Thermal retrofitting of historic buildings is essential to reducing heat loss in all buildings. Although exterior insulation often is hygrothermally a better solution, internal insulation is the only option in facades worthy of preservation (e.g., solid masonry external walls). However, mold growth has frequently been discovered in buildings with internal insulation at the interface between the insulation and the original wall, while simulations and lab tests show minimum risk, and vice versa. Therefore, real-life testing is required so that the building owners are more likely to accept these measures.This paper presents a case study of an 1837-built typical historic building. The study focuses on the building's top floor, a residential area (commune). Eight different rooms have four different types of internal insulation installed. The performance of the insulation systems was determined by monitoring the interior and exterior climate and the temperature and relative humidity at the intersection of the insulation and the existing wall for 20 months. The risk of mold growth was estimated based on the measurements. In the wall interfaces, the Mold Index indicated that the risk for mold growth is not severe. Hygrothermal simulations for the measured period and ten years were also performed. To increase simulation accuracy, the original exterior masonry bricks underwent laboratory testing to determine their precise material properties. The main outcome from the simulations was that the three vapor-open systems were more susceptible to indoor moisture load changes and had an elevated risk of mold growth, whereas the vapor-tight system was more robust to variation in insulation thickness and internal moisture level changes, and in this case, demonstrated the best performance in respect to moisture safety.

Internal insulation is often the only measure to reduce heat loss for facades that are worth preservation, both from a sustainable and architectural point of view. However, insulation from inside may make the original wall vulnerable for moisture related problems. Recent years, quite a lot of research on moisture safe internal insulation of solid brick masonry walls has been conducted. This study takes up the challenge of transforming the experiences from solid brick masonry walls to facades of modern/industrial era up to 1980's. Brick masonry is still often on the exterior side but combined with concrete or light weight concrete on the interior side with or without a cavity. Hardly any research on this topic has been conducted and therefore this paper introduces some first investigations of the hygrothermal performance of retrofitting above types of facades from inside. The study is conducted as a simulation study, where a number of relevant constructions and insulation systems are analysed. Solid brick masonry is used as reference. The results indicate that internal insulation has a good potential for most masonry facades of modern/industrial era. However, insulating solid concrete facades from inside is only possible under certain circumstances.

The present project investigated the hygrothermal performance and risk of mould growth in solid masonry walls retrofitted internally with three diffusion-open bio-based insulation materials (two loose-fill cellulose and one hemp fibre), installed in test containers with controlled indoor climate. Focus was on bio-based insulation materials, as these are upcoming due to necessary CO2 reductions and because the hygroscopic properties of bio-based materials are different from traditional insulation materials like mineral wool therefore, some manufacturers claim a vapour barrier is unnecessary, even in relatively cold climates. The project was a large experimental study in two reefer containers with reconfigured facades, in which solid masonry walls with embedded wooden elements were constructed. The study focused on the conditions in the masonry/insulation interface and in the embedded wooden elements. The effect of hydrophobization and different indoor moisture loads were also investigated. Moreover, the bio-based insulation systems were compared with a wall insulated with the traditional mineral wool and vapour barrier system. Relative humidity and temperature were measured at several locations in the test walls for 1 year and 9 months. Measurements show that exposed masonry walls retrofitted internally with diffusion-open bio-based insulation materials resulted in unacceptably high moisture levels (>80% RH over longer periods). Lower moisture levels were observed when the internal insulation was combined with hydrophobization against wind-driven rain, but unacceptably high moisture levels still occurred (60%–70% in summer and 95%–100% in winter in the interface). Hydrophobization reduced the moisture levels in the interface and embedded wooden elements only in walls facing southwest, which is the direction with the most wind-driven rain. Mould growth tests showed no growth in the interface in walls insulated with cellulose insulation (mycometer surface value <25). Meanwhile growth was found in all four walls insulated with hemp fibre matts (mycometer surface value >400).

Moisture-safe retrofitting and energy optimization of facades in existing buildings may be challenging, especially for buildings with preservation-worthy or historical facades. Internal insulation changes the hygrothermal conditions of the original wall and may cause several problems, like biological growth and masonry deterioration. This paper explores the use of moisture-adaptive membranes as an additional moisture control measure for safe retrofitting with internal insulation. The results are based on WUFI® Pro simulations. Parameters like minimal and maximal vapour diffusion resistance, relative humidity (RH) range at which the membrane is most diffusion-open and -tight, indoor humidity class, orientation, and insulation type are varied and evaluated with a theoretical mould growth model. Results indicate that the adaptive membrane should already be highly diffusion-open at around 75

Internal insulation is generally considered a risky solution regarding the risk of moisture-induced damage such as mould growth and wood decay, and this might particularly be problematic for half-timbered buildings due to the extensive use of wooden elements in the walls. These would be particularly exposed in the case of internal insulation. This study investigates the hygrothermal performance and the theoretical risk of mould growth in critical locations in half-timbered walls fitted with internal insulation through 2D-dimensional hygrothermal simulations. Several types of insulation systems were investigated, including diffusion-open and diffusion-tight systems. Moreover, the effect of exterior plaster to reduce rain intrusion was investigated. The results showed potentially critical relative humidity levels at several places inside the half-timbered walls, mainly when using diffusion-tight systems. However, the combination with exterior plaster positively affected the hygrothermal performance. The direction of the wall is important, as wind-driven rain influences the performance more than the possibility of drying out inwards.

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 diffusiontight 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.

To investigate the robustness of internal insulation throughout the service-life, this paper describes several practical issues connected to the installation and the performance of different systems in the operation phase. The study was conducted through laboratory and field tests, calibrated numerical simulations, and practical knowledge acquired on-site and from the users. Five issues were studied: 1) Practical problems in the installation were recorded through observations and interviews with craftsmen. This showed that the installation process was relatively easy for most systems and, therefore, robust towards installation. 2) A physical robustness experiment evaluated the robustness of the insulation systems against unintentional hitting. The results of standardized laboratory tests revealed that hemp with lime, and phenolic foam were the most robust systems, and aerogel was the weakest and needed the most repairs. However, no damage was observed on any systems after 5-8 years of daily use. 3) A wet cup test was conducted to test the vapor diffusion resistance of typical wall paint types that may be applied during the system's lifetime. The results were used in simulations to determine the paint's influence on the wall's diffusivity. Wet cup tests showed that both the silicate and acrylic paint are diffusion-open, with the acrylic ones being less open, and it is unlikely that a surface can be made too diffusion-tight by conventional silicate or acrylic paint. 4) Experiments were done regarding the microclimate between the external wall and furniture and paintings. The results indicate that it is a good idea to keep some distance to furniture and decorations from a wall insulated with capillary active insulation system to eliminate increased risk of mold growth. 5) Through inspections and questionnaires, residents were asked about the pros and cons of living with interior insulation. The walls showed no extraordinary signs of wear, and in general, the residents appreciated the better comfort and accepted the downside of having a more fragile wall. The process was made through observations and questionnaires to the craftsmen and the residents, and the results revealed that the installation process was relatively easy for most systems.

Hydrophobization reduces the water absorption by facade materials and is often suggested as an optional measure to reduce the risk of moisture problems in internally insulated facades. Studies regarding hydrophobization have mainly focused on moisture performance and whether the treatment is safe to apply to historic building facades. Little focus has been on how the treatment affects heat loss due to the walls becoming drier. This study investigated the effect of hydrophobization on heat loss for solid masonry walls. The study comprises: field measurements from a large-scale experimental set-up containing solid masonry test walls with and without internal insulation and hydrophobization, and a simulation study. Both studies showed a generally positive effect of the hydrophobic treatment on heat loss, although simulations show a low dependency on the type of insulation system compared with field measurements.

Over the last 10 years there has been an increased focus on how internal insulation of the existing building stock affects the hygrothermal performance of the constructions. This study investigates the hygrothermal performance and risk of mould growth in critical locations in internally insulated solid masonry walls when different types of interior paint treatment are applied. The study comprises two parts: field measurements from a large-scale experimental set-up, and a WUFI® Pro simulation study of the effect of paint treatments on different types of internal insulation systems. The focus is on diffusion-open and capillary active insulation systems (autoclaved aerated concrete and calcium silicate). Test walls were applied either with the recommended diffusion-open paint or a widely used acrylic paint. Measurements indicated that the use of common acrylic wall paint does not affect the hygrothermal conditions in internally insulated solid masonry walls considerably, compared with walls painted with the recommended diffusion-open paint. The simulation study did however indicate that in certain situations the use of acrylic paint would be beneficial, while in others diffusion-open paint was preferred.

The limited documentation of the performance of previous and present building techniques in Greenland confines the basis for optimal design decisions. This study presents hygrothermal data from nine houses in Nuuk and Sisimiut, representing constructions of half-timber, concrete, and cross-laminated timber, all designed with a ventilated air cavity. The temperatures and relative humidity are monitored on the wall's inner side, in the air cavities and on each side of possible implemented wind and vapour membranes. The data are subjected to intercomparisons and compared to simulations from the hygrothermal simulation tool, Delphin. Finally, the measured and simulated data are analysed for the risk of mould growth with the Viitanen model in the free software WUFI Mould Index VTT. It is found that all construction types can function adequately under Greenlandic conditions. It is, however, recommended to be critical when excluding building elements, such as wind barriers, due to the risk of reduced performance of the façade structure. Furthermore, it is found that the mould risk is minimal inside the constructions but to some extent critical in the air cavities; however, the consequences of mould there are limited. Finally, the results are compared to other similar studies.

Determining the optimal insulation thickness is useful for designing zero-emission buildings (ZEB) to minimize the environmental impacts. The energy required to heat buildings in cold climates is relatively high. Substantial reductions in the total energy usage of a building can be achieved by reducing the U-value of the external surfaces. Increasing the insulation thickness reduces the operational CO2 emissions, although simultaneously increases the embodied CO2 emissions from materials. To mitigate climate change, Norway and Denmark are trending towards stricter regulations to limit energy use in buildings. However, these countries have no current regulations in the building codes for limit embodied CO2 emissions from materials. This study analyzes the in-fluence of the energy emission factor and future climate change (scenarios?) on the optimal insulation thickness. We used three independent models for case studies in Greenland and Norway. The differences between the case studies highlight the influence of model parameter choices, such as indoor climate, energy emission factor and material emissions, whereas the similarities may be used to analyze the problem from a broader perspective. The results show that optimal insulation thickness calculations are most valuable for case studies in which the energy emission factor is low. Considering energy emission factors above 25-30 g CO2eq/kWh, operational emissions dominated the calculation results in all case studies.

Due to ever-changing building trends in Greenland, the building sector is under pressure; constantly meeting new challenges, there is hardly any research, and the change happens so fast that only very little is learned from the previous attempts. This caused the ABC project to initiate several real-time experiments, including a Test Pavilion in Nuuk consisting of five different wall constructions oriented towards North and South, to determine if any of the designs were more suitable for Greenland than others. This article presents the measured data from this pavilion. It compares the performance of each construction type with each other as well as to simulations performed in the hygrothermal analysis software Delphin. Furthermore, the robustness of the facades is challenged by performing simulations with modelled weather files for other Greenlandic cities and evaluating the results for mould growth risk in WUFI Mould Index VTT. It is found that the constructions are unevenly affected by orientation. Nevertheless, none of the constructions can be labelled unsuitable for the Arctic climate as the assessments revealed no risk for mould growth. Additionally, modelled weather files, ERA5, can be used to perform hygrothermal simulations.

Abstract A recent Danish project has studied the possibilities of using bio-based materials for interior insulation of solid brick walls, without the use of a vapour barrier. The purpose was to give indications of the possibility to use hygroscopic insulation material in positions as interior insulation, where it is known to be potentially vulnerable to moisture accumulation. Three bio-based thermal insulation materials were investigated: loose-fill cellulose insulation (two variants) and hemp fibre insulation commercially available in Denmark. The hygrothermal performance of the three insulation materials for internal retrofitting purposes was investigated in a large-scale experiment comprising several solid masonry walls. The test walls were built in an outdoor test field north of Copenhagen, and exposed to a controlled indoor climate. The experiments were conducted over 1 year and 9 months where moisture measurements were done in several locations within the walls, including the interface between insulation and masonry, as well as in embedded wooden components such as a beam end and a wall plate. The paper illustrates the results from experiments with or without a hydrophobizing treatment on the exterior surface as causes of moisture content in potentially critical places in the walls. Finally, some results from mould growth determinations are reported. Generally, high levels of moisture content were found in the interior insulation, particularly for non-hydrophobized walls, but critical mould growth conditions were found only in the case of one of the tested materials.

The Greenlandic building sector is under pressure due to ever-changing building trends and a building shortage. Regrettably, there have only been made small efforts to investigate the performance of the existing buildings, and few resources have been dedicated to learning from previous attempts. Consequently, the available information and research are insufficient to ensure the construction of robust and well-functioning buildings. This knowledge gap motivated the ABC project, which had the goal of collecting and sharing information about optimal building practices in Greenland. As a part of the ABC project, this study aimed to determine which building practice is the most suitable for Greenlandic conditions. To this end, several real-time experiments were created, including a test pavilion in Nuuk consisting of five different wall constructions oriented towards north and south. This article presents the measured data from this pavilion. The performance of each construction type was compared with each other and to simulations performed in the hygrothermal analysis software Delphin. Furthermore, the robustness of the facades was tested by performing simulations with weather data for different towns in Greenland, including quantification of mould growth risk using the Viitanen model. It was found that the facades were unevenly affected by orientation. Nevertheless, none of the constructions could be labelled unsuitable for the Arctic climate as the assessments revealed no risk of mould growth. Additionally, reanalysis weather data from ERA5 was found to be suitable for performing hygrothermal simulations. It was also found that Nuuk is a favourable location for future test facilities.

Abstract How big should ventilation openings be in ventilated attics? In Denmark, guidelines describe what is sufficient to remove excess moisture penetrating through the ceiling. These guidelines are based on many years of experience. An important parameter is the tightness of the ceiling. With current regulations for the airtightness of buildings, convection through the ceiling is reduced compared to older buildings. Therefore, it is relevant to review these old rules of thumb and maybe revise them. In this two-year study, tests with different sizes of ventilation openings were conducted in a test house with 18 separate ventilated attics and airtight ceilings. One third of the attics were ventilated according to the guidelines, one third’s ventilation was reduced by one third and the last third had 50 % ventilation of the recommendations. Hourly measurements of temperature and relative humidity in the attics were conducted. Rafters in the attics were tested for mould growth. Six different types of insulation systems were used in the attics (with and without a vapour barrier, different insulation materials, and insulation thickness), therefore, the study also includes these differences. Earlier investigations, with full ventilation in all attics, showed no significant hygrothermal differences between them; consequently, it was assumed that the amount of ventilation would be decisive for the hygrothermal performance. This study follows up on this assumption. Results show little differences between the attics, mainly that having a vapour barrier becomes more important with reduced ventilation, and the insulation thickness and thereby U-value is of less importance. Reducing the requirements for ventilation of attics could be relevant, provided that the ceiling is airtight.

Abstract Reducing the heat loss from European buildings must include thermal retrofitting of the historic buildings. In these cases, where buildings have facades worthy of preservation, internal insulation is the only solution although external insulation is better hygrothermal solution. Inspections in buildings with internal insulation have in multiple cases shown mold growth problems at the intersection between the original wall and the insulation. Thus, there is a need for real-life testing; i.e., raising the level of reality by using professional craftsmen to apply internal insulation to existing buildings inhabited by ordinary users. Building owners are more likely to accept these solutions when they have been tested in reality, and not only in the lab or with simulations, on efficiency, robustness, and moisture safety. In Denmark, the older, worthy-of-preservation, historic buildings are commonly built with solid masonry facades. Consequently, internal insulation might involve hygrothermal risks for the external walls. The present study describes a case study of a typical historic building built in 1837. In specific, the paper focuses on the top (5th) floor of the building, which is a residential area (a commune). On the 5th floor, four different types of insulation materials were installed in eight different rooms. The performance of the four insulation materials was determined by monitoring the temperature and relative humidity at the intersections between the insulation and the existing wall, as well as the indoor and outdoor climate. Results of the measurements of the available period showed that relative humidity is increasing for most of the sensors, with an exception of a few sensors that appear to have decreased values compared to the first month. Furthermore, the risk of mold growth was calculated with the VTT mold growth model based on performed measurements and indicated minimum to non-existent mold growth risk so far.

Increased insulation reduces the energy needed during operations, but this may be less than the energy required for the extra insulation material. If so, there must be an optimal insulation thickness. This paper describes the development of a tool to determine the optimal insulation thickness, including what parameters are decisive, and presents some results along with a discussion of the success criteria and limitations. To make these considerations manageable for regular practitioners, only the transmission heat loss through walls is calculated. Although the tool is universal, Greenland is used as an example, because of its extreme climatic conditions. The tool includes climate change, 10 locations and 8 insulation materials. It focuses on greenhouse gas emissions, considers oil and district heating as heating sources, and evaluates four different climate change scenarios expressed in terms of heating degree days. The system is sensitive to insulation materials with high CO2 emissions and heating sources with high emission factors. This is also the case where climate change has the highest impact on the insulation thickness. Using the basic criterion, emitting a minimum of CO2-eq, the Insulation Thickness Optimizer (ITO), generally identifies higher insulation thicknesses as optimal than are currently seen in practice and in most building regulations.