The pollution of the environment and the waste of natural resources has led in recent years to a shift in conventional construction practice in search of techniques and materials that constitute a more sustainable built environment. It is estimated that the construction sector globally consumes approximately 3 billion tons of raw materials annually, an amount corresponding to 40% of total consumption. In addition, buildings continue to burden the environment even after their construction due to the energy they consume, the emissions they produce and their impact on the soil. Therefore, the shift towards a “greener” architecture based on criteria such as the rational use of raw materials, the environmental footprint of constructions and the safety of users is considered more and more imperative.
Sustainable building is a holistic approach to architecture that promotes positive effects on the environment throughout the life of the building, from design to construction, including the production process of the materials to be used. “Green” materials are those that have a reduced adverse impact on the environment and on the comfort of users, while at the same time improving the energy efficiency of buildings either compared to other materials of the same category or as purely ecological materials. A representative measure of the degree of sustainability of a material is embodied energy, i.e. the sum of its energy requirements from the time of collection of its raw materials, its formation as a product, its transport to the market, its placement in manufacturing, its maintenance during its life cycle up to its end-of-use disposal, breakdown, recycling or reuse.
Criteria for choosing ecological materials
In order to qualify a material as “green”, it must meet certain criteria and depending on the multitude of ecological characteristics it has, it is ranked higher or lower in the environmental assessment systems for materials and buildings, such as LEED, BREEAM, etc. The properties of ” “green” materials are grouped into the following categories:
• Efficient use of raw materials. These are materials that are available locally, saving energy when transporting them to the construction site, materials that are natural and collected from areas, from which their use is certified, materials that are manufactured using methods that limit energy consumption , the emission of greenhouse gases and the generation of waste in relation to other conventional production methods, materials that are recyclable or, finally, recycled materials from demolitions, renovations or repairs, which are used as is or processed.
• Indoor air quality. Materials that protect the health of users are those that have a low or zero content of chlorofluorocarbons (CFCs) and volatile organic compounds (VOCs) according to their manufacturer’s certifications, those that prevent the appearance and accumulation of moisture and mold, those that for their maintenance and cleaning, mild, non-toxic substances are needed, as well as the systems or equipment elements, which locate and remove the pollutants.
• Energy efficiency. These are materials, components or passive and active systems, which contribute to the reduction of energy consumption during the construction and operation of the building.
• Save water. Products and systems that help reduce water consumption in the building and save it in outdoor installations.
• Lifetime. Materials with greater strength and life compared to conventional ones can be applied in a smaller amount and at the same time reduce their repair and replacement requirements.
• Affordable cost. An important parameter of ecological materials is that their cost is competitive compared to conventional materials, allowing their selection within the approved overall budget.
Ecological materials
Indicative “green” materials, which can be used as ecological alternatives to conventional construction materials, are presented below:
• Bearing structure. The vast majority of structures, especially in Greece, are constructed with a reinforced concrete frame. The most important environmental impacts from the widespread use of concrete are the extraction of raw materials, excessive energy consumption during its production, high emissions of CO² and other substances and water pollution related to its production process. In addition to upgrading concrete production technology and replacing the fossil fuels used in it with other sources of energy production, it is possible to produce “greener” concrete by replacing cement with fly ash, silica fume, blast furnace slag or pozzolan, contributing in the reuse of industrial materials, and/or replacing sand and other aggregates with recycled aggregates from excavation, construction and demolition waste, with the predominant ones coming from concrete, ceramic or bituminous materials, plaster or glass. The replacement of the aforementioned components, in addition to reducing the energy footprint of the concrete, often contributes to the improvement of the technical characteristics of the material, its workability and its cost. Correspondingly, the concrete reinforcement can be replaced with recycled steel bars and elements. Another construction practice that enhances the sustainability of a concrete building is the use of precast concrete elements, as in this case it is easier to produce it with energy, material and water savings and without the use of wooden forms, compared to the usual process concreting at the construction site.
Within the context of continuous research and development of materials technology, a variety of new materials and systems have been developed, several of which are distinguished by their reduced energy footprint. One such material that belongs to the category of special concrete and although it is historically one of the first forms of reinforced concrete, is treated as a new material, is ferrocement. It is made from cement mortar with or without the use of aggregates and other additives and improvers, around a metal mesh that acts as reinforcement and creates load-bearing structures of light weight and thickness. It is more environmentally friendly in terms of the energy footprint of its manufacture, as it uses up to 60% less cement and 25% of other materials compared to what is used in a conventional reinforced concrete structure of similar static function.
Another alternative and ecological building material, suitable both for the foundation and for the construction of the walls of a building is Faswall®. These are large building blocks, consisting of 85% small pieces of recycled wood elements and only 15% cement. It is a material with a large thermal mass, it is water-vapour permeable, preventing mold and moisture condensation from water vapor diffusion, it has excellent heat-insulating and sound-insulating behavior, and great ease of application. As it is made from organic and recycled materials, without the addition of chemicals, it is ecological and ensures high quality indoor air.
• Masonry. The most representative materials used in infill masonry are optical bricks and cement bricks. With the criterion of reducing the clay or cement used for their construction and limiting their embodied energy, a variety of eco-bricks have been developed from materials such as fly ash or pulverized reusable materials, especially from waste from the construction sector. Of particular interest are constructions made from alternative masonry systems, such as compacted soil, straw bales, earth bags, straw clay, tree trunks with mud, traditional bricks, etc.
• Insulation. Common thermal insulation materials, such as expanded or extruded polystyrene and polyurethane, have a very high embodied energy and contain ingredients with a controversial ecological character such as benzene, styrene and chlorofluorocarbons. Within the context of the wider trend towards ecological and recycled materials, a number of alternative proposals for natural insulation materials have been developed and widely implemented. Wood wool, perhaps the most well-known ecological insulating material in Greece, consists of wood fibers with cement as a binding material, offers mechanical resistance, thermal insulation, sound insulation and sound absorption, is recyclable, harmless to health, produced without high energy consumption, difficult to burn in in case of fire and does not release toxic substances. Sheep wool insulation, a waterproof material with remarkable hygroscopicity, also has excellent heat-insulating and sound-absorbing performance. Cork is also a waterproof insulating material, which offers thermal insulation, anti-vibration insulation and sound insulation. It is light, very resistant to extreme temperatures and pressure, water-repellent and stable with a long life. Other suggestions of ecological materials with sound-insulating and heat-insulating properties are cellulose insulation made by 80% from recycled newspapers, cotton fiber insulation from recycled fabrics or jeans, insulation from recycled plastic, etc.
• Coatings. The most widely applicable ecological coating is the traditional korasani. It is a colored mortar resulting from the mixing of natural rocks with theraic earth and ceramic powder, it has excellent hydraulic properties, great durability and does not need painting and maintenance.
• Paints. Conventional exterior and interior paints contain substances, such as heavy metals and volatile compounds, which are largely responsible for the “sick building syndrome” due to poor indoor air quality, with consequent consequences for the comfort and health of users. Mild chemistry paints with a low or zero content of volatile organic compounds (VOC) and those that are 100% organic are characterized as ecological. All-natural paints have as raw material vegetable resins and oils, waxes and mineral materials, such as chalk, borax, ocher, which are safe for the user, environmentally friendly, recyclable and biodegradable.
• Floors. One of the most ecological flooring materials, which has been widely used in recent years, is bamboo. As a plant, it grows rapidly and spreads by itself, without the need to replant after harvesting. In addition, as a material it has a high mechanical strength in relation to its weight, which extends its lifespan. With high tensile strength and high compressive strength, it is a material suitable for floors, floor substrates and masonry. Like bamboo, cork is a material which, due to its flexibility, durability and insulating and anti-vibration properties, is an ideal choice as a substrate or as a final floor surface. Regarding wooden floors, it is recommended to use wood certified for the protection of forests or to reuse old boards that have been discarded after renovation or demolition. Other recycled or reused materials that can be used in floors are reusable ceramic tiles, tiles or rolls made from recycled plastic (e.g. from car tyres), carpets made from natural or recycled materials, etc. Finally, linoleum is an interesting “green” material, as it is made of oxidized linoleum with cork and wood filling, on a jute substrate, it is flexible and durable in daily use. Due to the anti-static, anti-bacterial and anti-microbial properties of linoleum floors, they are ideal for places where high hygiene conditions are required, such as hospitals and schools.
Certification of ecological materials
The certification of “green” materials confirms that the certified products meet certain specifications regarding their environmental footprint. The approximately 600 certification bodies worldwide are distinguished among those that classify products based on their life cycle and concern energy consumption, the percentage of recycled material, emissions to the atmosphere and water from the stage of manufacture, use to disposal them and those who focus on individual qualities.
Some of the most representative certifications are the following:
• The European Ecolabel (Ecolabel), which covers a wide range of products and services and its award criteria are not based on a single factor, but on studies that analyze the effects of the product or service on the environment throughout the cycle its life cycle, starting from the export of raw materials, its production, distribution and disposal.
• The Blue Angel, which characterizes environmentally friendly products and services.
• The Seal of Approval of the British Allergy Foundation, which certifies that the products in question have significantly reduced allergens and chemical ingredients. It applies to floors, linings, paints and varnishes.
• FSC and PEFC certifications for wood products, which ensure that the wood used as raw material comes from responsibly managed forests.
• The Energy Star certification for the consumption of electrical office appliances.
• The Eurovent certification for the energy efficiency of air conditioning and cooling systems.