**4. Results**

## *4.1. Building Stock Modelling (BSM) Results*

BSM results illustrate that most of the houses in Orkney are detached houses with a mean gross floor area of 118 m<sup>2</sup> (Appendix D—Figure A4). Only 7.4% of this archetype has an EPC rating of A or B. However, C–F bands are distributed evenly between 23–18%. Semi-detached houses have higher B–D band ratings and account for 85% of the total. The mean gross floor area is 80.5 m2 for this archetype stock. Terraced houses have mainly B–D rating bands with a 73 m2 mean floor area. Flats are not considered in this study as it is the smallest category among the number of houses, and the EPC dataset does not have enough sample to analyse this archetype. EPC rating results show that half of the building stock is built before 1975 and only 6% has an EPC rating of A or B or C. However, this reaches 37% with the houses built after 1975. One-fifth of the housing stock does not have age information in the dataset. However, 82% of this category has a rating of A or B or C. So, it can be assumed that many of these categories comprise either new buildings built with higher energy efficiency standards or well-refurbished houses in the existing housing stock.

Heat losses occurring in the building fabric are calculated by the energy model described in Section 3.2 for different construction types (walls, windows, floor, and roof) to explore the impacts of individual construction elements on fabric heat losses (FHL). Results for four different archetypes (detached, semi-detached, end-terraced, mid-terraced) with three different specifications (unrefurbished, refurbished, new building) are investigated. The results illustrate that walls are the main contributors to FHL overall with 51.9% followed by windows, floor, and roof with 26.9%, 13.3%, and 7.9 respectively (Figure 3). However, windows contribute more to a mid-terraced new building because the area of the exposed wall is smaller, and the wall is highly insulated. The contributions are varies depending on the house specification. The impact of walls and floor reduces when the house becomes more insulated, i.e., the impact of windows increases.

Considering these calculations, Figure 4 shows the energy efficiency categories based on their scores of individual construction components and overall results by different archetypes. The impact of individual construction elements varies in different archetypes and building specifications. Therefore, while calculating the overall efficiency score of the house, the weight of the construction element has been altered based on the results illustrated in Figure 3.

**Figure 4.** Energy efficiency scores for wall, roof, floor, windows and overall, by house archetypes.

The results illustrate that a majority of the houses in Orkney are categorised as refurbished with 49.7% of the total housing stock, followed by unrefurbished and new building categories with 27.6% and 22.7%, respectively. The most unrefurbished housing stock exists in detached and mid-terraced houses with 55.8% and 44.2%. The most efficient construction parts are the roof and walls with 69.1% and 60.8% respectively. The floor is the least efficient category in all archetypes and the highest contribution occurs in detached and mid-terraced archetypes with 66.2% and 51.4%.

After identifying the housing stock condition, the current heating situation of Orkney is explored. The main heating type in Orkney is electric heaters with 45.2% of the total housing stock (Figure 5). It is followed by oil boilers and heat pumps with 36.7% and 9.0%. The remainder is provided by wood, coal, and LPG boilers. The majority of heat pumps are used in the new building category with 7.7%.

**Figure 5.** Proportion of main heating fuel type and the total number of heaters.
