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Garden green roof

11 min read
Garden green roof

If the structure of the building and the microclimate allow us, we can create a real rooftop garden, in the true sense of the word. In urban areas where even a small green corner is considered a luxury, we can create our own garden and bring nature closer to us on our roofs. Here we can admire how a small tree matures, how flowers are blooming and every morning we can feel the fresh grass tickling our foot.

The boring, grey roof can be changed with healthy vegetation, turf, shrubs, fruit-bearing trees and even vegetables.

And we shouldn’t forget about other benefits of a green roof either: it can adjust the temperature of the roof by limiting extreme variations, can mitigate the greenhouse effect, can reduce the Urban Heat Island and retains the excess rainwater etc. (see Advantages)

We can achieve all this by using the intensive and semi-intensive green roof building technologies, depending on clients’ preferences, specifications and structure of the building, climatic conditions of the area and the possibility of a long-term maintenance.
This type of vegetation needs special care, irrigation, proper fertilization and a 250-300 mm thick substrate. This thickness is important because of the great root mass and its need for moisture.

The garden green roof is especially designed for relaxing and recreation, and can only bear the medium pedestrian traffic. This must be considered when choosing the drainage course, which has to withstand compressive forces, to ensure water evacuation, without using other parallel systems.

This type of green roof doesn’t need really thick substrates, because high trees or voluminous root masses are not used. Even if it’s an intensive garden, can be landscaped on flat surfaces and pitched roofs too (5°-10° inclination).

Elements of a garden roof on a flat surface:

Protection, closing layer made of a membrane against root penetration
Protection layer made of a geotextile that ensures the mechanical protection of the membrane. It is made of polyester fibres and a mixture of mechanically consolidated fibres, polyester and regenerated polypropylene, having a moisture absorption capacity of 3-6 l/m², depending on the product.

A layer of drainage boards having the similar role of gravels, but with superior properties (gravel doesn’t have water retention capacity, because its own weight is too high etc.). Boards’ height is about 50-80 mm, they retain moisture and direct excess water toward “overflow” gutters. Depending on the model, they can stock about 10-21 l of water per m², having a weight of just 2-­4 kg/m². Intensive green roofs can bear pedestrian traffic too, drainage boards are resistant to compression between 25 kN/m² and 35 kN/m².
A 1-2 mm thick polyethylene cover forms the filtration layer, prevents clogging and filling of the drainage course with fine particles.
The vegetation substrate is the space for roots, so it’s decisive for the survival and development of plants. In case of semi-intensive green roofs its thickness is about 250-300 mm, depending on the aesthetic or functional factors. It is composed of recycled and natural materials, such as split face natural tiles, perlites, pumices, volcanic clays, peat fibres and biodegradable fibres, all as granules of 1-40 mm. The most important feature when choosing a certain substrate is the water retention capacity, which can vary between 25 and 40 % of the volume, and also the permeability and structural stability.

The vegetation layer itself can be the same as one on the ground, for example rich in plant species. Of course climate and microclimate and plants’ annual growth rate must be considered. It’s recommended to use native species of perennials or annuals, shrubs, vegetable plants, fruit-bearing shrubs etc. In case of woody plants, conifers and hardwoods, some features must be followed: undergrowth and shrubs, maximum height of 1,5-2 m; creeping or erect stems; to be adapted to drought (xerophile, xero­mezophile species) and to be resistant to frost.

In case of pitched roofs with gentle slope, the building structure of the extensive green roof is almost identical with the one of plane surfaces. An important and different feature is the lack of the filtration cover between drainage boards and the root substrate. The substrate is directly poured onto drainage boards, in order to ensure protection against slipping forces. Substrate must be continuously moistened until rooting, to prevent slipping and erosion. That is why it’s highly recommended to use vegetation rolls, especially turf. It’s well known that they can rapidly root, fixing all layers and protecting the entire green roof stratification.

Such a system can achieve 350 kg/m² in saturated status, and is 35-40 cm high.

Maintenance of an intensive green roof is performed in two different stages:
Maintenance after plantation, which can last about 2 years. This period is actually the consolidation of the vegetation.
Maintenance during service time of the green garden. This means irrigation, fertilisation, periodical inspections and removing dry plants and weeds. Garden terrace roofs need dedicated and accurate care, considering specifics for all seasons, growing and blooming period etc. This is the only way to achieve a controlled aspect.

Our company offers consultancy and system solutions for the landscape of green roofs and terraces, actually rooftop gardens with rich vegetation: turf, shrubs, fruit-bearing trees, even vegetables.

We are at your disposal with turnkey projects and long-term maintenance, using reliable building materials, plants especially developed for rooftop gardens and high quality vegetation rolls. Every landscape work offers the best cost/effectiveness/safety balance and every project is adapted to our customers’ aims.

We are able to landscape green terraces, intensive or extensive green roofs on the top of industrial halls, inside or outside vertical gardens for office buildings, and intensive green gardens with special relaxing zones, landscape green roofs with pedestrian traffic for shopping malls and many other ecological constructions.

To increase the ecological value of the building, photovoltaic panels can be also installed.
We are happy to help you with green projects, system solutions, estimates, and consultancy in the field.

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