*2.1. Studied Buildings*

### 2.1.1. Selection of Buildings

The selection of buildings was largely based on the data availability. Often the actual building energy use data after renovation were not easy to obtain. Eight projects were used in this study to control the variables of building size, age, building system used, and local climate condition. All eight buildings are located in the same city and were built around similar periods, with the energy retrofits mainly focused on the buildings' heating system and exterior façade. Demonstrated in Figure 1 the eight buildings were part of the "European cities serving as Green Urban Gate towards leadership in sustainable energy" (EU\_GUGLE) project [16]. The project aimed to demonstrate the feasibility of a nearly zero energy building renovation target; it started in 2013 and lasted for six years. Six pilot cities from Italy, Austria, Finland, Denmark, Estonia, and Slovakia participated in the project. Around 200,000 m2 of gross floor area was renovated and targeted primary (source) energy savings of up to 82%. Eight buildings in Tampere, Finland, participated in EU\_GUGLE. All eight buildings are in the Tammela district, a traditional residential district close to the city center and railway station. There is a total of around 299,000 m2 of existing building stock in Tammela district. The current average energy use intensity is 213 kWh/m2, and the target intensity is 160 kWh/m2 [17], around a 25% operating energy reduction.

**Figure 1.** Studied project location map.

#### 2.1.2. Case Building Physical Characteristics

The studied buildings were built between 1961 and 1980; the renovations were completed between 2014 and 2019. Seven buildings have six floors and one has four floors—only the four-story building was built in the first half of the 1960s. All eight buildings selected reflected a typical building constructed in the 1960s and 1970s before building energy regulations were enforced in Finland [18]. According to Niemelä et al., 2017, Finnish multifamily buildings constructed in the first half of the 1960s were normally built on-site with a tile building façade and "bookshelf-type" framework [19]. Beginning in the late 1960s, prefabricated large concrete panels became the main construction type [19]. In fact, all the studied buildings had prefabricated concrete panels. Table 1 shows the main characteristics of the studied buildings—the buildings' initial conditions without any energy performance improvement interventions.


**Table 1.** Physical characteristics of the studied case buildings.
