External thermal insulation composite systems (ETICS) – materials, rendering and renovation
Since the mid-1960s, external thermal insulation composite systems (ETICS) have been used to increase the energy efficiency of buildings. They are used for new builds and for renovation projects – with the exception of listed buildings and half-timbered houses, as the ETICS would conceal the historic façade. In addition to polystyrene, numerous other insulating materials can be used. There is also a multitude of options for the final façade design. Not only this, but old systems do not necessarily need to be disposed of immediately but can be doubled up.
Structure and functionality of ETICS systems
ETICS systems involve a multi-layer construction which is applied to the external façade. The individual components are designed to work together: fastening to the supporting wall, heat insulation, the reinforcement layer and the external plaster. The fundamental task of ETICS is the aforementioned heat insulation function. It prevents heat from escaping from a building through the walls. This reduces energy costs, the consumption of fossil fuels and the CO2 emissions.
ETICS is more than polystyrene
Today, more than 90 per cent of buildings have heat insulation made from polystyrene boards (EPS/XPS) which is commonly also referred to as Styrofoam. In addition to this, mineral fibre boards and wood fibre boards are also often used.
In general, insulating materials can be split into two categories: organic and inorganic insulating materials. Within one group, a distinction is made between natural and synthetic materials.
- The category of synthetic inorganic ETICS materials include Aerogel, mineral wool and mineral foam.
- Polystyrene, phenolic resin and polyurethane boards are characterised as synthetic organic insulating materials.
- Natural organic materials include wood fibre, hemp wool or cork boards.
Criteria for the selection of suitable insulating materials
When selecting a suitable external thermal insulation composite system, a series of factors are decisive in determining the extent to which an insulating material is suitable for a particular building, its location and manner of construction as well as its energy-related objectives:
- Thermal conductivity: this indicates how much heat is lost externally through the insulating material.
- Water vapour diffusion resistance factor μ: the higher this value, the less vapour penetrates into the material, which has a positive effect on the energy efficiency.
- Gross density: this describes the ratio between the mass to the volume of the ETICS. Lower density facilitates better insulation. The thickness of the insulating material can be reduced with a higher density.
- Primary energy concentration: this indicates how much energy is required to manufacture an ETIC system from obtaining the raw materials through to the end product.
- Materials class: this determines the flammability properties of a material.
Increasingly stringent insulation standards put the focus on thermal bridges. Initially, thermal bridges sound harmless. Bridges are normally practical and allow us to move between two separate areas thanks to the connection they provide. In construction, a thermal bridge represents a weak spot in the building envelope from an energy perspective. Unlike what the term initially leads us to assume, a thermal bridge does not provide a building with heat. Quite the opposite is in fact the case. What’s worse: a thermal bridge can be the cause of mould formation! Read more.
The metastudy “Thermal insulation materials” conducted by the Munich Forschungsinstituts für Wärmeschutz (FIW – the research institute for thermal protection) provides a comprehensive overview of the characteristics of the various insulation materials. Before a specific ETICS is selected, an expert should check to what degree such a system can actually improve the energy balance sheet of the building.
Numerous fixing options for ETIC systems
Fixing the insulating materials to the supporting wall can take place in a variety of different ways. One option is to fix the ETICS to the wall using a special, customised adhesive. There is also the combination of adhesives and dowels as well as mechanical mounting using tracks. The type which is used depends on the insulating material selected, its weight and the base. For example, it is not permitted to use adhesives with mineral wools. Dowelling must be used for this.
Diverse methods of façade design upon ETICS
Insulated façades do not always have to look the same. Plastering and cladding are two basic options to create the external walls on top of the ETICS. For the first type, plasters based on minerals, silicates, artificial resins or silicon resin are available. They can be applied to all surfaces and grain sizes. Silicate and mineral-based plasters have a limited range of colours, but with the other two alternatives, the colours are almost unlimited. The plaster on the ETICS is either dyed prior to application or it can be subsequently painted using pigments which are tailored to the relevant plaster type. That means that silicate paints are necessary for silicate plasters, for example. There is also just as much scope for different design options with the second version, the cladding. The options range from ceramic surfaces, stone, glass, brick and wood.
Renovating and modernising external thermal insulation composite systems
ETICS made from polystyrene have come under repeated criticism recently, as they are difficult to recycle. It is right that the industry should improve its technologies in order to increase the proportion of EPS waste which is recycled, which is currently 25 per cent. External thermal insulation composite systems are very long-lasting, which is why they can be easily modernised by doubling up.
Post-insulation is worthwhile if renovation of the façade or of the entire building is planned in any case. The additional costs for all measures taken will only increase slightly as a result, as the equipment can for example be used for several work steps. The ETICS is just one element in building renovations for energy reasons. This is why the construction measures can be combined with others, for example the professional installation of heat insulating windows and doors. Here, particular consideration must be given to connection joint seals.
Doubling up becomes necessary when the ageing process starts to take hold on the surfaces of the building components. Depending on the model, this takes between 25 and 50 years. In addition to this, lawmakers regularly increase the requirements for the energy efficiency of buildings. Old ETIC systems are very rarely dismantled. Rather, the old system is integrated into a new external thermal insulation composite system, which is the process of doubling up.
However, not all ETICS can be renovated. The old systems must be made of EPS, mineral wool or mineral wool layers, they must be stable and have a coating of plaster. They must also only be affixed to the wall beneath with adhesives or dowels. Due to building legislation, it is not permitted to double up when using track systems.
Selecting the ETICS: conducting a thorough analysis of the building structure
External thermal insulation composite systems make a significant contribution to increasing the energy efficiency of buildings. Researchers at the Institut Wohnen und Umwelt (Institute of Living and the Environment) in Darmstadt work on the assumption that they reduce energy costs in the long term by 25 to 30 per cent. Numerous materials and surface coatings are available, which permit a high degree of individuality. As every building is unique, an expert should conduct a preliminary examination into which ETICS is most suitable to achieve the energy goals. In this respect, avoiding thermal bridges plays an important role, which we will explain in our study of energetic weak spots in the building envelope.