Permeability Rate: Complying With Legislation and Protecting the Environment

As one of the first steps in the elaboration of an architectural project, the study of the current legislation on the ground is of paramount importance for the success of the proposal. Through calculations and restrictions, zoning laws present limits to be considered in projects that, consequently, instigate architects to think of intelligent solutions, dealing with such limitations in a practical and creative way.

These parameters are dictated by the government and aim to stop, maintain or accelerate urban growth in certain portions of cities. These are norms that establish guidelines for land occupation, delimiting the percentage of built-up area, setbacks, distances, permeability, among others.

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In the case of the permeability rate, in general, the ability of absorption of rainwater by the soil is approached. In other words, this index represents a percentage in square meters within the lot that must be kept free of buildings, allowing rainwater to infiltrate the soil and reach the water table. In most Brazilian cities this percentage is around 15% to 30%, but there are rural areas where it reaches 80%.

Ensuring soil permeability is essential to reduce the impact caused by urbanization on nature, as creating obstacles to the natural flow of water ends up favoring floods. 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 areas, such as gardens, patios or backyards that are functionally and volumetrically combined with the building.

Among the strategies, the most obvious of all is perhaps the use of vegetation cover, creating afforested environments. However, other materials that allow water absorption can also be used, at the same time also stimulating different appropriations and uses such as wooden decks, drainage plates, hollow concrete blocks, interlocking blocks, as also natural elements such as stones and pebbles.

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Milkbar House / Kennedy Nolan Architects. © Derek Swalwell

In Casa AA, built in the countryside of Minas Gerais, for example, in addition to the grassy spaces, a large part of the external area was paved with interlocking blocks without grout and with a small gap between them, allowing soil permeability. In this line, Brick Lattice House, despite being geographically far from the first and located on a much smaller plot, uses the same strategy, with interlocking blocks. Through the blocks, both houses increase their useful area, creating extensions of the internal living spaces while guaranteeing the permeability of the soil.

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Casa AA / Barino Arquitetura. © Bruno Meneghitti
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Brick Lattice House / Srijit Srinivas Architects. © Justin Sebastian

The wooden decks overlapping the natural terrain are also interesting elements when the design intention is to create outdoor living areas. MJA House, in Portugal, features a series of decks loose on the ground that praise and respect the natural environment, protecting the water cycle and generating pleasant spaces for living and moving.

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MJA House / Pereira Miguel Arquitectos. © Fernando Guerra | FG+SG
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MJA House / Pereira Miguel Arquitectos. © Fernando Guerra | FG+SG

There are also larger-scale projects that mix different strategies to maintain soil permeability, including FL Residence that, in addition to the generous gardens between the volumes, also features large areas with wooden decks without subfloor and stone slabs positioned amidst the grass. It is possible to notice that each strategy used in the house allows a different use and perception of the space, improving the users’ experience and their contact with the environment.

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FL Residence / Anastasia Arquitetos. © Bruno Pinheiro
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FL Residence / Anastasia Arquitetos. © Bruno Pinheiro

Another example that mixes different materials while maintaining the permeability of the soil 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.

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Pátio Residence / Arquitetura Gui Mattos. © Carolina Lacaz
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Pátio Residence / Arquitetura Gui Mattos. © Carolina Lacaz

Finally, it is worth mentioning the use of draining floors as an alternative to maintain soil permeability, since, with advanced technology, some brands are able to reach up to 98% of drainage capacity, besides being a non-slip and thermally insulated alternative. Porta Amarela House is an example of the application of this type of flooring in the outdoor area, next to the swimming pool.

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Porta Amarela House / Flávia Menezes Arquitetura e Interiores. © João Paulo Oliveira
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Porta Amarela House / Flávia Menezes Arquitetura e Interiores. © João Paulo Oliveira

With this range of techniques and materials, maintaining soil permeability while complying with current legislation becomes an interesting exercise that enables the creation of different spaces and experiences. However, although some materials reach almost 100% of drainage capacity, it is important to note that none of them can be compared to vegetation cover, as plant roots prevent the soil from collapsing even when the water flow is intense.