## 3 Case Study, Materials and Methods  
In this paper households' perceptions on energy benefits, living conditions and sociodemographic features are gathered using a questionnaire integrated into the Fotocasa Research Annual Survey. The survey was implemented using a panel of households complemented by actual home seekers coming from Fotocasa property listings that ranks among the largest in the country. The sample was representative in sociodemographic terms of the Spanish population participating in the selling and leasing housing markets in the country. It was applied to people between 18 to 75 years old, rendering a sample error of \(\pm\)1.4%, using an online platform in the first quarter of 2020 (before the National State of Alarm was declared due to the COVID-19 pandemic). After selecting owners that have sold, bought or leased a home as well as tenants that have leased their current home in the last year, the sample analyzed in this paper was made of 6167 households. Using a 1 to 10 linear scale respondents were required to express their agreement level with some affirmations regarding co-benefits associated with energy efficiency, such as: Savings in the electricity and gas bills, improvement of interior comfort and regulation of internal temperature. Deliberately, aspects such as comfort were stated in a broad form so as to allow the introduction of aspects such as air infiltrations, soundproof issues or condensations (largely present in Spanish homes due to improper envelope insulation and lack of correct ventilation [38] as discussed in 2.2). In the same way, respondents were required to respond whether they consider that energy-efficient homes render a larger market price so as to indirectly learn whether they are willing to bid a larger amount for such kind of efficient premises. Furthermore, respondents were asked to respond whether their present home does require specific retrofits in three dimensions: (1) non-energy efficiency retrofits, (2) energy efficiency passive measures and (3) energy efficiency active measures. Non-energy efficiency measures include aspects related to aesthetics, functional and accessibility improvements of homes in kitchens, bathrooms and layouts. It is worth saying that despite any home transformation has energy performance implications, the usual changes introduced in the assessed retrofits largely rely on aesthetics, functionality and accessibility. Energy passive retrofits splits into window and wall insulation and improvement or setting up of sun/wind protections in the form of avnings and foldable window blinds largely present in traditional architecture in Mediterranean homes. It is worth saying that window and wall insulation improvement in Spain is also perceived as a way to deliver larger soundproof standards, in a country where multifamily homes are dominant (implying noise issues coming from other homes and common areas) and compact, diverse and vibrant urban fabrics produce external noise pollution [39]. Energy efficiency measures regarding active systems split into improvement in Heat Ventilation Air Conditioning (HVAC) systems as well as domestic hot water. Thus, actions such as installing or upgrading present systems (e.g., boilers or heat pumps) to reach higher levels of energy efficiency were inquired. Finally, information such as sex, age, net family income level, civil status, zip code, present home tenure and province of residence were inquired. Academic attainment was not researched since in past Adevina studies its relationship with property preferences was weaker in relation to income level. Information gathered from the survey has been complemented with:  
1. Population of the municipality where respondents live (Padron de Pollacion, INE, 2019).