Today, the environmental impact of buildings needs to be assessed, not only in reference to the energy consumed by their use but also with regards to the materials with which they are made of. The “Sick Building Syndrome” (SBS) is increasing, meaning that major health issues are linked to chemical contaminants from indoor sources such as building materials, inadequate ventilation, excessive use of heating, as well as ventilation or air conditioning and volatile organic compounds. To remediate this issue, test methods of green building elements, made with giant reed (Arundo donax) and agglomerate cork – which are two typical natural materials of the Mediterranean area – were studied.
Why do we need green buildings?
All over the world, buildings are responsible for approximately 1/3 of the greenhouse gas emission and consume about 40% of resources (United Nations Environment Programme (UNEP, 2016). Unfortunately, pollution of buildings not only refers to the external environment but also the internal one and influences our health and life.
The request for more green building elements are developing all over the world and over the last few years, people are increasingly concerned about the quality of life inside buildings. On the other hand, the “Sick Building Syndrome (SBS) keeps increasing. The insulation building materials have a relevant role in the SBS for the capacity, not only to limit the use of heating, ventilation and air conditioning, but also to limit the emission of pollutants inside a building environment. The disposal of buildings could have another serious impact on the environment, since if building materials become wastes, it is hard to dispose of them. However, when building materials are natural or derived from organic materials, the disposal would not represent a critical source of environmental pollution. Sadly, today most of insulation materials used derive from mineral wool (52% of market share) and plastics (41%), whereas only a small part is natural. It has to be pointed out that the correct use of natural materials as insulation for buildings could give a lot of advantages such as:
• lower energy necessary to produce green building elements
• lower energy to control indoor environmental temperature
• better well-being and comfort for the building’s occupants
• lower impact to the environment during the phases of use and disposal
• CO2 environmental capture
Luckily, an innovative solution for new, green building components was proposed, which improves the performance of Arundo donax L. and cork as well.
The performance of Arundo donax as a green building element
After the earthquake in 1908 in the southern part of Calabria, to take advantage of the light weight of the culms, giant reed was used for cavity walls in the reconstruction of many buildings and refurbishments (Barreca, 2012). In several Countries of Mediterranean areas, giant reed was also used with plaster in some structural elements (floor slabs and roof slabs) until around 1960, especially in rural buildings, but also in some buildings in the city. We can find them in interior elements and also in exteriors under cover (seen below) but always with the cane protected from the water.
Soliman (2009) found out that the mean value of moisture of the plant of giant reed after being cut and naturally dried for 3 months was 12.11% and the mean value for water absorption was 52.6% after immersion in water for 24 hours at room temperature of 23°C. The author measured the mechanical properties of 21 samples of stems and obtained the mean value bending strength of 132,5 N/cm−2 (Newton/square centimetre) a mean value of compressive strength of 67,8 N/cm−2 and a mean value of bearing strength of 27,2 N/cm−2. Moreover, he found that by putting two layers of giant reed with a thickness of 4cm perpendicular to each othe, the best thermal insulation value can be achieved.
The major problem in Mediterranean housing is to insulate the indoor environment from high temperature. To reach this goal, using only high thermal resistance materials is not enough but it is also needed to design and build efficient component solutions to bring out and optimize the thermal properties of the materials.
Barreca and Fichera (2013) proposed a new solution to build thermal efficient wall partitions in Mediterranean areas. Their study analyzed a cavity wall panel made with a wood skeleton on which two double crossed layers of giant reed stems were fixed. The panel was finished on both sides with two layers of cement plaster of 1 cm each. The two double layers of giant reed stems formed an internal air space ofabout 20 cm trough holes located at the top and bottom of the panels. The cavity was then linked to an outside environment to generate an ascendant area flow called “chimney effect”. The authors carried out a steady-state thermal analysis to evaluate the heat transfer through the panel.
To evaluate the energy performances of the innovative walls proposed, a dynamic thermal analysis of a hypothetic one floor Mediterranean house with three different wall solutions was conducted. It was carried out by a building energy simulation program to model energy consumption for heating and cooling the indoor environment of a house (Barreca et al., 2017). The first analysed solution was depicted by the typical Mediterranean brick walls, the second by the proposed walls in agglomerated cork and the third by the proposed walls in giant reed. The hypothetic house analysed was located in Reggio Calabria which is a city in southern Italy.
The analysed house had a regular plan with dimensions of 12×6m on a surface of 72m-2 and a height of 3 m below the roof eaves. The indoor temperature, for the energy performance evaluation, was maintained in a range between 18–25°C. For the three different wall solutions, the result of a monthly energy to heat and cool the indoor environment necessary to maintain the temperature within the fixed range.
The results and conclusion
The total yearly energy demand for heating and cooling the following house was: 4154kWh for brick walls, 1028kWh for agglomerated cork walls and 1807kWh for giant reed walls. The savings are not only economic but also environmental. It was also pointed out that the yearly estimated production of CO2 for heating and cooling the following houses was: 2517kg for brick walls, 623kg for agglomerated cork walls and 1905kg for giant reed walls.
These natural materials have great thermal insulation performance. Their application allows a significant energy saving and consequently lower CO2 emissions in the environment for indoor climate control and for the comfort and health of the occupants. The study concluded that the dynamic thermal analysis carried out for the houses with the proposed walls, highlights a better environmental performance of buildings with agglomerated cork and with giant reed walls rather than brick walls. In fact, the production of CO2 for the indoor environmental thermal control of the house with giant reed walls is less than ½ and for the house with agglomerated cork walls is less than ¼ compared to the brick wall house.
The easy recycling of these natural materials at the end of the life cycle of the buildings does not require much energy or work, and the recycled material could be used in other applications for example for packaging, as a growing medium for plants, mixing it with concrete to enable it to become lighter.
The environmental effects of the disposed wastes are lower than other building materials. The giant reed is a biodegradable material and could be burnt to produce thermal energy. In agriculture cork is a good material to improve the performance of crop soil such as improving air exchange and humidity control.
Thanks to the research, the natural materials could be used in a better way than in the past with the reproposal of traditional architecture principles.
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