Green roof, garden courtyard and bamboo rows

4.6 Technological solutions

Fig. 4.54 (down) ► View of the lateral walkway from the west side of the hostel towards the private house.

Fig. 4.53 (up) ► View of the lateral walkway from the east side of the hostel towards the private house.

But the green roof, in conjunction with the courtyards, has important ecological functions, enclosing within it a good part of the considerations made since the beginning of the project: firstly, thanks to the evapotranspiration of the vegetation it allows to reduce the temperatures inside the project site, excluding the formation of “heat-islands”; therefore thanks to the presence of the plants it allows to reduce the presence of pollutants, retaining fine particles and absorbing CO₂; diversifying the vegetal species of roof and courtyards and using local species as much as possible, it is possible to recreate ecological niches, for the local insects and small birds.

In addition to the roof-courtyard system it is added the bamboo row, which runs around the entire perimeter of the project site, with the exception of the border wall to the south. This design choice was made to improve the vision and the liveability of the side walkways, while also providing a good solution to avoid overheating of the walls in the summer period, choice that, together with the green courtyards and the use of light coloured paving, allows to greatly reduce overheating.

At the same time, the bamboo row forms a continuous green system in the courtyards, like a “sheet” that runs from one border wall to the other the courtyards space: visually the walls are covered by bamboo, then there is a

◄ ^{Fig. 4.55}

View of the internal courtyard of the private house.

◄ ^{Fig. 4.56}

View of the internal courtyard of the hostel.

short interruption due to the walkways, then there are vegetable gardens and plants, then there’s again a small interruption due to the floor, to conclude with the bamboo plants covering the other side wall.

To design the courtyards, the project started by dividing them into longitudinal strips with a width of 0.80 m, thus rationalizing the space and filling the area in front of the buildings, leaving the side passages free.

Then it was designed a simple form that could be integrated into this layout, that is a rectangle of sides 0.8 x 2 meters. Thanks to this design strategy it is possible to dynamize the layout of the courts, that at the same time can be re-formulated and rethought according to the needs of the users: in case of need, the single rectangular units can be moved, or it is possible to zoning the cultivation of particular plants or create areas with aromatic herbs or fruit plants or decorative greenery.

Once this step was completed, three different types of use of rectangular units were defined:

• soil for green of low-medium stem, fruit plant or cultivation

• bamboo wood flooring for walkways

• soil for medium-high decorative or fruit trees

For both green courtyards, in addition to the walkways, rectangular areas have also been designed, also paved in removable bamboo wood, allowing to create external spaces for building users while connecting pedestrian passages at the same time. Even the shape of these areas was designed using multiples of 0.8 m to create visually uniform spaces.

For the greenery maintenance in the project site, regular work is necessary to avoid in particular that the plants ruin structures or parts of the building;

therefore the project requires that the site owners take care of both the green roofs and the courtyards.

An interesting fact refers to a local tradition that occurs once a year, during the Qingming Festival⁷ or Sweeping the tombs festival, that is on 4th/5th April: on this date the whole family meets to look after the family tombs, and to clean the roofs of the buildings of the family courtyard. Therefore this tradition could be used to completely settle the whole area once a year.

4.7 The Qingming, or Ching Ming festival, is a traditional Chinese festival observed by the Han Chinese of China, which usually is on the 15th day after the Spring Equinox.

Fig. 4.57 ►

3D view of the 3 component system of the courtyards: medium-trunk trees, bamboo wood flooring and vegetable garden / lawn.

◄ ^{Fig. 4.58}

3D view of the 3 component system of the green roof: wooden box, bamboo wood flooring and vegetable garden/lawn.

As the courtyards, the green roof has a dual function: on one hand, it represents an added value for buildings by giving space to the green that would otherwise be used for normal flooring or for a normal roof, and on the other, above all, it provides great support as a passive strategy; in relation to the last concept, as well as reducing the temperatures inside the project site and the presence of pollutants, retaining fine particles and absorbing CO₂, excluding the formation of “heat-islands”, and creating ecological niches, the green roofs of buildings designed act as a thermal mass: in winter, thanks to this type of stratigraphy, little heat is lost, while in summer the loads due to solar radiation are prevented from entering the building, thanks to the presence of the green, which partly absorbs and reflects the radiation, and soil. The green roof has a great weight as a passive instrument, as will be highlighted in section 5.7.

For designing the roof stratigraphy it was taken as a reference the regulation UNI 11235⁸. When designing a green roof, there are three main types to choose from, which are: extensive, with shallow soil, about 70 mm, that support sedums, moss herbs and grass and do not include pedestrian access; semi-extensive, with a soil layer of about 150 mm, which allows to plant a wider variety of plants and requires only periodic maintenance and can provide pedestrian access; intensive, that has a soil layer from 150 mm upwardsand allows medium-stemmed plants to rise and allows pedestrian access, but requires a constant level of maintenance.

The green roofs designed in the project are of the intensive type and have a soil layer of 250 mm, which, as mentioned, allows to plant plants of higher height and wider variety.

On a morphological level, the green roof follows the same guidelines as the courtyard, being designed to have a regular division, being divided into rows of the same size; in this way the owner can change the layout according to his needs: the design started from a simple division into longitudinal strips of width 0.80 m, as well as those of the courts, to then combine it with one

4.8 UNI 11235:2015, Instructions for the design, execution, control and maintenance of green roofs

The latters, 20 cm wide, are composed of a steel flange support, covered on the external side by a thin brick veneer, while on the high interior where the green roof is, by a 3 mm steel flashing painted with light paint, as well as the upper edge of the parapet. The height is 1 meter.

Following the instructions for a correct design of the roof drainage, it was planned to install roof outlets at the four corners of the roof, with inspection dwells over each outlet to allow regular inspection and cleaning the vegetation from the outlet grating. Together with this, the stratigraphy of the roof was defined.

Talking about the green roof assembly, as mentioned the outermost layer is the extensive soil mix of 250 mm; the following layer is a filter membrane 0.8 mm thick. Furthermore, the water outflow from a green roof is fundamental, and involves two motions, one for vertical infiltration in the substrate and one for sub-horizontal drainage towards the drains. In this case, a 3 cm thick recycled HDPE drainage board was used, with a compressive strength of 1600 kN/m².

The waterproofing membrane is coupled with the root barrier, and they are both 3 mm thick, and serve to completely block the passage of water and roots to prevent damage to the structure of the building; it is therefore necessary that they are installed properly. In addition they, along the edges of the green roof, go up for a stretch overlapping with the vapour retarder of the parapet, to avoid any kind of water infiltration.

After the two membranes the sand sloped creed, of 5 cm is positioned in the point often seen on the edges, which has an inclination of 1% to allow the water to flow out.

Then there is an insulation panel in wood fiber of 10 cm, which has a high compressive strength and a high insulating power, in conjunction with the fact that it is recyclable like natural wood in case of replacement or removal;

coupled with the soil it has an excellent insulating power.

Then it is positioned a vapour barrier to avoid humidity rising from interior

Fig. 4.59 ►

View of the green courtyard-green roof system of hostel and private house.

simple form, a rectangle of 1 x 2.40 meters. In this case the small rectangular areas are bounded by 20 cm high wooden planks, which lay on the earth layer to increase the overall thickness, in this way a greater soil thickness is obtained in order to plant different varieties of plants. These boxes are arranged transversely compared to the rows.

Then to facilitate access to all parts of the roof, without using too much space for walkways, an 80-cm-wide bamboo-paved pedestrian path was designed, which from the point of arrival of the staircase creates an L, “cutting in two”

the roof: this pathway is the same for all three green roofs. What varies is the common area designed on the roof, which is positioned at the end of the path: for hostel and private house it is similar in size, respectively 18 and 20 m², while for the first building it is not foreseen; in the last case a small rectangular area is positioned in the corner and can be used to lay support tools or work material, since a common space is not necessary. The common areas of hostels and private houses are shaded from solar radiation thanks to the placement of curtains attached to a light metal structure.

First of all, after having finished to design the structure of the building in detail, defining the exact size of the parapets, to understand the effective area of the roof, it was planned to install a 300 mm wide layer of gravel along the entire perimeter inside, bordered by parapets.

Dimensions 1350 x 600 mm

Thickness 10 cm

Thermal conductivity λ_D= 0,046 W/m K

Density 230 kg/m³

Specific heat 2.1 kJ/kgK

Vapor diffusion resistance μ=5

Sound absorption α_w= 1,00 (class A)

Reaction to fire (EN 13501-1) Euroclass E

Compressive resistance 100 kPa

1. Intensive soil mix 250 mm 2. Filter membrane 0.8 mm 3. Drenage system 30 mm 4. Protection fabric 3 mm 5. Root barrier (HDPE) 3 mm 6. Waterproof membrane 3 mm 7. Sand sloped screed (Incl. 1%) 8. Wood fiber insulation panel 100 mm 9. Vapor barrier

10. Wood protection board 30 mm 11. Wood joist 80x160 mm 12. Wood beam 200x350 mm

1 2 3 4 5 6

7 8 9 10 11 12

Thickness 47 cm

U-value [W/m²K] 0.226

◄ ^{Tab. 4.1.1}

Thermal and physical characteristics of the wood fiber insulation.

◄ Fig. 4.60

Assembly, thickness and thermal transmittance of the green roof of the designed buildings.

spaces of the buildings.

Lastly there is the internal wooden structure of the building, which includes a wood protection board of 3 cm, a wooden joist 80x160 mm and wood laminated beams 200x350 mm.

As said, the green roof represents an excellent solution in terms of insulation:

in fact the plants on the roof shade its surface, dampening the incoming thermal load and cooling the air thanks to the evapotranspiration; enough said that green roofs hold and accumulate 50 to 90% of rainwater and return it to the environment through evaporation. In addition, the earth works as thermal mass, increasing the insulating power of the assembly. As detailed in section 5.7, the use of green roof has made it possible to reduce the energy demand, decreasing the heat losses in winter, and heat access in summer due to high solar radiation.

Another advantage is the insulation from an often underestimated pollution, the “electro-smog”: 15 cm of light substrate of a roof garden absorbs more than 90% of the emissions in the frequency range of the mobile cellular network and of the transceivers.

The typical load of this type of green roof is 200-550 kg/m², with an average for accessible green surfaces that can be used in similar constructions, which averages a weight of 350 kg/m²; for this project a weight of 400 kg/m² was taken into account in the worst case of water-saturated soil.

The designed green roof, given the thickness of 25 cm of the soil, if intended for cultivation, is suitable for vegetables and fruit plants, such as salad, onions, aromatic herbs, courgettes, aubergines, squash, cabbage, melon, strawberries .

Thanks to the use of wooden tanks in the roof it was possible to increase this value, being able to use more demanding fruit plants and vegetables:

tomatoes, green beans, raspberries, blackberries, currants and similar plants in fact need a substrate thickness of 28 up to at 40 cm.

In the same way small bushes and small trees with a maximum height of 2-3 meters can be planted.