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Internal insulation is often the only possible solution when improving the thermal performance of solid walls of historic buildings, as many of these have architectural or cultural values. However, as internal insulation is regarded risky from a moisture perspective, guidelines are needed. The paper presents a new set of guidelines that combine written guidelines, a web-based preliminary assessment tool and a website that can be used independently of each other. The website provides simple ways of assessing the building to determine whether internal insulation is feasible in the specific case and what needs to be done before it can be applied. It also describes different failure mechanisms. The website includes links to information (written guidelines), described for different types of users, depending on their level of expertise. The web tool is based on an extensive number of simulations of hygrothermal conditions within a solid wall depending on location, orientation, wall type and thickness, and insulation type and thickness. The web tool determines the risk for mould and algae growth in a probabilistic way and determines heat loss and CO2 emission before and after renovation through 1 m² of the wall. The guidelines, the website and the web tool are developed in RIBuild, a research project funded by the European Commission, running from 2015 to 2020.

Moisture loads due to wind-driven rain can lead to accelerated decay of exposed building facades. Hydrophobic impregnation reduces water absorption of facade materials and is thus presumed to decrease moisture related damages. Hydrophobic impregnation however also lowers the drying speed of the exposed facade, leaving mainly water vapour transfer to take place. This study examines the open porosity and capillary absorption coefficient of impregnated brick samples as well as the effect of hydrophobic impregnation on the vapour permeability of brick and mortar samples. The open porosity was measured with vacuum saturation test, the absorption coefficient was determined by water uptake tests, both done after one month of curing of the impregnated brick samples. The vapour permeability was `derived from cup tests and from drying tests. The resulting open porosity from brick samples indicates that the changes in the overall pore structure are minimal after impregnation. In addition, the absorption coefficient of brick was found to be fairly close to zero, even with low concentrations of active ingredient, and regardless the percentage of silane/siloxane. Our findings support the claim that the hydrophobic impregnation does not influence significantly the water vapour permeability of brick and mortar.

The built environment is accountable for 1/3 of the European energy consumption. Thermal insulation is a key factor affecting the energy performance of buildings. Historic buildings typically were made with solid external walls of brick masonry or natural stone, rarely insulated afterwards. Often the buildings have worth-preserving façades making internal insulation the only feasible technique, however significantly modifying the hygrothermal performance of the façade. The research objective of this paper is to simulate the hygrothermal performance of solid masonry walls in an old Danish hospital that will be internally insulated following the Danish requirement (U-value) for external walls (change of use of buildings) and transformed into dwellings, involving different insulation systems. Heat loss and masonry moisture content level after adding internal insulation and the possible effects of hydrophobization on the moisture content is simulated. Simulations show an increased moisture content in the original wall when adding internal insulation implying an increased risk for moisture-related damage (mould growth, frost damage and interstitial condensation). The results also show that hydrophobic impregnation of the internally insulated facades may be vital in avoiding moisture problems and securing a moisture-safe energy renovation of buildings like the one studied.