Hygrothermal performance of exterior walls covered with aerogel-based insulating rendering

• The hygrothermal performance of walls with aerogel based rendering is examined.
• The rendering is tested on an experimental test-cell under real weather conditions.
• Different thermal insulation configurations are compared.
• Results show that interior insulation systems can cause several moisture problems.
• Adding the rendering reduces significantly or removes the moisture risks.

In this study, we present a recently patented insulating rendering based on silica-aerogels. It is mainly developed for exterior thermal insulation applications. In addition to new buildings, it can be used for retrofitting existing ones since it has a high insulation performance and its application is easy, compatible with the traditional masonry facades, and using the well-known ordinary techniques. The objectives are to examine the hygrothermal performance of walls with this rendering and to compare different thermal insulation configurations. The methodology followed is developing a numerical model, then conducting an experimental set-up on a test-cell having the rendering on its south wall to validate the numerical model under real weather conditions. Different exterior wall structures are examined: no insulation, exterior insulation using this rendering, interior insulation, and interior and exterior insulation. Six assessment criteria are used: assembly water content, drying rate, mold growth, condensation risk, ASHRAE-160 criterion, and heat losses. Results show that interior thermal insulation systems can cause several moisture problems: inability to dry out over the years, condensation risk, etc. Adding the aerogel-based rendering on the exterior surface of the un-insulated or the already internally insulated walls reduces significantly or even removes the moisture risks. Also, it reduces significantly the wall heat losses.