Climate change adaptation in buildings: Drought

This is the seventh in an eight-part series of articles, Climate Change Adaptation in Buildings,  examining the impact of climate change on the built environment, and the responses that can be made to those changes for both new-build and retro-fitting.

Previous articles have covered an overview of the issues, excess heat, flooding and subsidence. The final article will look at wind.

With the prediction that the frequency of weather extremes is likely to increase due to climate change, so it is forecast that periods of exceptionally low precipitation could also occur. However, these are not necessarily exclusive to the summer time; indeed, winter droughts can also occur.

Background

Perhaps the most synonymous with rising temperatures, droughts are not a new phenomenon by any means (1976, for example), but with the prediction that the frequency of weather extremes is likely to increase due to climate change, so it is forecast that periods of exceptionally low precipitation could also occur. However, these are not necessarily exclusive to the summer time; indeed, winter droughts can also occur. Falling ground water table levels can lead not only to soil shrinkage and subsidence, as discussed above, but also to depleted supplies of potable water in reservoirs. As households become progressively more affluent, and as population levels increase, so to the demand on the country’s water resources rises. Hosepipe bans are imposed by the water supply companies, and irrigation of food crops becomes the priority over motor vehicle cleanliness. Besides domestic and agricultural users, other major abstractors of water include power stations and fish farms. Not only do droughts impose physical constraints, but economic impacts are also felt.

Issues

Erosion, soil shrinkage and subsidence have been discussed already, and so the focus of this section is on water supply shortages. Although shortages can be attributable to demand exceeding supply, other factors too can contribute to those shortages. Even when it rains, either high-intensity rainfall or impermeable surfaces can result in too much rain running off into the sewerage system and being lost, with not enough percolating down in to the ground water table. Furthermore, leakages in water supply infrastructure currently account for on average 22% of public water supply per year¹. However, notwithstanding these issues, it is the demand which needs to be reduced as a priority.

Solutions

A number of initiatives have been developed over the past few years. BREEAM and the Code for Sustainable Homes (and its predecessor, Ecohomes) offer credits for the specification of water-saving measures in new buildings. The Code for Sustainable Homes’ ‘Category 2: Water’ offers credits for the following:

• Wat 1 Indoor Water Use (credits awarded for consumption of 80-120 litres per day). Current average consumption in the UK is around 145 litres per day, with regional averages of 110–185 litres per day²
• Wat 2 External Water Use for rainwater collection systems (for use in WCs or washing machines, as well as garden irrigation). Rainwater collection butts (100 litres minimum capacity for a terrace or patio; 150 litres minimum for a one- or two-bedroom house; 200 litres minimum for three or more bedrooms). These figures may be halved if there is no soft ground in the garden. For larger developments, a figure of 1 litre/m² for communal garden (or maximum 30 litres per dwelling if the development contains six or more houses) may be used. Systems should be specified to BS 8515:2009 Rainwater harvesting systems. Code of practice³. Centralised rainwater collection systems can be used for larger developments.

Similarly, BREEAM non-domestic 2011 category ‘Water’ offers credits for:

• Wat 01 Water consumption – for a percentage improvement over a calculated baseline performance. This applies to the specification of water-efficient WCs, urinals, taps, showers, baths, dishwashers and washing machines
• Wat 02 Water monitoring – for the use of water meters
• Wat 03 Water leak detection and prevention systems – prevention systems incorporate auto-shut off control devices
• Wat 04 Water efficient equipment – for irrigation or vehicle wash systems.

Grey water recycling systems, which collect waste water from showers, baths and wash basins for use in WCs and/ or washing machines, should comply with BS 8525-1:2010 Greywater systems. Code of practice⁴ and BS 8525-2:2011 Greywater systems. Domestic greywater treatment equipment. requirements and test methods⁵.

Water usage efficiency of appliances can be achieved by fitting delayed inlet valves (which prevent for example a WC cistern from being topped up before it has finished emptying during a flush, in order to enable precise control of the quantity of water being flushed, independent of the water pressure); low-flow taps, low-flow showers, low-flush and dual-flush WCs (specified to BS EN 997:2012 WC pans and WC suites with integral trap for class 2 WC suites⁶, and to BS 6465-3:2006 Sanitary installations. Code of practice for the selection, installation and maintenance of sanitary and associated appliances⁷); after-market supply flow restrictors; and energy-efficient low-consumption washing machines and dishwashers.

In addition, the use of water meters acts as a useful incentive to reduce consumption. Around 40% of households are currently metered⁸, but this is forecasted to rise to 85% by 2035.

Conclusion

Regardless of personal opinion on the validity or otherwise of the theory of climate change, the fact remains that during extreme weather events buildings have a tendency to fail. This can be due to a number of factors, and under certain circumstances can be due to conflicting requirements on the building envelope. However, as has been identified, there are numerous systems and products available with which to combat weather and climate extremes. In order to assist in producing buildings that are better able to withstand the vagaries of the weather over their design lives, the NBS offers a number of subscription products from which systems and products may be specified to mitigate the effects of climate change.