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The external walls, with a thickness of 42.7 cm and U-value = 0.226 W/m2K, are designed for being massive, creating a high-performance envelope that has low heat losses in winter and high thermal inertia in summer.

Starting from the inside, there is the plaster, painted in a light colour, to allow most of the light to be reflected inside the buildings, increasing the brightness of the rooms. Then there are the blocks in expanded clay, which are composed by a mix of water, sand, gravel, expanded clay and cement: in this way they are comparable to natural stone, making them 100% recyclable. The dimensions of the blocks are 250x200x250 mm, and although they are not load-bearing, their size and weight allow anchoring the insulation and the external wall cladding. These blocks are used in all the perimeter walls of the buildings, while earthen blocks are used for internal partitions.

Thus, after the blocks, there is the coat insulation, which is used along all the perimeter walls. To choose the external walls insulation, the fundamental

1 2 3 4 5 6 7

1. Brick cladding 23 mm

2. Support grid+mineral adhesive and smoothing 6 mm 3. Reinforced plastering with metal grid+adhesive and smoothing 8 mm

4. Insulated anchors for mechanical fastening 5. Hemp insulation panel 100 mm

6. Multi-layered blocks in expanded clay 250x200x250 mm 7. Lime/Mortar plaster with metal grid 20 mm

Fig. 4.63

Assembly, thickness and thermal transmittance of the external walls of the designed buildings.

Thickness 42.7 cm

U-value [W/m2K] 0.226

discriminants were to use a product that combined good performance, ease of installation and high sustainability of the production and disposal process.

Thus, 12 cm hemp panels were chosen, composed of 87% hemp fiber and 13% polyester fiber, without additives, which makes them a biodegradable and ecological product; this type of panels works also well as thermal-acoustic wall insulation system and can be applied on masonry systems, as in this case. Other important features are that this type of insulation is highly transpiring and resistant to humidity, is unassailable by insects and rodents, is resistant to mold and completely recyclable.

This insulation thickness was chosen because after some simulations with the DesignBuilder software, which will be detailed in the next chapter, it has been noted that increasing the insulation thickness on the one hand would have diminish the heating consumption, since more heat would have been maintained in the building, but on the other hand the cooling loads would have increased in the hottest periods. This happens because in the warmer months, together with the high external temperatures, with July having an average temperature of 25 ° C, June and August of 22 ° C, there would be the difficulty of disposing internal heat loads, due to the excessive thermal inertia. The right performance compromise between summer and winter was to use 12 cm thick insulation.

Dimensions 625 x 800 mm

Thickness 12 cm

Thermal conductivity λD= 0,039 W/m K

Density 100 kg/m3

Specific heat 2.3 kJ/kgK

Vapor diffusion resistance μ=3,9

Sound absorption αw= 1,00 (class A)

Reaction to fire (EN 13501-1) Euroclass E Compressive strength at 10% of the

relative deformation CS (10) ≥ 17 kPa

Dimensions 250x200x250 mm

Holing percentage (of the total volume) 22%

Average block weight 10 kg

Density 1000 kg/m3

Average compressive strength fbm 3.5 N/mm2

Specific heat 1 kJ/kgK

Vapor diffusion resistance μ 7.5

Sound insulation Rw 52.9 dB

Fire resistance EI 240 min

Thermal resistance R 1.13 m2K/W

Tab. 4.1.2 Thermal and physical characteris-tics of expanded clay blocks.

Tab. 4.1.3 Thermal and physical characteris-tics of the hemp insulation.

The outermost layer of the assembly is composed by the cladding: onto the hemp insulation there is a reinforced plastering with metal grid joined with an adhesive and smoothing, 8 mm in total; then, there is a support grid on which the mineral adhesive and smoothing is applied, 6 mm in total. After this layer it is positioned the actual external cladding, made of stone bricks, with a thickness of 2.3 cm. The fixing of the insulation-cladding system is possible thanks to the use of screw-insulated thermal dowels, which hook onto the expanded clay blocks; to ensure correct system stability, the dowels have at least 2.5 cm of expansion zone inside the blocks.

The walls, moreover, have an excellent thermal displacement, that is the time difference between the time when the maximum temperature is recorded on the external surface of the structure, and the time when the maximum temperature is recorded on the internal surface of the structure; this element is important for determining summer thermal comfort and, as such, has important repercussions also in terms of energy savings.

During the hottest periods, it’s important to have a thermal displacement of at least 8 hours, but an optimal displacement is around 12-16 hours: in this way the heat will enter the house at night, after 22.00 PM , when it’s possible to use the natural ventilation which can rely on the outside environment with lower temperatures, therefore reducing the cooling need. For the used assembly it was obtained a value of 12 hours of thermal displacement.

The assembly has a good thermal quality, and according to the analysis carried out with DesignBuilder: it emerged that the wall has a good total U-value, equal to 0.226 W/m2K, and it is free of condensation, as can be seen from the graph below in the so called Glaser diagram9 performed for the month in which the worst humidity conditions for the condensation inside the wall can happen, i.e. January.

> Glaser diagram for January

4.9 The Glaser diagram is a graphic method that allows the study of condensation inside a wall comparing the partial vapour pressure value with that of saturation; the formation of condensation in a layer can happen when the partial pressure value is greater than that of the saturation pressure.

Fig. 4.64

Glaser diagram of the external walls for January.