Permeability rate: compliance with legislation and protection of the environment
As one of the first steps in the development of an architectural project, the study of the legislation in force on the ground is of paramount importance for the success of the proposal. Through calculations and restrictions, zoning laws present limits to be taken into account in projects which, therefore, encourage architects to think of intelligent solutions, dealing with these limits in a practical and creative way.
These parameters are dictated by the government and aim to stop, maintain or accelerate urban growth in certain parts of cities. They are norms that establish guidelines for the occupation of land, delimiting the percentage of built-up area, setbacks, distances, permeability, among others.
In the case of the permeability rate, we generally approach the soil’s ability to absorb rainwater. In other words, this index represents a percentage in square meters inside the land that must be kept free of constructions, allowing rainwater to seep into the ground and reach the water table. In most Brazilian cities, this percentage is around 15-30%, but there are rural areas where it reaches 80%.
Ensuring soil permeability is key to reducing the impact of urbanization on nature, as the creation of obstacles to the natural flow of water eventually promotes flooding. In this sense, it is up to the architect to design strategies that respect legislation and the environment, but at the same time allow the creation of pleasant spaces around, resulting in inviting and welcoming open spaces, such as gardens, patios or backyards that are functionally and volumetrically combined with the building.
Of the strategies, perhaps the most obvious of all is the use of vegetation cover, creating woodlands. However, other materials that allow water absorption can also be used, while also stimulating different appropriations and uses such as wooden decks, drainage plates, hollow concrete blocks, interlocking blocks, as well as natural elements such as stones and pebbles.
In Casa AA, built in the countryside of Minas Gerais, for example, in addition to the grassy spaces, much of the exterior area was paved with interlocking blocks without grout and with a small gap between them, allowing soil permeability. In this line, Brick Lattice House, although geographically distant from the first and located on a much smaller plot, uses the same strategy, with interlocking blocks. Through the blocks, the two houses increase their useful surface, creating extensions of the interior living spaces while guaranteeing the permeability of the soil.
Wooden decks overlapping the natural terrain are also attractive features when the design intent is to create outdoor living spaces. MJA House, in Portugal, presents a series of floating terraces on the ground that praise and respect the natural environment, protecting the water cycle and generating pleasant spaces to live and move.
There are also larger-scale projects that mix different strategies to maintain soil permeability, including FL Residence which, in addition to generous gardens between volumes, also includes large areas with wooden terraces without sub-flooring and stone slabs positioned in the middle of the grass. It is possible to notice that each strategy used in the house allows a different use and perception of space, improving the experience of users and their contact with the environment.
Another example that mixes different materials while maintaining soil permeability is Pátio Residence, which uses not only the cut slabs, but also rectangular stone blocks and loose pebbles that delimit the patio, creating a natural cover that differs from the grassy areas.
Finally, it is worth mentioning the use of draining soils as an alternative to maintain the permeability of the soil, since, thanks to advanced technology, some brands are able to reach up to 98% drainage capacity, in addition to to be a non-slip and thermally insulated alternative. The Porta Amarela house is an example of the application of this type of flooring outside, next to the swimming pool.
With this range of techniques and materials, maintaining soil permeability while respecting current legislation becomes an interesting exercise that allows the creation of different spaces and experiences. However, although some materials achieve almost 100% drainage capacity, it is important to note that none of them can be compared to a ground cover, because the roots of the plants prevent the soil from collapsing even when the water flow is intense.