Study commissioned by the Vienna Ombuds Office for Environmental Protection
Thermally insulated façades make an important contribution to reducing the energy consumption of buildings and thus to climate protection. Composite thermal insulation systems are often used for this purpose, in which insulation panels are provided with a comparatively thin external plaster.
The thermally insulated exterior surface is only warmed to a small extent by heat from inside the building. The façade surface can therefore remain moist for a long time, especially due to night-time cooling, condensation and precipitation. These conditions encourage the growth of algae and fungi, which can appear as greenish, grey or black discolorations.
Such growth usually does not affect the load-bearing capacity of the façade, but can significantly change its appearance. In order to delay the growth of algae and fungi, façade plasters and coatings are often treated with biocidal active ingredients.
The protective effect of these active ingredients is limited in time. Biocides can be washed out of the façade by precipitation and carried into the soil, sewage system and waterways with the runoff water. Some of the active ingredients used are very toxic to aquatic organisms or have other problematic environmental properties.
On behalf of the Vienna Ombuds Office for Environmental Protection, the Technisches Büro Klade examined the potential effects of façade coatings containing biocides on human health and the environment. Both the properties of the active ingredients used and ways to avoid or reduce their use were considered.
The study particularly addresses the following topics:
- hazardous properties of the biocidal active ingredients used,
- Type and amount of biocides used,
- Encapsulation and controlled release of the active ingredients,
- Leaching from façade coatings and entry into the environment,
- possible stresses during processing and application,
- planning and structural measures to reduce algae and fungal growth,
- Biocide-free thermal insulation composite systems, façade plasters and coatings.
The study shows that the protection of a façade does not solely depend on the chemical treatment of the plaster. During planning, material selection and execution, measures can be taken to reduce the moisture on the façade surface and thus make the growth of algae and fungi more difficult.
The study contains strategy recommendations for planning, tendering, procurement and execution. Their goal is to avoid or at least reduce the routine use of biocidal active ingredients in façade coatings. This is intended to reduce the burden on processors, building users and the environment.