Resilient Rainwater Systems
Rainwater systems collect and/or direct rainwater away from buildings. They comprise rainwater shedding details (such as projecting eaves); rainwater goods (eaves, valley, box or parapet gutters; outlets; hoppers and downpipes); gullies and below ground drains.
Rainwater systems are essential to keep a building in good condition and prevent its deterioration. If rainwater systems fail and water penetration occurs, this can cause fabric decay, such as timber rot. It can also affect structural elements (compromising foundations, for example) and create risks to the health of the occupants, including exacerbating mould growth. To function properly, rainwater systems must be well designed, adequately sized and appropriately detailed.
One of the impacts of climate change is the variations in rainfall patterns. There is a projected increase of around 33% in winter precipitation, and more frequent intense rainfall events. The UK is also expected to experience shorter but more concentrated wind-driven rain spells, especially in winter months. Notable increases are expected in projected annual wind-driven rain from west, southwest and westerly directions.
As a result, some rainwater systems are starting to fail. Sometimes this happens because the system has not been sufficiently maintained and repaired, but it can also occur because its design or capacity is no longer able to cope with changes in rainfall events.
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Buildings Without Rainwater Goods
Some buildings have traditional pitched roofs with deep projecting eaves that allow water to run off and be thrown well away from the property, without the need for downpipes or gutters.
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Inspection, Maintenance and Repair of Rainwater Systems
Regular inspections, routine maintenance and scheduled repairs are essential to ensure rainwater drainage systems perform adequately.
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Upgrades or Alterations to Rainwater Goods
Upgrades or alterations of rainwater goods is a response to design or capacity shortfalls.
Key messages
- Regular inspections, routine maintenance and scheduled repairs are essential to ensure good performance.
- If the rainwater system is failing, the first measure should be to improve the maintenance regime and/or increase the frequency of repairs. If this is not enough, upgrades or alterations may be necessary.
- Changes to rainwater goods on listed buildings or scheduled monuments as a response to design or capacity shortfalls are likely to be acceptable if the impact to the building's significance is minimised.
- Rainfall intensity values and building vulnerability to wind-driven rain vary depending on the geographical location of the building, its exposure and its orientation.
- There is no 'one size fits all' solution. Actions need to consider:
- the capacity and design requirements of the rainwater system
- the risks of damage due to spill over or overflow
- whether changes would affect the building's significance
- the cost of the works
