’

Full service life: ‘Refers to value-retention processes (VRPs) that enable the fulfillment of a complete new life for every usage cycle of the product, and includes manufacturing (OEM Original Equipment Manufacturer new), comprehensive refurbishment, and remanufacturing. These processes take place within factory settings and industrial operations.’

And that partial service life: 'Refers to value-retention processes (VRPs) that enable the completion of, and/or slight extension of, the expected product life, through arranging direct reuse of the product, repair, and refurbishment. These processes take place within maintenance or intermediate maintenance operations.'

See also: Service life of products.

[edit] Related articles on Designing Buildings

• Challenging the current approach to end of life of buildings using a life cycle assessment (LCA) approach.
• Circular economy.
• Cradle-to-grave.
• Design economics.
• Design for Deconstruction.
• Design life.
• Doughnut economics.
• End of life potential.
• Life cycle assessment.
• Life cycle inventory.
• Life-cycle plan.
• Life cycle in the built environment.
• Re-evaluating the design life of buildings.
• Reference service life.
• Required life.
• Service life of products.
• Technical life.
• The Value Toolkit.
• Useful life.
• Utilising life cycle costing and life cycle assessment.
• Whole life costs.
• Whole life solution
• Why we need to grasp the whole life cycle.

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