*2.2. Building Descriptions*

The base building was a single-family house (SH), which has previously been used as a type building [33], with two storeys and a heated net area of 180 m2. The studied buildings were split into four age categories, based on their construction year and the building code in effect at the time: SH1 (<1976), SH2 (1976–2002), SH3 (2003–2009), and SH4 (>2010). Each age category has tighter thermal insulation requirements than the previous. The ventilation system for SH1 was natural ventilation and for SH2 it was mechanical exhaust ventilation without heat recovery. SH3 utilized mechanical supply and exhaust ventilation with heat recovery as did SH4, but with a higher heat recovery efficiency. The details of the reference building properties are shown in Table 1.


**Table 1.** Properties of the reference single-family houses [34].

In addition, the buildings were divided according to the main heating system in use in the building: district heating (DH), wood/oil boiler, direct electric heating, or ground-source heat pump (GSHP). The share of different heating systems in the building stock within each building age category is shown in Figure 2.

The domestic hot water (DHW) use profile was based on measured data from Finnish buildings [29] and was normalized to 35 kWh/m<sup>2</sup> per year [35], though distribution losses of 0.5 <sup>W</sup>/m<sup>2</sup> were assumed. While the buildings of different ages had different space heating demands, the DHW demand was the same for all buildings. Lighting and electric appliance profiles were based on measured profiles from 1630 Finnish households [30], and the consumption and internal gains were normalized to 5.3 kWh/m<sup>2</sup> and 15.9 kWh/m<sup>2</sup> per year, for lighting and equipment, respectively, to match the Finnish building code [35].

In total, 75% of the Finnish building stock is located in the Southern and Western Finland (Zones I and II), which is why the building simulation used the TRY2012 Helsinki-Vantaa weather data that describes these regions [36]. The average annual air temperature is 5.6 ◦C with an annual solar insolation of 970 kWh/m<sup>2</sup> on a horizontal surface. The heating degree day value is 3952 Kd (at indoor temperature of 17 ◦C) in this heating dominated climate [37].
