Flood resilient buildings

FloodingThe recent flood events in Pakistan have highlighted the destruction that floods can cause. The following extract is from a BBC news report and gives an indication of the scale of the destruction caused: “Over half-a-million people have been ordered to evacuate their homes in Pakistan’s southern province of Sindh. Three more towns are now threatened by floodwaters, and there is concern about the fate of Pakistan’s sixth largest city – Hyderabad. From the air, the threat to Hyderabad is clear. A flood defence system called the Kotri Barrage stands between the city and disaster. The Indus River has swollen to 10 times its normal size here. If the water breaks through, about two million people are at risk. But the barrage is holding – for now.”

Managing flood risk

Over the years, flooding and flood risk management have become increasingly important issues. The impacts of severe events will be felt by an increasing number of the population and therefore the cost of associated damage increases dramatically. The cost of flooding cannot only be measured in monetary terms as the human costs are often impossible to calculate. Between 2000 and 2004, floods killed 185 people within the EU and affected
half a million.

In the United Kingdom such a scale and severity of flooding has been relatively rare, but it is still is the most significant natural catastrophe for the built environment and citizens. The floods that affected Cumbria in late 2009 disrupted infrastructure and caused damage to buildings and property. However, it is not only such large scale events, but also smaller scale urban flooding and flash floods that cause disruption and damage.

Climate change will exacerbate the problems of flooding and result in more frequent occurrences with greater life and property losses being experienced. If this wasn’t enough then increasing urbanisation, the creation of more hard surfaced areas, antiquated sewer infrastructure and coastal erosion are all increasing the problems of floods.

Lessons learned
The Pitt Report (June 2008) highlights the lessons learned from the summer 2007 floods and the need to develop guidance and build capacity in the stakeholders involved. Pitt recommended that building regulations be developed for new and existing buildings relevant to flood resilience. Although further research is required in this area, there is also a need for more proactive voluntary developments.

The planning legislative framework under which various agencies in the UK involved in urban flood risk management operates is complex. Separate pieces of legislation govern the activities of the environment agencies, sewage undertakers, planners and the construction industry responsible for resilience measures. Development control and planning policy is fundamental to flood risk management and the government has sought to strengthen planning guidance on flood risk in Planning Policy Statement 25 (PPS25) for England & Wales and Planning Policy Guidance 7 for Scotland and its accompanying good practice guide. PPS25 promotes a strategic approach, ensuring that flood risk is considered at all stages of the planning process and strengthening the importance of flood risk assessments in supporting that analysis.

Historically, flood risk management has mainly concentrated on river and coastal flooding. Pluvial flooding is primarily the result of run-off exceeding the drainage capacity during short, intense periods of heavy rainfall, typically summer thunderstorms. Estimates suggest that around 40 per cent of flood damage, and associated economic losses, are attributable to pluvial flooding.

Efficient procedures

There have been a number of publications produced with regard to the repair of buildings post flooding such as the British Research Establishment’s ‘Repairing flooded buildings’ (BRE, 2006) and CIRIA’s ‘Standard for the repair of buildings following flooding’ which have helped to raise awareness of key issues involved with flooding and to suggest and encourage best practice.

However, with regard to the reinstatement of flood damaged properties, current practice appears to be less effective than it could be. Major flood events have revealed that the general standard of repair is not satisfactory and although guidance for reinstating flood damaged properties has been published, including the development of new benchmark standards, there remains some doubt as to what lessons have been learned from these previous major inundations.

Flood water will cause damage to buildings and building materials in a variety of ways, as follows:
• Direct deterioration of building materials susceptible to water.
• Longer term deterioration or effects due to higher levels of moisture than acceptable for durability.
• Secondary deterioration due to freeze thaw damage or efflorescence.
• Physical damage caused by weight of water or flowing water.
As well as physical damage there is potential contamination from sewage, fuels, chemicals and other matter, as well as silts and muds that can cause damage.

Advice for developers

In 2007 the government produced guidance for development of new buildings in flood risk areas. The aim of the guidance was to provide advice to developers and designers on how to improve the resilience of new properties in low or residual flood risk areas by the use of suitable materials and construction details. These approaches are appropriate for areas where the probability of flooding is low (e.g. flood zone 1 as defined by PPS 25) or areas where flood risk management or mitigation measures have been put in place. Specifically the guidance document provides the following:
• practical and easy-to-use guidance on the design and specification of new buildings (primarily housing) in low or residual flood risk areas in order to reduce the impacts of flooding
• recommendations for the construction of flood resistant and resilient buildings.

Government policies in the UK do not advocate the building of dwellings in areas with a significant risk of flooding. However, where development is, exceptionally, necessary in such areas, national flood risk management policy requires that such developments are safe, do not increase flood risk elsewhere and, where possible, reduce flood risk overall. It is critical that new buildings in these areas are designed appropriately to cope with floodwaters and minimise the time for re-occupation after a flooding event. Time to reoccupy properties is a principal consequence of flooding which can have a profound impact on the health and livelihoods of those affected.

A major challenge to the government, local authorities and developers is to achieve a healthy balance between proper management of flood risk, whilst still ensuring that economic development and social cohesion can occur in areas at flood risk. Research is required to support government policy in this area.

Helping handbook
Recent research at BRE has addressed sustainable development in flood risk areas, the LifE Project. The LifE project resulted in a handbook that aims to help manage and reduce unacceptable levels of flood risk by raising awareness and aiding delivery of more sustainable development. It is intended to be used by decision makers, designers and developers before and during the early stages of design. The general principles of the approach can be used on all sites, but three illustrated examples and case studies focus on sites near rivers and coasts.

BRE is also coordinating a major international project on the protection of the built environment from flooding. It seeks to develop and test innovative flood resilience products for developments. The project will result in new approaches to the use of flood protection products which have become more common in the UK in recent years.

Training and education of professionals in the built environment and the flood risk area is also vital. It is necessary to translate recent research into the context of current policy and practice for professionals. As such BRE has developed a two day course in order to guide delegates through legislation, planning requirements, building standards, new build issues and repair of existing buildings to increase resilience. The course includes interactive presentation sessions and group working through set exercises. At the end of the course delegates will be able to identify the key issues, have knowledge of planning and building standards requirements for flood resilience, be able to articulate the main issues regarding new buildings and existing buildings and have awareness of
emerging issues.

Communities and Local Government (2006) ‘Planning Policy Statement 25: Development and Flood Risk’, DCLG: London.
Communities and Local Government (2007) Flood Resilient Construction, DCLG, London.
Scottish Executive (2004) ‘Scottish Planning Policy 7 (SPP7): Planning and Flooding’, Development Department, Scottish Executive.
Scottish Executive (2006) ‘Planning Advice Note 79 (PAN79): Water and Drainage’, Development Department, Scottish Executive.
BRE (2009) The LifE handbook - Long-term initiatives for flood-risk environments. BRE and Baca Architects, BRE Press, Watford.
BRE (2006) Repairing flooded buildings: an insurance industry guide to investigation and repair of flood damage to housing and small businesses, BRE Press.

For more information
Tel: 01923 664829
E-mail: train@bre.co.uk
Web: www.bre.co.uk/training