More torrential rain

Preparation of new construction for more and heavier rainfall

As climate change takes hold, we will experience more days of heavy rain, increasing the total precipitation in summer and winter. Although it will rain less in the summer, we will get more frequent and violent cloudbursts.

When choosing a building site and the placement of buildings, it is vital to consider protection against flooding. When preparing the building site, it is possible through reasonable terrain regulations to ensure the diversion of rainwater away from buildings and paved areas in a controlled manner. At the same time, there is a need to consider ways to collect rainwater to the greatest extent possible, filter it down through fascines, or actively use it on the site and in connection with the building’s operation. A combination of fascines with ground heating systems can be advantageous - see the report "Development of fascines with ground heating hoses" below.

Some roofs and decks with vegetation, called green roofs, can absorb and retain some of the water when it rains. In optimal situations, green roofs, properly executed, can absorb and evaporate up to 60 to 80 % of the precipitation that falls on them over the year.

The construction designers must take the risk of heavy rainfall into account. The roof design must ensure the collection and direction of rainwater away without the risk of backflow and that snow cannot accumulate in heavy drifts in winter. The sizing of roof surfaces, gutters, and downspouts must enable water diversion from a heavy downpour. Establishing emergency drains for large roof surfaces, where an accumulation of water can be critical for the load-bearing structures, might be necessary.

Temporary or permanent bulkheads can prevent surface water from running through doors or via stairs below terrain level. Protection of basement stairs, light shafts, etc., might be possible using raised edges.

If flooding threatens specific installations, such as basement drains, it can be necessary to establish a backflow prevention valve in the wastewater line near the installation subject to flooding. There should not be wastewater supply upstream of the backflow prevention valve, and rainwater supply and drainage must occur downstream. Backflow prevention valves are limited to a small group of users, such as in single-family houses.

Another option for protection against flooding in buildings is a bypass system. It consists of a backflow prevention valve and a pump system. During normal operation, gravity diverts the wastewater to the main line. During flooding, the high-water valve closes, and an overflow directs the wastewater to the pumping system. The use of bypass systems is possible for small and large user groups, e.g. apartment buildings, and in both single and two-line sewer systems.