A rooftop or green roof It is the upper deck of a building or house where a topsoil has been established. This technique has its origins in the ancient living grass roofs of Norway and gained momentum in Germany during the 1960s..
The purpose of green roofs is to save energy, regulate the temperature, filter the air, absorb CO2 and efficiently manage rainwater. Therefore, they are technologies with an ecological function and not simply areas of the roof where potted plants are arranged..
To make a green roof, a special preparation of the support on which the crop is to be established must be carried out. It consists of a stratified system at the base of which is an additional waterproofing layer of the upper roof cover..
Subsequently, a succession of layers is placed that allow drainage, prevent the development of the roots towards the ceiling and provide a suitable substrate for the plants..
There are green roofs of various types, such as extensive roofs, low load and low maintenance, with herbaceous or succulent plant cover. Likewise, there are intensive ones with high load and maintenance that include from herbs to trees and semi-intensive ones that are intermediate variants..
Green roofs provide various benefits such as thermal regulation, energy saving, air purification, use of water, recreation, among others. The disadvantages are the structural risks that they can imply for buildings and maintenance costs..
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The antecedents of green roofs are located in Norway between the seventeenth and nineteenth centuries when the roofs were covered with earth and grass was laid. This technique was used mainly to regulate the temperature of the house.
Later, during the 19th century, settlers in the United States used this technique to solve the shortage of wood for the roofs of houses..
Also, in Germany in the same nineteenth century houses were built with roofs covered with tar as waterproofing that caused devastating fires. Because of this, roofer Koch proposed covering roofs with sand and gravel to reduce fire hazards..
This type of substrate allowed the development of herbs in a natural way that covered the entire roof and made it waterproof and very resistant. In fact, by 1980 there were still houses with these original roofs in good condition..
The modern boom in green roofs developed from initiatives in Germany in the 1960s. It is currently estimated that about 10% of roofs in Germany are green.
This trend has spread to many countries both in Europe and America where you can find important buildings with green roofs. Among these we have the Frankfurt airport (Germany), the Vancouver Public Library (Canada), the Palais Omni Sports in Paris (France) and the Santander Bank of Madrid (Spain).
A green roof is made up of a layered system made up of a series of layers with defined functions. These functions are to prevent seepage, drain water and provide substrate for plants..
A central element in green roofs is to prevent seepage since the vegetation cover retains a large proportion of water. Even when some of this moisture is consumed by plants, the surplus must be properly dislodged..
In addition, it must be guaranteed that the waterproofing is long-lasting since repair costs are high because the entire upper system has to be dismantled..
Above the waterproofing layer should be established a layer designed to allow the drainage of excess water. It is a structural layer that allows the movement of water between the lower waterproofing layer and the upper anti-root layer..
One of the risks of green roofs is the potential root damage to the roof structure. The roots can be highly developed and cause problems to the roof covering such as leaks or more serious structural damage..
For this, it is necessary to place a layer that prevents the development of the roots beyond the substrate layer..
Plants require a substrate in which to take root and that supplies them with the essential nutrients for their development and survival. This substrate can consist of a soil mixture or an absorbent artificial substrate that is irrigated with nutrient solution..
Finally, the selected species are sown on the substrate layer that has been established. The selection of the species to be planted will depend on factors such as climatic conditions, structural conditions of the roof and the established design criteria..
Depending on the climatic conditions in the area, the green roof will likely require irrigation at least one period of the year. If required, drip irrigation is recommended for the most efficient use of water.
They are low maintenance, generally installed in inaccessible places and mainly include herbaceous and succulent plants. On the other hand, depending on the species selected and the geographical area, it may not be necessary to apply irrigation or fertilization..
The thickness of the plant substrate is 5-20 centimeters because the sown species have shallow root systems and grow horizontally. Its maximum weight completely saturated with water does not exceed 200 kg / m2 and its maturation process lasts around four to six months..
They are generally designed to be accessible to people and can be used for recreation. Its maintenance is intensive and requires constant irrigation and fertilization.
This type of green roof can include a wide range of biotypes and species from trees, shrubs of different sizes and herbaceous plants. The design possibilities are very great and foliar tones and flower colors can be combined.
It is recommended to use species that are adapted to the climatic conditions of the project site. The plant substrate layer is from thirty-five centimeters to more than one meter.
The structural load in this type of roof can range from 250 kg / m2 to 1,200 kg / m2 and its maturation can take several years.
Combine both designs and divide the load according to the structural characteristics of the property. The thickness of the substrate ranges from 12 to 30 cm and the weight of these installations can vary between 120 and 250 kg / m2..
Likewise, green roofs can also be classified according to their particular use. Therefore, there are green roofs for gardens, water accumulators, energy generators and for recreation, among others..
There are many material and design alternatives for the establishment of a green roof. The selection of the most appropriate depends on the structural characteristics of the property, available budget and use..
It should be taken into account that a suitable design and materials will allow its long-term enjoyment and with relatively low maintenance costs..
The most complex phases in establishing a green roof system are waterproofing, structural bearing capacity, and drainage water management. If you do not have the appropriate technical knowledge, it is best to use the services of a specialist..
The first thing is to define if the green roof will be ornamental, food or for the cultivation of medicinal plants. In addition, it should be taken into account that the size of the plants to be used is limited by the load capacity of the roof..
An evaluation of the structural characteristics of the building must be carried out to know its load capacity. For this, it is best to consult a civil engineer, architect or master builder..
The selection of plant species to be cultivated is determined by the use of the green roof, the structural limitations of the building and the climate of the area..
It should be taken into account that the incidence of solar rays, the temperature and the wind regime are affected by the location and height of the property. When selecting food plants, additional care may be required to control pests and diseases..
In intensive green roofs it is possible to apply the full range of landscape design possibilities combining annual and perennial plants with different flowering periods.
For extensive roofs, grasses are generally used, which require more frequent watering during the summer. When it is not possible to have an irrigation system, it is recommended to use succulent plants such as cacti or species of Sedum, Sempervivum or Delosperma.
It is essential to check the condition of the waterproofing layer of the external roof covering and assess whether the surface is well leveled. If there are any problems, the waterproofing layer must be repaired or replaced and the necessary level corrections must be made..
Establishing a green roof requires an additional waterproofing layer that is long-lasting to avoid having to replace the system. For this, waterproofing systems must be installed with guarantees of up to 10 or 20 years and a useful life of 40 to 50 years..
This special waterproofing includes the installation of a layer of high-density polyvinyl chloride (PVC). When it comes to a roof (flat roof), it is essential that there is adequate leveling in the direction of drainage to avoid the accumulation of water.
It is necessary to install a layer over the drainage system that prevents the roots from entering the lower layers. This prevents clogging of the drainage or damage to the waterproofing layer..
The anti-root layer is resistant and filtering since it must allow the passage of water and prevent the passage of the roots.
A drainage layer must be placed that allows the passage of water, which may consist of a corrugated sheet or corrugated plate.
Likewise, a structural mesh with a filter layer can be used that allows the water from the upper substrate to pass through and disperse it to the drain outlets..
Above the drainage layer it is convenient to include a filter layer that prevents the passage of coarse particles of the substrate that could obstruct the water outlet.
Subsequently, on the filtering and anti-root layer, the substrate layer is deposited, the composition of which will depend on the type of plants to be established. It is very important that the texture of this layer guarantees adequate moisture absorption without excessively retaining water..
The most suitable substrate is a system of horizons that has a layer of sand and fine gravel at the base and on top of this a mixture of clays with fertile soil..
Once the substrate has been established, the sowing of the selected plant species must be carried out. For some plants such as grasses or lawns, pre-seeded rolls can be placed and quickly set to the substrate.
In the case of other plants, the seeds or seedlings obtained in the nursery can be sown directly.
Generally, green roofs require very little maintenance, such as periodically checking the drains to verify that they work properly..
On the other hand, it may be necessary to carry out irrigation at least during the dry period to guarantee the adequate development of the plants. In this case, the most suitable irrigation systems are sprinkler or drip.
In cities there is a great abundance of concrete and asphalt as well as air conditioning equipment and vehicular traffic that produce an environment of high temperatures. Therefore, the so-called albedo effect or urban heat island effect occurs..
Albedo is a measure of the amount of solar energy that is reflected by a surface and therefore is not absorbed as heat. Urban areas have an albedo that is 10% lower than rural areas.
In this sense, green roofs help regulate the temperature of buildings by reducing the incidence of ultraviolet rays on the outer roof covering. It has been estimated that using green roofs can reduce the use of air conditioning devices by up to 40%.
Green roofs help reduce the greenhouse effect and reduce global warming. This is because plants are carbon sinks, since they trap the CO2 generated in the city to carry out photosynthesis..
Plants are natural air filters as they absorb CO2 and release oxygen and thus help purify urban air. On the other hand, green roofs have been found to reduce sulfur dioxide and nitrous acid in the air by 37% and 21% respectively..
When rain falls on a conventional roof, it directly impacts the outer covering causing an erosive effect. Likewise, when faced with a smooth and uncovered surface, the flow rate and its displacement speed increase..
Another problem in cities are sewage saturation events (overflow) that produce water courses capable of carrying large amounts of waste. These wastes can end up in rivers or the sea and generate pollution.
For example, in New York City it is estimated that 50% of rainfall events end in overflows. It has been estimated that they provide 40 billion gallons of untreated water annually.
On the contrary, in a green roof the vegetal layer and the substrate cushion the impact of rainwater. In this way a part of the flow is absorbed and the drainage speed is reduced..
In addition, the green roof system protects the waterproofing layer, reduces the risk of sewer overflow and prolongs the useful life of the drainage system.
The outer covering of a roof is subject to large temperature variations, particularly in areas with marked seasonal changes. In a study it was shown that an uncovered roof can suffer diurnal variations of up to 50ºC and with a system of green roofs it is reduced to only 3ºC.
Therefore, a well-managed green roof contributes to increasing the service life of the waterproofing of buildings. The vegetation cover layer moderates temperature changes and protects against solar radiation.
The vegetal layer dampens urban noise and improves the acoustics of the area. In this way it contributes to the sound insulation of the property.
Green roofs with a suitable landscape design are a relevant decorative element. On the other hand, in the case of green roofs they become a place of recreation.
On the green roofs it is possible to grow food and medicinal plants that can be used for the consumption of the inhabitants of the building. However, it should be taken into account that these plants require additional care to ensure effective production..
According to international studies, when a green roof is placed, the capital gain of the property can increase by up to 15% in the real estate market. This is because they generate significant energy savings and improve quality of life.
Likewise, the investment in the installation of green roof systems can be treated as a maintenance expense. Therefore, this investment may be tax deductible..
If not installed properly, green roofs can cause moisture problems, leaks, or even structural damage to the building. Some species of plants have an aggressive root system and can reach the outer covering of the roof and cause damage..
On the other hand, the green roof system represents an additional weight on the building that must be carefully considered in order to avoid accidents..
The average cost of establishing a green roof can be two to three times that of a conventional roof.
A traditional roof only requires adequate periodic supervision to assess the condition of the waterproofing mantle. In the case of intensive green roofs, maintenance must be regular to guarantee their proper functioning..
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