AG02 WATER COLLECTION AND STORAGE IN BUILDINGS

Aim

In the design of the building, consider the potential for supporting the balance of the integral water cycle.

Why?

The progressive degradation and decrease of freshwater reserves worldwide makes it necessary to develop policies to increase the quality and quantity of available water resources.

The roofs of buildings can represent up to 50% of the impermeable surface area of a city, making them an element with great potential for collecting rainwater. The application of techniques to collect and store this water allows considerable volumes of water to be accumulated for reuse.

The benefits are diverse:
– The increase in available water resources, as the demand for drinking water supply decreases
– Water self-sufficiency, using rainwater for non-consumptive uses (toilet flushing, washing machine, cleaning and watering the garden, etc.), reducing domestic consumption of drinking water and the cost per housing.
– Help to reduce the risk of flooding, by not pouring the accumulated volume of water on the treatment networks, reducing the flows to be evacuated and purified.

How?

Integrating structures into the building, both in dwellings (single-family or multi-family) and in public, industrial or service buildings. They can be integrated in new constructions or restorations.

We can distinguish different systems for rainwater accumulation in buildings:

01 TANKS. Closed containers where the water collected on the building roofs is stored and carried to them through a pipeline. They have the advantage of being easy to install due to their size and low cost of construction and maintenance. They allow a multitude of designs and materials. Their size depends on the average precipitation in the area where they are located. Some can improve water quality through purification systems, or be implemented with a control of the filling start (the first 10 minutes of rain do not accumulate, cleaning the surface collector of pollutants).

They can be:
– Buried tanks for capture by gravity and re-use by pumping (Aljibes, prefabricated tanks).

– Rainwater tanks on individual terraces (Barrels)

02 GREEN ROOFS. Multi-layer systems located on the floor slabs of the building, where the collection and storage surface is the roof itself. They are designed to retain rainwater, improve its quality and allow its reuse in non-consumptive uses, but also to favour the growth of vegetation, lowering the temperature in the building and improving the urban landscape (See EV09). The physical and climatic conditions of the location (temperature, humidity, sunshine hours, vegetation species), urban morphology, building type and construction pattern define the green roof design.

They can be:
– Intensive vegetated roofs. Vegetation reaches a higher size, which will depend on the thickness of the substrate, and may be walkable. The roofs of underground garages can be used. Their storage capacity is on average 45% of their volume, producing flooding from 65%.

– Extensive vegetated roofs. Thin substrates (normally from 7 to 10 cm) that support low growth vegetation, sedum type, moss, aromatic and grass and any other vegetation that needs little or no maintenance. They are lighter, but not walkable. Their storage capacity is on average 20% of their volume, producing flooding from 65%.

03 THE BLUE ROOFS. Plain surfaces that work as a tank that stores rainwater. The water sheet can be visible or hidden under an extensive vegetation cover system, which avoids losses due to evaporation.Green roofs produce the following benefits:
– can retain up to 50% of the rainwater received, lengthening the runoff time and considerably reducing the harmful substances present in it, by accumulating rainfall over a period of time long enough to allow the removal of sediment and the purification of pollutants by the action of vegetation.
– Improvement of the quality of the water masses by acting as filters, reducing the load of pollutants that reach the sewers.
– They lower the temperature of the roof favouring a lower consumption of energy in the building (around 10%, being able to reduce the consumption of energy necessary for heating by 25% and 75% for cooling according to some studies).
-Mitigation of the heat island effect, providing natural cooling to the public space.
– Improvement of air quality by capturing atmospheric polluting plants (1m2 of green roof can absorb 5 kg of CO2 per year).
– Improve humidity levels and biodiversity in cities.
– Improving sociability, adding new meeting places and community use.
– Improved acoustic comfort, contributing to the reduction of urban noise.

Thermic behavior comparison in different types of roofs.

Source: F. J. Neila, C. Bedoya, C. Acha, F. Olivieri, M. Barbero. Informes de la Construcción, Vol. 60, 511, 15•24, julio•septiembre 2008. ISSN: 0020•0883. eISSN: 1988•3234

Diagram of collecting and storage elements in buildings

History Museum in la Vendée. Plan01 Architectes. Fuente: http://www.tectonica•online.com