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Common defects in Modern Buildings

01/07/2015

Modern construction is increasingly a process of assembly. Whilst this inevitably removes some of the risks inherent in building, it also creates a series of new problems, most particularly with coordination and interfacing.

As design methodology improves and performance standards become more exacting, buildings are also becoming more finely engineered. This also brings potential issues as more finely you engineer a structure, the more the physics of a building become critical.

Whilst older, heavyweight buildings were often thermally inefficient, many were robust in construction and able to cope with the extremes of weather and with the changing demands of future generations - changes of use from office to hotel or residential, residential to office or leisure use etc. Today’s lightweight construction is prone to movement and may not be so well with extreme weather, user abuse or changing requirements.

We should not fall into the trap of assuming ‘modern’ equals ‘bad’ as generally only ‘good’ older building survive and there will, no doubt be examples of buildings constructed in the last 10 years that will still exist in 100 years’ time. The challenge, as technology brings about new methods and forms of construction is how to assess the likely performance of these and how to balance innovation and realism.

Over the last year or so I’ve been involved with a number of building failures in modern buildings, nearly all of them foreseeable given past experience. Not one of the failures was genuinely “new”, all were due to a failure somewhere along the line to recognise and apply a few essential principles. I’m not saying that defects and failures can be eliminated entirely; however I do think that more attention to coordination and interfacing between different materials and products as well as a basic appreciation of some basic scientific principles will serve to improve matters.

For example, we know that most things conform pretty much to the following:

Gravity will cause things to move from high to low; for example water working its way down a building will do so via gravity therefore follow the likely path to the point of ingress.

Temperature will flow from high to low and vice versa. Think about the effects of cold bridges, the correct location of insulation, the risk of heat loss and so on.

Vapour Pressure. Water vapour in a high pressure area will gradually leak or diffuse to an area of low pressure. For example moist air (high vapour pressure) will move towards an area of dryer air (low vapour pressure) creating condensation risks.

Air Pressure will flow from an area of high pressure to an area of low pressure. Air movements through a glazing system are often one of the biggest sources of leakage. Prevent the transfer of air pressure and so prevent leakage.

Corrosion. Other than gold, most metals in buildings require large amounts of energy to transform them to a processed state. The resulting products are metastable and with environmental influence gradually revert back to their unprocessed state – the process of corrosion; in effect a transfer of energy from high to low.
Remember also that materials and products have different lives; they may co-exist but:

  • They have different ranges of thermal movement;
  • They have different levels of durability;
  • They can be incompatible with one another and;
  • They need to be assembled – you cannot treat one thing in isolation from another.

Objectives. Aim for balance with the surroundings and for between parts and the whole. For example equalising pressure behind a rainscreen will limit air movement and prevent or reduce water transfer. Aim for continuity of structure, thermal performance, sound and fire protection; provide discontinuity where appropriate for example cavity breaks, damp proof courses.

Many of the defects I see in the course of my work could have been avoided if one or more of these had been applied. Examples such as not installing adequate sub-floor ventilation, incorrect specification and/or construction sequencing, lack of consideration of materials interfaces and, perhaps most surprisingly, no consideration on the effects of gravity on suspended  ceilings, are all relatively straightforward and demonstrate either a lack of knowledge or a failure to apply basic principles – or both?

Sometimes, failures can be a little more obscure, albeit not necessarily new. Take the recent media attention given to failing bolts at the ‘Cheesegrater’ development in London. The failures here were reportedly due to a process known as hydrogen embrittlement whereby hydrogen atoms are able to penetrate the surface of high grade steel and become trapped by the subsequent plating or finishing process. The hydrogen can then migrate to regions of high stress causing sudden and unplanned failure. Whilst this process may be unfamiliar to many, it is, in fact, a principle that has been known about for some 140 years or more.

As a Building Surveyor I have the advantage of hindsight gained from picking over the wreckage of failure. I would like to say that the benefits of hindsight will gradually filter through the industry, but the reality is that without a hefty dose of common sense and an appreciation of the basic principles, failures will continue to occur. 

For more information contact trevor.rushton@watts.co.uk

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