Fighting Floods and Overcoming Overheating by Mark Oliver
Hardly a day has gone by this year without flood warnings, flood risks and flood management being mentioned in the media. The Environment Agency has already issued hundreds of flood warning and alerts for England and Wales this year and in Scotland, the Scottish Environment Protection Agency has issued 27 flood alerts and 61 flood warnings between January 1st and January 20th alone. The Environment Agency estimate that already this year around 640 properties have flooded in England alone.
The cause of the extreme weather conditions that the UK has witnessed in recent years is a subject of growing debate. in early January the Prime Minister told MPs: "We are seeing more abnormal weather events. Colleagues accross the House can argue about whether that is linked to climate change or not. I very much suspect it is." Climate change experts are, in general, wary of linking specific weather events to climate change. Dan Williams from the Met Office said: "You can't make a definitive statement about how more or less likely the recent flooding has become because of climate change." However, numerous academic studies have suggested that there is a relationship between climate change and increased occurrences of flooding as well as more frequent heat waves.
In 2008 the Environment Agency's National Flood and Risk Assessment indicated that there are 2.4 million properties at risk of flooding from rivers and the sea in England, with a further 2.8 million susceptible to surface water flooding alone.This equates to one in six properties being at risk of flooding. If the scientists are to be believed then the probability of flooding in the UK is going to continue to increase rather than diminish in the coming years and decades which is, and will continue to be a problem, for current and future home owners across the country.
Fighting the Floods
Smaller building firms always look for advice and support from their merchants, therefore it is important that regardless of the size of your company you are able to confidently assist your customers.
Guidance on flood resilient constructions was last given by the Department of Communities and Local Government in 2007 in its ‘Improving the Flood Performance of New Dwellings – Flood Resilient Construction’ document. Advice is based on two strategies: water exclusion and water entry.
In a water exclusion strategy the emphasis is placed on minimising water entry whilst maintaining structural integrity and using materials and construction techniques to facilitate drying and cleaning. This strategy is favoured when low flood water depths are involved, up to a maximum of 0.6 metres. In a water entry strategy emphasis is placed on allowing water into the building, facilitating drainage and consequent drying. This strategy is favoured when high flood water depths are involved: greater than 0.6 metres.
Regardless of what water strategy is implemented when building a new home, the principle material used in construction is vitally important. For both strategies masonry is the preferred building material as it is not made from materials that have the potential to rot and loose performance when wet. The type of mortar utilised in masonry constructions can also help with keeping water out of a property. The DCLG’s document says: “there is evidence that thin layer mortar construction is a good flood resilience option”; this is more commonly referred to as the thin-joint method of building.
For a home built using a water exclusion strategy the expected amount of leakage into the fabric of the building is minimal. Because of this the DCLG recommend the use of aircrete blocks. Although they may retain moisture for longer than traditional mortar, they allow less leakage.
Flooding is not the only extreme weather phenomenon that the country has witnessed in recent years. The Grantham Research Institute on Climate Change and the Environment predicts that the UK could experience warmer, drier summers in the future but points out that while this ‘may bring some benefits, it could mean increased risk of drought, and extreme events, such as the 2003 heat wave, could be the norm by the end of this century.’ Since the 1970s temperatures in the UK have risen by circa one degree and some scientists believe that further warming is inevitable in coming decades.
The construction industry needs to adapt its buildings to ensure that people can live, work and play in comfort as temperatures and water levels rise while still ensuring that carbon levels are kept to a minimum. Both the Department for Communities and Local Government and the NHBC Foundation have produced reports on overheating in dwellings and the consequences for the health of occupants.
According to NHBC Foundation ‘there is increased evidence that new and refurbished properties are at risk of overheating’ and that some temperatures currently being reached in existing dwellings are harmful to the health and well-being of occupants. This is especially prevalent in small properties and flats where cross ventilation is not possible. This issue is compounded by increasingly stringent Building Regulations set out under Part L as prototype, zero-carbon, houses have been found to suffer from overheating. This indicates that overheating may also be an issue where cross ventilation is not attainable in lightweight, airtight houses with limited ventilation.
There are certain design elements that can be introduced to mitigate the effects of overheating and future proof a dwelling such as shading, blinds and night time purge ventilation which lets hot air out of the building and cold air in.
One element of house building that is underestimated when it comes to overcoming the effects of overheating is the material used to construct the building. Certain materials such as masonry help to counteract the problems of overheating. The thermal mass characteristic of the blocks enables them to extract heat from the building during the day and put it back in at night when it is cooler. In hotter climates builders are recommended to use the effects of thermal mass where possible to make buildings more comfortable. The use of materials with high thermal mass properties mitigates the need for increased ventilation which is often needed in lightweight frame structures because heat can get in but it is difficult for it to escape.
Aircrete for example, is used around the globe because of its high thermal mass properties. It was initially used in Scandinavia for its insulating properties to counteract the cold but it is also used in warmer climates such as India for the opposite purpose. It cools down the buildings and reduces the load on air-conditioning units.
Looking to the Future
In April this year the new Approved Document L will come into effect. It primarily focuses on limiting the amount of CO2 emitted from houses and ensuring that properties have strict levels of air-tightness but there is also recognition of overheating in the summer. If a builder follows the general recommendations set out in the new regulations, occupants should still find their home pleasant to live in but overheating is something that will need to be taken into consideration at a greater level when Part L is next amended. The higher the levels of air tightness the greater the chance of overheating especially if a light weight structure is used. As a country we tend to wish for hotter summers and drier winters. But it seems as though we are going to be getting hotter summers with wetter winters, possibly also wetter summers. Even the most sophisticated technology struggles to accurately predict the long term weather forecast but what is certain is that the weather in the UK is changing and we are subject to more and more outbreaks of freak weather. As an industry we need to ensure the buildings we are building now will cope with whatever the weather throws at them in years to come.