Temperature and moisture evolution beneath an aerogel based rendering applied to a historic building

Retrofitting of buildings defined as cultural heritage with respect to energy consumption and thermal comfort of the occupants is a demanding endeavor due to the additional requirements of the conservation aspect. Within a pilot project an inhabited mill in Sissach/Switzerland whose first mention dates back to the 14th century has been retrofitted by using a highly insulating external rendering containing SiO2 aerogel and mainly mineral admixtures namely hydraulic lime, calcium hydroxide, white cement, aerogel granules, light mineral aggregate, water retaining agent, air-entraining agent, except the organic hydrophobic agent. By a rendering thickness of 5-6 cm, the thermal transmittance through the walls was reduced to one third of its original value and the thermal comfort in the 6 apartments improved substantially including a reduction in mold growth risk. The characteristics of the aerogel based rendering have been discussed especially with respect to preservation aspects. By installing temperature and moisture sensors on the original wall and beneath the insulating rendering it was shown that its application on the original walls fulfils the requirement for avoiding moisture accumulation. Further, hygro-thermic simulations were performed extrapolating temperature evolution and water content for a period of 5 years. The object represents a new paradigm in the energy efficient restoration of the built heritage and simultaneously respecting the conservation aspects. The project has been carefully monitored by the state office (Basel-Landschaft) for preservation of monuments.