# NZEB Renovation Definition in a Heating Dominated Climate: Case Study of Poland
## 3 Building Models  
Two reference building models were used to determine the requirements for renovation to the NZEB definition (Figure 1):  
* a one-storey building with an attic (numerical model only); and
* a typical two-storey building with a flat roof (numerical model based on a real existing building).  
These two buildings represent very well the most typical single-family houses in Poland. The first one is a small house with a non-usable or usable attic, build before the 1970s. They were built mostly in the countryside or small cities. The second is a two-storey single-family house with a flat roof and unheated basement, so-called \"cube\", build before the 1988. A report drawn up by the Central Statistical Office [7] shows the age structure of building stock in Poland (Table 6). Buildings built between 1945 and 1988 account for 52% of the total. The vast majority of single-family houses (from this period) have a very high level of demand for final energy and, thus, are key targets for renovation.  
According to a The Buildings Performance Institute Europe (BPIE) report [59], in most of the cases modernization of residential buildings implies only a change of heat source or modernization of the heating system (84% of cases). Such solutions result in only a low reduction of the final energy demand--around 10%--and it is usually a result of essential replacement of an outdated heat source. Complex renovation, with final energy reduction of about 35%, refers only to 7% of cases. Renovations to NZEB levels is limited, achieving 0.5-1.0% of all renovations by 2020. The share of deep renovation will be higher and make up to 10% of total. At the same time about 35% of owners in Poland want to renovate their hoses and about 30% does not see such need [60]. The launching of the Clean Air programme along with the use of ambitious requirements could increase the share of NZEB renovations.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Year of**} & \multirow{2}{*}{**Buildings**} & \multicolumn{2}{c}{**Dwellings**} & \multicolumn{2}{c}{**Primary**} & \multicolumn{1}{c}{**Final (Delivered)**} \\ \cline{2-7}  & & & & & **Energy \({}^{*}\)** & **Energy** \\ \cline{2-7}  & **Thousands** & **\%** & **mln.** & **\%** & **kWh/(m\({}^{2}\)a)** & **kWh/(m\({}^{2}\)a)** \\ \hline before 1918 & 413.30 & 7.71 & 1.21 & 9.01 & \textgreater{}350 & \textgreater{}300 \\
1918–1944 & 828.20 & 15.44 & 1.54 & 11.46 & 300–350 & 260–300 \\
1945–1970 & 1367.50 & 25.50 & 3.71 & 27.62 & 250–300 & 220–260 \\
1971–1978 & 676.50 & 12.61 & 2.16 & 16.08 & 210–250 & 190–220 \\
1979–1988 & 763.50 & 14.24 & 2.20 & 16.38 & 160–210 & 140–190 \\
1989–2002 & 698.40 & 13.02 & 1.52 & 11.31 & 140–180 & 125–160 \\
2003–2010 & 616.02 & 11.48 & 1.09 & 8.14 & 100–150 & 90–120 \\ \hline All & 5,363.42 & 100.0 & 13.43 & 100.0 & & \\ \hline \hline \end{tabular} \({}^{*}\) NOTE: The primary energy indicator concerns the index of non-renewable energy used for heating, ventilation and DHW. The final energy indicator concerns the energy of the demand on the heating and ventilation and DHW.  
\end{table}
Table 6: Age structure and energy demand of Polish building stock in 2010 [7,58].  
Figure 1: Reference single family house: (**a**) one-storey building with an attic (1-S); and (**b**) two-storey building with flat roof (2-S).