Design life

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.

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.

There is no legally agreed definition of design life (in fact, there is not even a legally agreed definition of 'design'), so if it is to be included in contract documentation as a performance requirement, it is important that it is carefully defined within the contract documents and that it is consistent with all other requirements in the contract documents.

Several other definitions have been developed to quantify the life of buildings, structures and their components, including: