No. Green roof system does not include the waterproofing membrane, which is part of the construction of the building even without a green roof.
Technically, green roof system starts on the top layer of the building structure. In Portugal the most common situations are:
Note: all layers listed above must be dimensioned and will be different from project to project.
Waterproofing is not considered an element of the green roof system in all international technical guides.
Green Roofs correspond to vegetation installed on a constructed structure, regardless of the type of construction or type of vegetation. Only green walls built with climbing plants or vertical gardens systems are excluded. Typically they have a system with several materials arranged in layers, which must ensure the good development of the vegetation, respecting and promoting the physical integrity of the built structure.
Green Roofs have several benefits at different levels. Some of the main ones are:
- Rainwater retention capacity, reducing flood and problems in precipitation peaks.
- Microclimate improvement and consequent reduction of the heat island effect;
- Promotion of air quality through CO2 capture, oxygen production, as well as through the retention of airborne dust and particulate matter;
- Noise reduction;
- Promotion of biodiversity;
- Reduction of energy costs due to thermal insulation of buildings;
-Reduction of building maintenance costs by protecting the waterproofing membrane and reducing energy costs;
- Increase the presence of green spaces in cities
- Real estate valuation
- Possibility to produce fresh food in the roof
The Environmental Fund was launched in 2020 by the Portuguese Government, which finances the installation of green roofs and vertical gardens.
Eligible for private entities, who own existing and occupied dwelling buildings, single-family, autonomous fractions in multi-family buildings or multi-family buildings, built by the end of 2006. The contribution will be 70% up to a maximum amount of 3000 euros.
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No, on the contrary! Green Roofs increases the life of the waterproofing membrane. By stabilizing the temperature variation during the day, on the roof, the inclusion of a green roof reduces the wear and the formation of cracks in the membrane, due to the works of expansion and contraction that occur in this structure in the period of high heat (around 12 o’clock) and cooler (night), respectively. Infiltrations can be avoided with a good choice of waterproofing system, which must have anti-root characteristics and which, depending on the type of vegetation to be installed, must be protected by other additional anti-root screens and / or waterproofing.
Yes, as long as the building fulfils the conditions for the construction of a green roof, such as:
- Carrying capacity to receive the increased weight conferred by the green roof;
- The waterproofing membrane must be in excellent condition and preferably not at the end of its life, otherwise it is advisable to replace it.
Extensive Green Roof: green roofs of buildings or other constructions with a layer of vegetation that requires low maintenance once installed. Extensive green roof plants (succulent, herbaceous perennials) developed on a substrate layer with a maximum thickness of 15 cm and, in general, the vegetation does not exceed 50 cm in height. The weight of the substrate profile and vegetation is generally less than 120 kg / m2.
Intensive Green Roof: Green Roofs of buildings or other constructions with an intensive or semi-intensive treatment requiring high maintenance, similar of a conventional garden. Intensive green roof plants may be herbaceous, subshrubs, shrubs and trees. They are grown on a substrate layer with a thickness greater than 15 cm. The combined weight of the substrate layer and the vegetation is greater than 120 kg / m2.
Semi-intensive Green Roof: Green Roofs of buildings or other constructions with a mixed vegetation cover (intensive and extensive), requiring moderate maintenance. The vegetation of a semi-intensive green roof is usually composed of herbaceous, sub-shrub and bushy plants. They are grown in a layer of substrate with a thickness of 10 cm to 25 cm.
ANCV does not recommend specific companies or individuals, nor does it take responsibility for the products or actions of its members. However, we provide on our website a table with a summary of where to find the most varied services and products for green roofs, provided by our members:
Each project is unique and prices are always negotiated according to the solutions and different systems that can be used. Still, on average, extensive green roof in Portugal can cost between 40 and 70 € / m2, and intensive green roof can cost between 80 and 150 m2. These values are indicative averages and may suffer significant changes related to gains or losses in scale and logistical issues of access to coverage and means for distribution of materials in the roof.
Some points should be checked at least once a year for both intensive and extensive green roofs, such as:
- Drainage: it is necessary to check if the drop tubes have a clear passage of water
- Invasive plants: It is recommended to remove invasive plants that may damage drainage or the supporting structure, and tend to become dominant;
- Fertilization: according to the cultivated species, the need to fertilize and / or add organic matter must be verified;
- Irrigation system: maintenance and timely and adequate programming.
Food production on roofs is still an area under development. Many different species can be grown without problems, especially the more droughts tolerant ones, such as rosemary, thyme and chives. However, most of the traditional crops can be grown as long as an adequate substrate profile is provided (as well as an adequate substrate type), and irrigation and proper maintenance are ensured.
If the project is developed according to good rules / construction and maintenance of green roofs, especially according to the guidelines documents, there will be no problem. However, the most common problems due to design failures and / or execution and / or maintenance are:
Using soil instead of technical substrates: The use of soils instead of technical substrates in modern, multilayer green roof systems with low thickness leads to loss of soil profile structure; filter sealing and flooding in the rainy season, with the consequent death of plants. In extreme cases it can result in overloads that leads to serious damages on the building structure, possibly causing its collapse.
Drainage: Drainage problems are common, sometimes causing the death of the plants and localized overload problems that can lead to deformation in the structure of the building. For these problems to be avoided, it is recommended to carry the drainage according to measurements calculated with base on the area of the roof, also taking into account the maximum historical water flow of the installation site. The design should also be associated with a drainage project.
Structure: Modern green roof systems have brought significant advances in reducing the weight of green roofs. However, it is always necessary to take into account the technical specifications of the product / manufacturer and the load capacity of the building, in order to avoid cracks or even the collapse of the structure.
Death or poor development of plants: Problems with plants are usually associated with scarcity or excess of water (drainage problems leading to root asphyxia). It is important to carefully select species on a case-by-case basis, according to the type of use and maintenance intended for the green roof. The type of cultivating system used is also important.
Technical substrates, especially created for green roofs, are used because they are special mixtures of light materials, composed mainly of mineral components, with an organic content suitable for each type of green roof (extensive or intensive). Unlike soils, substrates are typically free of fine particles (limo or clay), or have very low percentages of these elements, a condition that allows them to maintain a good structure over time, as well as the assurance that the system will maintain the drain excess water over time.
Another interesting characteristic of the substrates is the absence of propagules, seeds or parts of weed species with high maintenance costs to control.
The fact that a good technical substrate is usually much expensive than a soil, which has a lot of meaning in big constructions, leads to the installation of soils in systems where they should not be installed, causing the failure of the green roofs.
Soils can be used in intensive roofs, constructed according to classic model. Soils must be strictly chosen, have a sandy loam texture and be free of weeds. They should only be used in intensive roofs with profiles over 40 cm, where drainage areas should not have filters / geotextiles, so that there is no medium to long term sealing. It should always be noted that soils do not have the same type of performance guarantee in the medium to long term, when compared to technical substrates.