## 1 Introduction
### The Role of Perceived Benefits
* Humidity: As example, Fraunhofer IBP (2016) estimates that 2.2 million Europeans have asthma as a direct result of living in damp or moldy buildings [25]. * Indoor air quality: The survey carried by Universitat de Barcelona-Hospital Clinic (Interstitial Diffuse Lung Disease Programme), shows thorough quantitative and qualitative evidence of the relationship between lung diseases and microorganisms present in air indoors. China provides another case where indoor air pollution is estimated to cause some 1.6 million premature deaths per year [26]. The main conclusion to be drawn from the aforementioned studies is that it is necessary to continue working on studies reporting to users and quantifying their perceptions and concerns in order to understand the co-benefits from the energy performance improvements beyond the environmental impact. It will also be a crucial matter to emphasize the social and economic aspect that can promote on a massive scale these improvements. In that vein, the work of [PERSON] and [PERSON] [27] explores the environmental attitude of buildings' users by means of a survey within the Consensus Lifestyle Survey. These authors find divergent approaches: (1) proactive attitudes showing awareness on environmental emergency and the necessity to act on a small-scale level in order to achieve a global impact \"I'm willing to sacrifice some comfort to save energy\" or \"It's important to use less energy and lower utility use\"; (2) passive attitudes which shows a degree of environmental awareness but as a third party \"Society needs to consume less to protect environment for future generations\"; and (3) attitudes which are against energy concessions considering them as an obstacle for their life quality and possession of goods \"My quality of life will be reduced by decreasing energy use or it takes too much of my time to reduce energy use\". Whether co-benefits are correctly perceived by buildings' users before and after energy retrofits has also been researched. The city council of Santa Coloma de Gramanet (Spain), in the province of Barcelona, implemented a large-scale energy retrofit in a low-income neighborhood, using powers derived from urban law. In this project the city council funded the cost of the retrofit and recovered the investment by means of payments charged to landlords across five years. The improvement consisted of improving insulation both in external walls and roofs of multifamily homes. Surveying residents, [PERSON] et al. [28] tried to explore the perceived co-benefits of such large retrofit. According to their results 62% of respondents had noticed a better indoor temperature as a consequence of higher surface temperature on the walls and less energy exchange through the facades, and also a higher building quality at three levels: Home (30% of respondents believe their home had raised its market value); building (10% of respondents consider that neighbor's relationship had improved); and neighborhood (16% considering a better social environment and 45% believing the area had been dignified). In the same vein, [PERSON] et al. [29] using an instrument-based approach, researched the measurable improvements in the context of the Energy Efficiency Retrofit Action of Homes of Older Adults in Phoenix (the US). The measurements performed showed that energy consumption fell 19% after the energy retrofit, at the same time there was a reduction of interior extreme temperatures. Such improved conditions are compatible with the reported improvement of occupants' health. Despite these positive indicators, this study failed to identify any improvement on users' perceptions. This finding suggests that demographics may play a role in co-benefits perceptions. [PERSON] et al. [30] arrived at divergent conclusions (see Figure 2). Their study was focused on the context of a retrofit implemented in 20 homes in Ireland and it was based on surveys to users regarding the perceived co-benefits.