• Energy Research

An inevitable measure when energy retrofitting historic buildings in Europe, is the reduction of building envelope heat loss. On preservation-worthy facades where external insulation is not an option, installation of internal insulation is gaining pace. The historic buildings in Denmark are often constructed with solid masonry facades and wooden decks. The internal insulation may, however, entail potential hygrothermal risks in walls and embedded wood. Measures such as vapour barriers and capillary active insulation materials are continuously evolving and the subject of much current research. The hygrothermal conditions are of great importance for the durability of the building constructions, and for the health and wellbeing of occupants. Wind-driven rain (WDR) is a central factor contributing to water penetration and moisture loads of the exterior walls. Numerous studies have shown that WDR loads influence the moisture conditions in masonry walls and embedded wooden beams, and can even affect interior relative humidity. In the present paper WDR loads on existing façades in a cold temperate climate were determined by measurements and compared to a semi-empirical model. Simultaneously, the hygrothermal conditions within internally insulated walls with exposed brick and embedded wooden beams were monitored. Furthermore, numerical simulations were implemented for clarification of WDR impact. Hygrothermal simulations and previous studies, inevitably show that high WDR loads result in higher moisture content behind the interior insulation. Results from the field measurements of WDR however, cannot directly be referred to the moisture content measured in walls behind interior insulation or beam ends. However, fluctuations in external air humidity proved to be influential on condiditons in the construction. Implementation of a semi-empirical model for calculations of WDR agreed with previous studies in predictions being too conservative when compared to measured WDR.

Predictions of long term hygrothermal performance can be assessed by dynamic hygrothermal simulations, in which material parameters are crucial input. Material parameters for especially historic materials are often unknown; therefore, there is a need to determine important parameters, and simple ways for estimation of these. A case study of a brick wall was used to create and validate a hygrothermal simulation model; a parameter study with five different parameters was performed on this model to determine decisive parameters. Furthermore, a clustering technique has been proposed to estimate decisive parameters through simple testing of interrelated parameters that are easier to determine.

Internal insulation of external walls is known to create moisture performance challenges due to increased moisture levels and condensation risk on the cold side of the insulation. Capillary active/hydrophilic insulations have been introduced to solve these moisture problems, since they are able to transport liquid moisture to the inner surface and enable it to dry. Experience with this insulation type is rare in Denmark. In hygrothermal 1D computer simulations, several more or less capillary active insulation systems (AAC, calcium silicate, IQ-Therm) in various thicknesses (30-150 mm) have been tested for their hygrothermal performance. The original construction was a 228 mm solid brick masonry wall in a Copenhagen historic dormitory. All simulated systems showed critical relative humidity values above 80% and high risk of mould growth behind the insulation and some also on the interior surface. A moisture safe construction was only achieved when exterior façade impregnation shielding against driving rain was added. The best system showed acceptable relative humidity values both behind the insulation and on the interior surface, a significant increase in minimum temperature on the interior surface, and a reduction of heat loss through the external wall by 85%. The solely application of impregnation also resulted in a moisture safe solution with significant improvements in all parameters and heat loss reduction by 45%. The main conclusion is that capillary active insulation may not be feasible on solid bare masonry walls without additional driving rain protecting especially in case of multi-storey buildings with thin walls in high precipitation areas.

The International Building Physics Toolbox (IBPT) is a software library developed originally for heat, air and moisture system analysis in building physics. The toolbox is constructed as a modular structure of standard building elements, using the graphical programming language Simulink. To enable development of the toolbox, a common modelling platform is defined: a set of unique communication signals, material database and documentation protocol. The IBPT is an open source and available on the Internet. Any user can utilize, expand and develop the contents of the toolbox. This paper presents structure and essence of the library. Potential applications of the toolbox are illustrated through examples.

The objective of this study was to test whether compliance with the current Danish best practice recommendations concerning design of the cold attic space will prevent damaging moisture levels. The project was performed as a full-scale experimental setup in the cool temperate climate of Denmark. The setup comprised 18 north-facing attic spaces with varying ventilation principles and varying infiltration scenarios. The relative humidity and temperature were measured in attic spaces, indoor and outdoor, for almost 3 years. The hygrothermal performance of the attics was evaluated by post-processing and comparing the data with predicted mould growth risk and with visual observations of mould growth. The results showed that following the recommended passive ventilation strategies made the hygrothermal performance in attics with diffusion-open roofing underlay worse. In addition, increasing vapour diffusion tightness of the roofing underlay made the hygrothermal performance of the cold attic spaces under the eaves worse, except for attics with passive ventilation but without infiltration. The hygrothermal performance of the attics with diffusion-tight roofing underlay was poor when combining infiltration and the assessed ventilation strategy. The performance of the same attic without infiltration showed that some degree of ventilation was needed. External roof insulation did not significantly improve the hygrothermal performance of the attic.

Most buildings in Europe were constructed between 1850 and 1960, a period in which energy efficiency was not considered much. However, many of these structures have architecturally valuable facades that should be preserved, making internal thermal insulation the only practical solution. Therefore, internal insulation has grown in popularity despite the potential risk of moisture-related problems behind the insulation and on the external surface of the original wall. To ensure the structure's durability and the residents' wellbeing, insulating solutions must undergo real-life testing to demonstrate their effectiveness and moisture safety. The present paper is a compilation of case studies performed over the last decade in Denmark, it compares across four case studies of residential buildings. The apartments were insulated internally with either diffusion-tight or diffusion open and capillary active insulation systems. In some of the cases, internal insulation was applied in combination with hydrophobization of the existing facade. Temperature and relative humidity were measured in the indoor climate, at the intersection between insulation and masonry, and in some cases also at the wooden beam ends or the spandrels. Additionally, the risk of mold growth was calculated. The current study focuses on the wall's hygrothermal performance in relation to the thickness of the masonry and insulation, the wall's orientation, the indoor moisture excess, the effects of hydrophobization and the role of indoor climate. The results indicate that − while internal insulation of masonry more or less result in expected energy savings − areas with thin masonry or very thick insulation give an increased risk for mold growth. In addition, high indoor moisture excess in combination with diffusion open insulation system increases the risk for mold growth, while the other parameters played a less decisive role. Most buildings in Europe were constructed between 1850 and 1960, a period in which energy efficiency was not considered much. However, many of these structures have architecturally valuable facades that should be preserved, making internal thermal insulation the only practical solution. Therefore, internal insulation has grown in popularity despite the potential risk of moisture-related problems behind the insulation and on the external surface of the original wall. To ensure the structure's durability and the residents' wellbeing, insulating solutions must undergo real-life testing to demonstrate their effectiveness and moisture safety. The present paper is a compilation of case studies performed over the last decade in Denmark, it compares across four case studies of residential buildings. The apartments were insulated internally with either diffusion-tight or diffusion open and capillary active insulation systems. In some of the cases, internal insulation was applied in combination with hydrophobization of the existing facade. Temperature and relative humidity were measured in the indoor climate, at the intersection between insulation and masonry, and in some cases also at the wooden beam ends or the spandrels. Additionally, the risk of mold growth was calculated. The current study focuses on the wall's hygrothermal performance in relation to the thickness of the masonry and insulation, the wall's orientation, the indoor moisture excess, the effects of hydrophobization and the role of indoor climate. The results indicate that − while internal insulation of masonry more or less result in expected energy savings − areas with thin masonry or very thick insulation give an increased risk for mold growth. In addition, high indoor moisture excess in combination with diffusion open insulation system increases the risk for mold growth, while the other parameters played a less decisive role

Prediction of the risk for mould growth is an important parameter for the analysis and design of the hygrothermal performance of building constructions. However, in practice the mould growth does not always follow the predicted behavior described by the mould growth models. This is often explained by uncertainty in the real conditions of exposure. In this study, laboratory experiments were designed to determine mould growth at controlled transient climate compared to growth at constant climate. The experiment included three building materials with four different surface treatments. The samples were inoculated with 8 common indoor moulds. Even after 40 weeks no growth was observed on any sample. The paper describes different hypotheses for the missing growth, and how these have been tested.