Durability

Durability is the resistance to degradation of products, materials, buildings and other built assets over time. This can be a difficult property to assess - whilst a tough material may be hard to the touch but it may also be non-durable if it decomposes or is eroded in a relatively short period of time.The opposite can also be true.

Many factors affect durability, whether concerning the nature of the material itself or the way it has been assembled with other materials:

• Molecular structure.
• Resistance to damp, moisture and water.
• Resistance to corrosive substances.
• Resistance to vermin and other aggressive animal life such as wood boring beetles.
• Resistance to mould and rot.
• Fire resistance.
• Ability to accept movement.
• Resistance to atmospheric pollution.
• Resistance to heat and cold.
• Capacity for moisture absorption.
• Surface profiles, orientation, texture and colour.

As well as its constituent materials, a building as a complete entity may also be said to be durable (or non-durable). Buildings constructed for temporary purposes, such as demountable site cabins and exhibition pavilions, do not tend to stand the test of time because they are not designed to.

A building will be subjected not only to daily wear and tear from users but also to the constant influence of climate – in particular rain, frost, sun and heat – forces collectively referred to as weathering. Such forces can cause significant deterioration and therefore a reduction in durability.

As well as diminishing durability, weathering forces can also result in a change of appearance – usually a change for the worse – however some materials can be affected beneficially: some stones and brick types for example, as well as some metals such as copper which develop a patina.

As well as causing potential staining – particularly in polluted areas – some forms of weathering e.g acid rain, result in chemical actions which can cause deterioration of the building fabric. Changes in moisture content, temperature, frost, sunlight, soil and groundwater action, atmospheric pollution and the action of electrolytes, mould and insect attack can lead to corrosion, erosion and disintegration of materials and construction details. Materials must therefore be carefully understood and specified according to their properties, their juxtaposition with other materials in the building and the potential destructive agents they may face.

Design can have a direct effect on durability: even the best materials may deteriorate prematurely if they are not adequately maintained, and a design which makes this difficult e.g timberwork that is inaccessible and so infrequently painted, will have adverse effects on component durability. Sometimes, designers must face a trade-off between the initial costs of materials and the likely future costs of maintenance and the resulting effect on durability.

Economic considerations will play a significant part in determining the durability of a construction: the best possible materials assembled in a considered, careful way tends to be the costliest method of approach yet this may frequently result in best quality and longest durability.

Durability is becoming more of a concern in relation to the likely impact of climate change, in particlular, higher temperatures, rising water levels and more frequent extreme weather events.

In some cases buildings may be designed to be deconstructed, as well as being durable, so that at the end of their lives, they can be easily recycled or re-used.

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