Defects: modern buildings
4 September 2015
Defects in modern buildings are due to a failure to apply a few essential principles, argues Trevor Rushton
The past 25 years or so have seen massive changes in construction practice and materials. While craft skills still exist, modern building is a process of assembly; this may remove some of the inherent risks, but it also creates a whole new raft of problems with coordination and interfacing.
In tandem, changes in materials, improvements in design methodology and exacting performance standards mean that buildings are becoming more finely engineered. But beware, the more finely engineered a structure, the smaller the margin for error.
Older, heavyweight buildings were often thermally inefficient but many were robustly constructed and able to cope with both the extremes of weather and changing user demands; from office to hotel or residential, residential to office or leisure use, etc. Today's lightweight construction is prone to movement and may not cope so well.
More attention needs to be paid to basic performance constraints as well as coordination and the interface between different products
It is easy to be critical of modern construction and suspicious of new materials. But remember, we only see surviving examples of 'good' older buildings; the poor ones have already been consigned to the scrapheap. No doubt many good contemporary buildings will still exist in 100 years or so.
For building surveyors faced with unfamiliar methods and forms of construction, the question is how to assess their likely future performance. Will they continue to meet expectation or will they cost a fortune to repair and maintain? We certainly do not want to stifle innovation in favour of the tried and tested, but at the same time we need to be constructively pessimistic.
Over the past year or so I have been involved with a number of building failures in modern buildings; all due to a failure to recognise and apply a few essential principles. I am not saying that defects can be eliminated entirely; part of the process of getting things right is in first getting them wrong. However, more attention needs to be paid to basic performance constraints as well as coordination and the interface between different products.
In his book, Building failures: a guide to diagnosis remedy and prevention, Lyle Addleson summarises some principles that are worth remembering. For example, we know that most things conform more or less to the following basic constraints:
- Gravity: will cause things to move from high to low; for example, water working its way down a building will follow the likely path to the point of ingress.
- Temperature: will flow from high to low and vice versa. Think 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 will move towards an area of dryer air 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 one of the biggest sources of leakage.
- Corrosion: other than gold, most metals 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.
- Differences: materials and products may co-exist but have different ranges of thermal movement and different levels of durability. They can be incompatible and need to be assembled – you cannot treat one thing in isolation from another.
- Control: Anderson also recommends making an allowance for uncertainty on the basis that the performance of materials and the way in which they are used is not always predictable.
I have the advantage of being able to pick over the wreckage of failure, and learning from the mistakes of others is easy. The hard part is avoiding the mistakes yourself. Remember the basic principles and they will serve you well.
Trevor Rushton is Technical Director at Watts Group
Related competencies include:
This article is taken from the RICS Building Surveying Journal (July/August 2015)