Green roofs
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Green roofs reduce atmospheric CO₂ levels and capture rainfall and air pollutants. Plants on the roof not only support biodiversity on the site, but also insulate the building, leading to reduced cooling costs.
Environmental benefits
- Capturing CO2 from the air.
- Reduction of heat island in the city.
- Reducing dust and capturing pollutants from the air.
- Promoting biodiversity through appropriately selected vegetation.
- Podpora biodiverzity pomocí vhodně zvolené vegetace.
Economic benefits
- Reduction of building cooling costs.
- Reduction of the stormwater drainage fee for business and public entities.
- Protecting the waterproofing and extending the life of the roof.
- Increase the coefficient of greenery on the plot.
- Increase the usable area of the property.
- Possibility of use for local food production - urban agriculture.
Social benefits
- A space for people to meet naturally.
- Possible addition of a functional garden for growing crops.
- Connection with roof terrace and possibility of greenery in dense urban development - reducing people's stress, recreational benefits.
- Improving the microclimate inside the building.
- Sound insulation - improvement of airtightness by up to 6 dB.
- Enhancing the aesthetics of the building.
Why use this solution
Green roofs can trap CO₂ in the air and incorporate it into the vegetation layer. However, to assess the overall CO₂ savings, it is necessary to consider whether more material needs to be used for the roof structure. A green roof also captures dust particles from the surrounding air.
A green roof provides protection for the roof waterproofing from the elements and from damage during roof maintenance, extending its life up to twice as long. During torrential rains, it captures part of the rainfall and does not overflow the sewerage network, and it is possible to reduce the costs of seepage or retention facilities (according to Annex 16 of Decree No. 244/2021 Coll.).
Green roofs are an effective control of temperature fluctuations, ensuring thermal comfort and the associated savings in indoor air conditioning costs. In winter, the opposite effect occurs, with a reduction in heat loss.
By combining green roofs with PV panels (so-called biosolar roof), it is possible to achieve higher efficiency of PV panels, as the panels have higher efficiency at lower temperatures. The fact that the panels provide shade to the green vegetation makes room for more valuable vegetation in terms of biodiversity.
The green roof area can also be used in the calculation of the green coefficient, so it is advantageous to consider the roof at the beginning of the project, when it can increase the buildability of the land for the investor.
An indirect economic advantage of the technology is the increase in the price of a house with a vegetated roof on the real estate market. The aesthetic value and increased attractiveness of the building and its surroundings is related to the increased attractiveness and prestige within the corporate culture and the labour market. This benefit is an important factor on which productivity, employee satisfaction and loyalty are based. This will have a positive effect on the investor's economy, for example in terms of lower employee sickness or lower costs associated with employee turnover.
Implementations and projects
Afi Butterfly
Prague, Czechia
source: AFI
AFI Karlín Butterfly office building - green roofs and walls turn the building into a living organism that grows and changes with time. At the same time, the facades insulate the building and produce oxygen to the immediate surroundings, retain water and improve acoustic conditions in the immediate vicinity.
Liko-Vo
Slavkov u Brna, Czechia
source: LIKO-Vo
Industrial hall LIKO-Vo in Slavkov u Brna - The building uses the concept of "living buildings" based on natural thermal stabilization. This is provided by a green roof and facade, a retention pond and other technologies.
family house in the valley of Dyje
Znojmo, Czechia
source: BoysPlayNice
Family house in Znojmo - The land is a gap between family houses that form the embankment of the river Dyje. The roof is covered with an extensive green roof.
Main Point Pankrác
Prague, Czechia
source: DAM architekti
photo: Andrea Thiel Lhotáková
Office building with a green roof on a 40 m high building. The roof serves as a living space and is one of the big attractions for tenants. It meets ecological requirements and is a converging social aspect for the occupying community.
How the solution works
There are several types of green roofs: extensive, intensive, semi-intensive, blue or biosolar. These types differ according to the thickness of the layers, the green cover installed, the amount of water retained and the technologies involved.
Green roofs are commonly implemented on roofs up to a pitch of 45°. Higher pitches require atypical and complicated solutions and are therefore implemented minimally. Intensive, semi-intensive, blue-green and biosolar roofs are generally limited to a slope of up to 5°. Extensive roofs up to 5° have a multi-layer system, from 5° to 15° a single-layer system, and from 15° upwards require a slope restraint system and the use of pre-grown vegetation mats. It is also important to consider the exposure of the roof and the effects of natural influences (sun, wind, snow, ...).
Green roof evaporation diagram
Types of green roofs
Extensive roof
The extensive roof has only a low thickness of vegetation layer, from about 5 to 20 cm. With a thickness of 10 cm, the roof can absorb up to 50% of the rainwater fall per year.
This type is suitable for roof constructions with lower loads. The weight of the vegetation layer is between 80 and 300 kg/m² in the water-saturated state. The extensive green roof is uninhabitable, but occasional movement of maintenance personnel is easily possible.
The thickness of the substrate determines the composition of the vegetation. Plants selected for this environment will be low and drought-loving to cope with extreme drought, heat and frost conditions. Suitable plants are plants of the genus Sedum (sedum) or lower arid-loving herbs and grasses.
The extensive roof is low maintenance - maintenance is required once or twice a year and mainly involves weeding, checking run-off and fertilising if necessary. It primarily serves ornamental, retention and insulation functions. The installation of an irrigation system is not necessary.
Intensive roof
The intensive roof reaches the higher layers of the vegetation layer, usually from 20 cm upwards, but up to 150 cm depending on the needs of the plants chosen. Trees can also grow on an intensive roof.
Suitable for roofs with high load potential. The weight of a green roof can range from 300 to 2,000 kg/m² depending on the vegetation chosen. Intensive green roofs are residential and allow more frequent movement of people.
The vegetation on these roofs can vary from lawns, to more demanding perennials, to planting shrubs or low trees. It requires intensive maintenance and regular irrigation.
Semi-intensive roof
A semi-intensive green roof combines an extensive roof in some places and an intensive roof in other places. Suitable for roofs where some parts of the roof need to be lightened and others can be made more heavy. A semi-intensive green roof offers a greater variety of habitats and allows the extent of the sub-areas, their use and maintenance to be adapted.
Blue roof
A blue (blue-green) roof consists of storing rainwater under a drainage layer. This water can then be reused or runoff can be significantly slowed down.
Suitable for areas with a high percentage of impermeable surfaces that drain rainwater into drains.
A special retention and drainage system is installed on the roof, which is covered with vegetation. The inlets can also be fitted with elements that allow water to be retained on the roof and thus regulate runoff, which can even achieve zero runoff in the event of extreme rainfall events.
Biosolar roof
A green roof combined with a photovoltaic system.
Biosolar roofs are usually extensive with a load of 150-200 kg/m². They are suitable where the roof is not expected to be used for the movement of people and where there is a requirement for renewable energy generation.
The vegetation area overloads the supporting structure for the PV panels, so there is no need to anchor it into the structure, minimising the risk of leakage. At the same time, the support structure is elevated above the roof surface, allowing plants to grow throughout the
Economic parameters and subsidies
Cost of investment
The investment costs of building a green roof include:
project preparation,
implementation works,
materials for the creation of the drainage/separation/protection layer,
drainage gullies,
lightweight structural substrate,
specific type of vegetation,
fertiliser,
duckweed/gravel for roof loading that also serves as mulch.
Extensive roof greening is used on roofs with a load capacity of 60-300 kg/m². This is the least expensive option with a substrate thickness of up to 10 cm, where seed (approx. 25 CZK/m²), stonecrop cuttings (approx. 40 CZK/m²) or stonecrop carpet / stonecrop mats (approx. 440 CZK/m²) can be used. The total price of an extensive green roof is then around 1800-2,500 CZK/m², this price includes the composition above the static part of the roof.
Intensive vegetation planting requires a higher static load capacity, which should be calculated for the specific type, tentatively up to 1,000 kg per m². An intensive roof can take many different forms, from lower perennials (about 30 cm), to meadow vegetation, to the use of taller shrubs. The price for intensive vegetation is between 1,500-5,000 CZK/m².
Operation and maintenance costs
Vegetated roofs are divided into extensive/semi-intensive/intensive based on the degree of vegetation self-regulation, i.e. the extent to which vegetation functions without human intervention. Extensive roofs are virtually maintenance-free (maintenance once or twice a year), while maintenance on intensive roofs varies according to the vegetation chosen (approximately once or three times a year).
The scope and tasks must be determined on a site-specific basis, depending on weather conditions and the form and development of the vegetation. As a rule, they include:
irrigation for the time necessary for the rooting of plant cuttings, seed germination and rooting of vegetation mats,
starter fertilisation,
plugging the joints of the vegetation mats,
weed removal,
replanting,
and others.
Subsidy opportunities
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It is possible to use the subsidy under the New Green Savings Programme in the 2021-2030 programme period, and a separate subsidy title for green roofs is now available. The subsidy can be applied for both new buildings and renovations. The amount of the subsidy depends on two criteria. The first is the type of roof (extensive/intensive), the second is the slope of the roof (flat/sloping roof).
The amount of the subsidy ranges from CZK 800 to 1 000 per m². For family houses, the maximum amount of the subsidy is limited to CZK 100 000, where the support may not exceed 60 % of the cost of implementing the green roof. For apartment buildings, the limit is set at CZK 400 000.
Another subsidy can be obtained from the Green Roofs Grant Programme, which is intended for all buildings in Brno, which is regularly available.
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The grant can be obtained from the Operational Programme Technologies and Applications for Competitiveness (OP TAK).
Supported activities include, among other things, revitalisation of company premises and the surroundings of commercial buildings to adapt to climate change, for example by planting functional vegetation and establishing so-called vegetation roofs.
Environmental benefits
All types of vegetated roofs have a significant impact on the microclimate around the house and its thermal comfort, as they significantly reduce the thermal fluctuations of the living space under the roof in summer and winter months.
Conventional waterproofing warms up to 80 °C in the summer months, whereas a green roof only warms up to 35 °C. Green roofs can therefore act as a complement to thermal insulation, which can reduce the temperature of the roof surface by up to 45 °C on a sunny day.
Rainwater runoff from a conventional concrete roof with waterproofing ranges from 95 to 100 %, while a green roof can reduce this to an average of 50 %. However, there are also types of green roof that can reduce runoff to as little as 5 %. The subsequent evapotranspiration (evaporation of the captured water) modifies the microclimate of the building and its surroundings. 1 mm of rainfall retained per 100 m2 of vegetated roof equates to a saving of 70 kWh of energy needed to cool the building.
Furthermore, 1 m2 of green roof can absorb up to 5 kg of CO₂ and 0.2 kg of dust particles per year.
Comparison of solutions
| Green roof | Roof without vegetation layer |
|---|---|
| Capture rainwater at the point of impact. The amount of rainwater captured depends on the technology used. | Rainwater flows into drains or other retention systems such as storage or detention basins. |
| The green layer cools the surfaces and their surroundings. | In the warmer months, overheating can occur and affect thermal comfort even inside the building. |
| Extending the life of the waterproofing. | Faster ageing of the waterproofing. |
| A green roof with the possibility of staying significantly affects the psyche of its users. | A roof made of solid materials contributes to the formation of a heat island. |
| Vegetated roofs increase the green coefficient for the project and promote biodiversity. | Zero biodiversity support. |
Contact the architect and designer
The first step for new builds is to contact an architect or designer with a green roof requirement. Green roofs have their own structural requirements and can affect the design of the entire building. It is therefore important to know the required function of the roof in advance. In the case of existing buildings, the possibilities should be considered first. Depending on the function, use and possibilities of the building, the appropriate type of greening is selected.
Contact a structural engineer for a structural assessment, evaluation of the waterproofing condition and other structural prerequisites
Before installing a green roof on an existing building, a structural assessment of the structure is usually required. For new buildings, it is important to think about green roof loading at the design stage. The structural assessment then determines the green roof options (intensive/extensive etc.). The waterproofing of the roof of an existing building must be in good condition and resistant to root penetration.
Approach a landscape architect or green roof contractor and consult with them on the design
The vegetation layer of the green roof is adapted to both the building's capabilities and then the target vegetation. Plant species and vegetation layers should be selected by experts (horticulturists, landscape/landscape architects, landscape contractors) so that the vegetation is sustainable and functional in the long term.
The designer and landscape architect will prepare the implementation documentation for the green roof
Documentation to be prepared in consultation with the landscape architect and according to the green roof contractor's submittals to maintain quality.
Select contractor and implementation company
The contractor will implement the green roof
The supervision of a landscape architect and designer is essential during implementation.
Select a maintenance company
Maintenance is specified by the landscape architect, designer or contractor depending on the type of vegetation proposed.
Consultants and suppliers
Consultants
Consultants and energy specialists should be contacted if the photovoltaic panels are to be combined with a green roof. The consultants will calculate the energy balance of the building and suggest the size of solar installation required.
Suppliers
They will supply the material and then implement the project according to the project documentation.
Planners
The designers, who are mainly landscape architects, will prepare the documentation for implementation.
Updated: february 2024