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Appeared in France at the beginning of the 90s, the greening of roofs remains unknown in our country whereas it is widely spread in Northern Europe. Example in the South West with a plant complex with an integrated irrigation system.

Vegetate your roof

Practical advice

Level: easy
Cost: € 99 / m2
Time: 2 days for 50 m2
Equipment: drill, hacksaw, cutting pliers or solid scissors, cutter, small tools
Vegetation that resists up to + 50° C
The sedum album (or orpin, a rock plant) was chosen primarily for its great resistance to thermal amplitudes (from -20° C to + 50° C).
In addition to its good adaptation to pollution and the lack of depth of land, it requires no mowing and self-regulating ceasing colonization as soon as space is lacking.

Variations in temperature have forced to ask the question of air conditioning buildings. There are, however, more environmentally friendly alternatives for regulating the temperature of a home.

Among these, the greening of the roofs. Behind this term hides an economic and light variant of the garden terrace: it is to develop on its roof a green space based on plants requiring very little maintenance on a substrate a few centimeters thick...
Where a garden terrace requires approximately 30 cm of topsoil on a slab designed to support the weight, revegetation will only result in an overload of 25 to 30 kg / m2; saturated with water.

Vegetation: a system suitable for roofs up to 30°

In both cases, it must first have made a perfect seal of the roof. Many manufacturers then propose extensive vegetation systems (Derbigum, Ecovegetal, Epdm Distribution, Eternit, Icopal Siplast, Priory, Meple, Sika-Sarnafil, Soprema, Toitvert, Velitex and Vertigo). Some of them can be implemented by knowledgeable individuals.

The revegetation complex can then be irrigated or not. In the system presented here (a kit of Vertigo), it is enough for a simple arrival of water (pressure of 1.2 to 2 bars) equipped with a tap of Ø 32 mm with a purge of emptying against the frost ( if necessary, a pressure reducer can be installed). It consists of a solenoid valve, a battery powered programmer, a rain sensor and the revegetation complex with its integrated watering system.

This system can be implemented on slopes from 0 to 30°. It first includes a drainage sub-layer (polyethylene mesh covered with a perforated geotextile). The objective is to dissociate the terrace of the vegetal carpet, to create an oxygenation of the plants, and to allow the drainage of the surplus of water in the event of heavy rain. This underlay is in rolls of 1.05 x 45 m.
Next comes a hemp irrigation mat (0.70 x 25 m rolls) fixed on a polyethylene mesh equipped with two irrigation pipes along the entire length. This carpet is used for rooting plants.

Finally the plants themselves in the form of rolled plates 1 m wide and 2 m long.

The implementation must take place between the last freezes and early October. The system is marketed in the form of kits of 15 or 25 m² customizable according to the plans provided by the customer. Indeed, if there are recesses in the roof (chimney, roof window, etc.), the bypass connections are included in the kit.

Green roof: minimum maintenance

At the end of two years, the revegetation settled definitively. The roots have penetrated into the two sub-layers and the whole is interdependent.
During this period, some loam is poured along the separation lines of the sedum plates, every three months in the first year and then twice a year. Cuttings are also scattered throughout the roof to reseed. This is a good time to apply a slow-release fertilizer low in nitrogen.

After a few months, you may want to plant other varieties of sedum, such as the sedum acre. Subsequently, it is even possible to add small flowers such as dwarf hyacinths or dwarf irises. However, if it is possible to walk on this vegetation for its maintenance, it is excluded to trample or occupy it for a prolonged period.

The interests of the green roof

In summer, the thermal protection action is of three types:
1) the complex creates a barrier against the sun's rays;
2) the irrigation generates a phenomenon of evaporation favorable to the cooling of the cover;
3) the air gap between the soil and the vegetation creates an additional insulating layer. These three associated phenomena can lead to a temperature drop (up to 5° C) in rooms under the roof.

In winter, the complex provides additional insulation, reducing the heating bill.

Finally, the green roof leads to an acoustic improvement of up to 8 dB.

The steps of installing a green roof

draining underlay for green roof

The roof must be perfectly sealed before installation

Directly placed on the waterproofing, the draining sub-layer is covered by the irrigation mat spread from one edge to the other of the terrace. The irrigation pipes of the carpet are noticeable on the visible side.

irrigation pipes for green roof

A 32 mm polyethylene (hose) nipple is positioned. In front of each irrigation pipe, a hole is drilled with a 6 or 8 mm drill bit, making sure to make this hole in the axis of the pipe to be connected.

green roof irrigation connections

Support collars are attached to the nurse at the right of each connection. They have a gasket that fits on the pipe. Tighten nuts to prevent leaks.

irrigate a green roof

The threads of the connections between the support collars and the carpet pipes are surrounded by Teflon to prevent leakage. Make three or four turns in the normal direction of screwing.

Connected irrigation hoses, plates are unrolled

green roof irrigation fitting

The fitting is then screwed onto the collar. Tighten by hand so as not to break this piece: it is a fragile place and it happens that it breaks if we walk on it. Provide some in advance.

check the collars of the irrigation system of a green roof

It should be checked that all the clamps and fittings are fixed in front of the irrigation pipes. If the collars are not quite in front of the pipes, you can play a few centimeters.

irrigation connection for green roof

Once the tips are installed, each irrigation pipe is connected. Just insert the tube on the tip and tighten the locking ring by hand, in the opposite direction of clockwise.

green roof pipe

The last irrigation hose is connected to the collar. The end of the nanny is closed by a plug fitting. In case of problems, this connection allows access to the installation or to purge it.

fix the pipe of a green roof

The other end of the irrigation pipes is plugged to maintain the pressure inside the pipe. After folding the tip, it is surrounded by stainless steel wire and twisted without too much stress.

sedum plate for green roof

The first plate of sedum is unrolled in an angle by adjusting well the sides. The pose then continues, each plate flush with the previous one. The cuts are made by shears. The spaces between the joints and any tears are clogged with fragments of plates. Nature will do its work and all will unify little by little, with a minimum of maintenance.


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