Sources of moisture

Serious damage can be caused by floods, even though it is not listed as a primary 'source' of moisture. Flooding ranges from internal localised flooding – from burst pipework, for example – to the kind of widespread and serious flooding in risk areas where properties built on 'flood plains' are under threat of natural flood damage every winter.

Problems of flooding from poor drainage have appeared more frequently in the national press. In some areas there is a threat to homes from sewage water, where foul drainage systems are unable to cope with the sheer volume of discharge during heavy and persistent rain.

Surveyors can obtain a flood report from the National Rivers Authority and from the Environment Agency; their website contains maps of flood plains and other useful information. Other more general websites on UK property by postcode also usually include a section on flood risk.

The RICS Residential Property Professional Group's 'Flooding and Coastal Erosion Group' produces information concerning flood risk to property, and the risks inherent in surveying properties that are prone to flooding. A checklist produced by the group focuses mainly on 'external factors' that should be evaluated when carrying out a building survey or a valuation. Such factors include geographical and geological patterns of the locality – for example, changes in farming practice that could affect land drainage.

Areas also vulnerable to flooding are where de-industrialisation has occurred on a major scale, e.g. closure of mining areas. However, as we have witnessed globally, weather systems involving unusually high rainfall intensity over prolonged periods along with the confluence of seasonal high tides have wreaked havoc on major areas. Year on year there is a major episode of flooding somewhere in the world and with increasing regularity closer to home in the UK.

The writer was involved in investigating buildings during and after the first of the major floods in Carlisle in 2005 and, despite a massive government funded dewatering scheme being introduced at a cost in excess of £38 million, Carlisle has continued to flood. Despite the best endeavours of a team of advisors in predicting the worst case for flooding for Carlisle, along came another major weather system which exceeded the severest of predictions and models previously understood.

Calls for engineers and architects to come up with more innovative designs that can cope with areas known to be vulnerable to flooding is one of the new and major challenges in the built environment. However, Carlisle, like so many towns and cities across the UK, has an ageing property stock and therefore would rely on the implementation of district or regional flood defences, rather than any significant improvements to individual homes.

One of the major findings by the writer from the Carlisle floods was the mixed methodologies of measurement in determining whether buildings are fully dried out. Many were found to exhibit ongoing dampness that eventually was found to have resulted from pre-existing defects on the building unrelated to the flooding.

Venice copes with an average annual flood rate of about 80 separate flood events annually, yet life goes on despite these occurrences, although at the expense of many buildings not being occupied at ground floor level. The ground floors have become the sacrificial storm drain. Preventative infrastructure schemes such as the Moses project, which is a raisable barrier within the Venice lagoon, can prevent a bow wave of just over 2 meters. Venetians hardly need to be reminded of one of the worst floods in their history, when in 1966 a Tsunami wave in excess of 2 meters engulfed Venice, having a devastating effect on the buildings and a major threat to the Venetian way of life.

Flood defences need to be constantly kept under review and regularly maintained, so that they work when actually required.

Despite climate change summits and the introduction of cutting carbon footprints by governments across the globe (in the UK the Climate change Act), the race to find alternative clean energy has begun and must succeed if we are to halt or even reverse the effects of increasingly severe and unpredictable weather patterns across the globe. This is the ultimate challenge to flood defences.

Local water tables are also increasing in height as a result of over-development and redevelopment of urban areas on brownfield and greenfield sites, new town creation and new infrastructure. In some development areas, counter measures include the provision of water pumping substations to manage fluctuating rises in water tables (created by the displacement of ground water that the additional buildings have caused).

Local people usually know of any history of flooding in the area, even if the parties selling a property are somewhat evasive. There is a legal duty for sellers to reveal all they know about flooding to the house and site they own when they are asked questions by the prospective purchaser.

Contamination by river water or sea water poses a health risk. If a property has flooded prior to survey, there are a number of symptoms of past flooding that surveyors need to be aware of.