Green Roofs

The term “green roof” refers to a building’s terrace or roof and to a city block’s inner courtyard – with a garden on it. And green roofs provide direct benefits for the estate they are installed in: a ludic place for the neighbors; a longer-lasting roof; an increase in the value of the building; a reduction of the electricity bill, especially if solar panels are used, because of a higher energy efficiency; and a possible reduction of taxes.

Additionally, green roofs yield benefits everyone can enjoy too, such as the absorption of pollutants, improving the quality of the air; the absorption of CO2; the reduction of water runoff; the increment of the number of green areas, which promote urban biodiversity; the palliation of the heat island effect in the urban center, achieving additional reductions in CO2; and acoustic insulation.

Green roofs can be extensive or intensive and are definitely compatible with other projects such as vegetable gardens, solar panels and/or recreational areas.

Green roofs and terraces are also categorized based on if they are traversable or not. In case they are not, an extensive green roof with herbaceous or sedum plants, which require little substrate (weighing about 220-330 lbs or 100-150 kg / m2) and little maintenance (minimum twice a year), would be recommended.

If the terrace is traversable, other heavier and higher maintenance types of green roofs come into consideration: semi-intensive ones, with herbaceous plants and low shrubs; and intensive ones, which have substrates ranging up to 50 cm deep so as to allow the growth of all plants, including trees.

the best moment to install a green roof is when you renew your roof’s impermeable layer.

Did you know that, even though green roofs cost the same as an insulated roof, they reap so many more benefits?


Green roofs have countless benefits for citizens and for the environment. We summarize some here:

Thermal insulation

  • Innumerable studies show that a well-functioning green roof provides excellent thermal insulation. In our own experimental green roof we have observed that, in contrast with the temperatures of up to 60 and 70 ° C prior to it’s installation, 28 and 35 ° C are reached under the green roof’s soil.

Acoustic insulation

  • Households below the green roof can see noise reflection reduced by up to 3dB and sound insulation improved by up to 8dB.

Heat island effect:

  • The heat island effect, an effect that makes the city center 2 or 3 degrees warmer than it’s outskirts, would be palliated. This could lead to a reduction in air conditioner use and further reduction in carbon emissions.

Reduction of CO2 emission:

  • CO2 emissions would wane because:
    • plants absorb it
    • the heat island effect would be palliated
    • other CO2 emitting forms of insulation would be discontinued.

Water runoff:

  • The plants of a green roof naturally accumulate water for their future use, entailing a slower drainage, thus resulting in a smaller dimension of the sewage.

Urban biodiversity:

  • Increases urban biodiversity by maintaining the green corridors that range from Collserola to the Mediterranean Sea.
  • Increases the m2 of green / inhabitant ratio.

Pollutant particle absorption:

  • Absorption of polluting particles such as NOx and PM10

Albedo increase:

  • Albedo, which is the degree to which light is reflected by a surface, will increase. This is a benefit because unreflected sunlight will be absorbed and thus increase the temperature of the atmosphere.

Social aspects:

  • Enjoyable area for the residents of the building.
  • Urban agriculture km0 and the possibility of having a self-sufficient area of production.
  • Accessible private space to use in times of confinement.

Circular economy:

  • Possible installation of a rainwater-collecting tank to use for irrigation.
  • A composter can be installed to convert debris into compost.
  • Any lights or pumps installed can be run by renewable energy.

Economic aspects:

  • More durable roof as the substrate protects it’s waterproof layer
  • Increase of the value of the estate.
  • Possible decrease in sewer rate due to reduced water runoff when it rains.
  • Possible decrease in taxes of real estate.
  • If solar panels are installed, reduction of the electricity bill.

Frequently asked questions about Green Roofs

Do green roofs promote water leaks or moisture in ceiling?

On the contrary, the waterproof layer is protected from thermal influences. Green roofs must be installed on an irrefutably waterproof site: it must pass a watertightness test.

How are green roofs installed?

A green roof needs a series of technical layers to replicate a garden in the ground. After the waterproof layer, which has to be resistant to roots ( if you don't have one, you must install one specifically for that purpose), there is a protective and water-retaining blanket. The drainage layer provides a reservoir for rainwater and air that favors root development. On top of the drainage layer there is another layer that filters the particles so as not to saturate the drainage layer. And the finishing layer is the substrate. If it is an extensive green roof, it must be a mineral substrate with a depth of 8 - 15 cm. The plants will be in the sedum or in the grass family. If the green roof is semi-intensive, the substrate should be more organic and be 20 - 50 cm deep. The plants will be grassy and bushy, and small trees can be supported.

Is insurance provided for green roofs?

When the green roof and the waterproof layer are installed together, an insurance of 10 years is given.

What kind of green roofs can be installed?

The most important goal is to create a green roof that accommodates the uses the community wants it for. Within that there is an array of options: you could install paved or semi-paved paths to walk or to set up a table upon; you could set aside an area to hang clothes or to install solar panels; you could also destine an area to be a vegetable garden. The green roof may be apt to walk on or it may not be. We can install bigger or smaller plants according to the thickness of the soil, which will be determined based on design vectors and also by the weight that the building can bear.

My terrace is communal, how could I convince the rest of the neighbors to install a green roof?

We can attend the owners meeting; as well as present a preliminary proposal and budget to facilitate the conversation with the neighbors and be able to find suitable solutions for all doubts anyone may have.

What exactly is a roof?

We use the generic term “roof”, but it could refer to a variety of different surfaces including private terraces, communal terraces, ones with asphalt or with ceramic fabric, on top of buildings or in a block’s inner courtyard.

Does the government offer any subsidies?

Depending on the City Council of each municipality, through the Consorci d'Habitatge (Housing Consortium), a financial aid of 30% of the costs could be given for the rehabilitation of a building, but if there is an action that improves energy efficiency such as a green roof or solar panels, the subsidy could amount to up to 50% of total costs. L’Institut Municipal de Paisatge Urbà de l’Ajuntament de Barcelona (the Municipal Institute of Urban Landscape of the City of Barcelona) has also launched a competition that rewards the winning green roofs with a 75% subsidy.

What is the approximate cost of a green roof?

Roughly an extensive green roof including automatic irrigation and waterproofing would be around 150 EUR / m2. Without waterproofing we would be talking about 100 EUR / m2.

Can my building have a green roof? Is it necessary to reinforce its structure?

As a general rule, all buildings can have some type of green roof depending on the solar incidence and the structural load. We take care of the structural analysis, the landscape design, the project, the building permit, the execution and the maintenance. In the structural analysis phase we will take into account all the green roof options that do not require structural reinforcement. However, we may need the building to be reinforced in specific situations due to previous anomalies or because more substrate than necessary is wanted.

What is the maintenance of the green roofs like?

If the green roof is extensive, maintenance is minimal. It would be a visit once a month or trimester to ensure that the drains are free. If it is intensive, we recommend 12 - 18 visits per year, as the plant maintenance would include pruning, fertilizing, substituting, checking watering, among other tasks.

Latest projects of Green Roofs

See more