3 Energy Efficiency
50. The energy efficiency of a dwelling depends on its physical characteristics. Factors such as the age of construction, the dwelling type, the heating and hot water systems in use and the extent to which the building fabric is insulated, all affect energy efficiency.
51. Based on information about the characteristics of the dwelling collected in the SHCS physical survey, and using standard assumptions about the make-up and the behaviour of the occupying household, the energy consumption associated with the dwelling is modelled. This allows us to make comparisons of energy use, emissions and energy efficiency ratings between dwellings that are independent of occupant behaviour. Further details on the methodology underpinning these measures of energy efficiency are provided in the Methodology Notes.
52. In this chapter we report on analysis of:
- levels of insulation in Scottish dwellings (section 3.1);
- boiler efficiencies (section 3.2);
- Energy Efficiency Ratings (EER), also known as SAP ratings (section 3.3);
- modelled CO2 emissions from dwellings (section 3.5); and
- Environmental Impact Ratings (section 3.6).
3.1 Insulation Measures
53. Installing or upgrading insulation is one of the most effective ways to improve the energy efficiency of a building. The Energy Saving Trust estimates that an un-insulated dwelling loses a third of all its heat through the walls and a further quarter through the roof. As a result, insulation can significantly reduce energy consumption and therefore lower heating bills, making it cheaper to enjoy satisfactory levels of thermal comfort.
54. Additional insulation is most commonly added to a property through the insulation of loft spaces and by adding insulating material to external walls.
- The majority of loft spaces are insulated. In 2017, 94% of dwellings had been installed with loft insulation with a thickness of 100mm or more. This is no change on 2016 but an increase of 12 percentage points on 2010 levels.
- In 2017, 30% of lofts were insulated to a high standard of insulation (300 mm or more). This is similar to 2016 and 2015 following year on year increases from the 2010 figure of 5%.
- The proportion of insulated cavity walls recorded by the SHCS was 75% in 2017, similar to the previous year. In the longer term, the share of insulated cavity walls has been increasing, with a 9 percentage point improvement since 2012.
- The proportion of solid wall dwellings with insulation was 18% in 2017, which was similar to 2016, and an increase of 7 percentage points on the 2012 figure.
- Levels of insulation (both loft and wall) are higher in the social sector than in the private sector. 56% of homes in the private sector have wall insulation compared to 72% in the social sector. In the private sector, 60% of lofts are insulated to 200 mm or more compared to 75% in the social sector; both of these figures are similar to 2016.
3.1.1 Loft Insulation
55. Since 2010, an overall improvement in loft insulation has occurred. The proportion of all housing with 100 mm or more of loft insulation has increased by 12 percentage points on 2010 levels with 94% of applicable dwellings insulated in 2017 (see Table 10), similar to the level in 2016. Most of this improvement occurred before 2013.
56. Figure 9 shows the level of loft insulation in all dwellings back to 2003/4. The share of dwellings with no loft insulation has fallen from 6% in 2003/4 to 1% in 2017. Most of this decline occurred before 2010. Since then improvement has slowed down, suggesting that there may be barriers preventing the installation of insulation in the relatively few remaining lofts.
57. Over the same period the thickness of loft insulation has increased significantly. In 2017, 63% of dwellings with lofts had insulation with a depth of 200 mm or more (excluding properties with no loft). Much of this increase has occurred between 2009 and 2013; when the percentage increased from 27% to 62%. This can largely be attributed to the installation of top-up insulation. In 2017, 37% of lofts had less than 200 mm of insulation, or no insulation, which equates to around 673,000 dwellings (Table 9). The increase in the estimated number of dwellings with loft insulation between 100-199 mm between 2016 and 2017, and the associated decrease with 200+ mm over the same time period, are both within the margin of error of the survey.
58. The percentage of lofts with a high standard of insulation (300 mm or more) has remained similar to 2015 and 2016, at 30%, following significant increases from 5% in 2010 (the first year the SHCS captured this information). In 2017, 28% of private sector dwellings had a high standard of loft insulation, compared to 37% of dwellings in the social sector; both of these figures are similar to 2016.
Figure 9: Depth of Loft Insulation (where applicable) 2003/04 – 2017
Note: A dwelling is classified as ‘not applicable’ for loft insulation if it has a flat roof or another dwelling above it (i.e. it is a mid- or ground-floor flat).
59. Between April 2008 and December 2012, the UK government Carbon Emissions Reduction Target (CERT) scheme delivered 410,937 loft insulation measures in Scotland.
60. Between January 2013 and December 2017 a further 59,359 loft insulation measures were delivered in Scotland by its successor scheme, the Energy Company Obligation (ECO).
61. In total, around 470,000 loft insulation measures have been installed under these government programs since 2008.
Table 9: Depth of Loft Insulation (000s), 2010 and 2012 to 2017
|200mm or more||1,152||1,197||1,161||1,123||1,118||975||621|
|Cumulative recorded loft insulations under government schemes (since April 2008)|
62. As shown in Table 10 thickness of loft insulation is greater in social sector dwellings than private sector dwellings. In 2017, 93% of private housing lofts were insulated to 100 mm or more and 60% to at least 200 mm. In the social sector, 97% of dwellings had lofts insulated to 100 mm or more, and 75% had at least 200 mm of loft insulation.
63. One of the reasons for this difference between private and social sector is that the Scottish Housing Quality Standard (SHQS), which was introduced in 2004, requires at least 100 mm of loft insulation (see section 6.2.2 for more information).
64. The difference in the proportion of lofts with at least 100 mm insulation between the private and the social sector has been reducing gradually, from 17 percentage points in 2003/04 (81% in the social and 64% in the private sector) to 4 percentage points in 2017 (97% in the social sector and 93% in the private sector).
Table 10: Depth of Loft Insulation (000s and %) by Tenure, 2016 and 2017
|Private Sector||Social Sector||All Tenures|
|1mm - 99mm||92||6%||9||3%||101||6%|
|100mm - 199mm||480||33%||83||22%||563||31%|
|200mm - 299mm||459||32%||142||38%||601||33%|
|300mm or more||415||28%||136||37%||551||30%|
|1mm - 99mm||96||7%||13||3%||109||6%|
|100mm - 199mm||451||31%||74||19%||525||29%|
|200mm - 299mm||477||33%||166||43%||643||35%|
|300mm or more||421||29%||133||35%||555||30%|
3.1.2 Wall Insulation
65. The presence of cavity wall insulation (CWI) is becoming increasingly difficult for SHCS surveyors to identify as over time the injection holes age, fade or are covered up by later work. Contractors are also getting better at disguising their work. This may mean that the SHCS under-estimates the number of homes which have had CWI installed (see also section 6.2.2). Despite efforts to maintain the high quality of the SHCS physical survey fieldwork, some misclassifications may remain.
66. In Scotland around three quarters of dwellings have external cavity walls and the remaining one quarter have solid or other construction types of external wall. These “other” types include steel or timber-frame dwellings and dwellings made from pre-fabricated concrete. Because the improvement of solid and other wall types generally requires more expensive interventions than CWI, this diverse group is addressed together in this chapter.
67. Table 11 and Table 12 show the number and proportion of insulated dwellings by type of external wall. Higher insulation levels in new buildings have been required by building standards since 1982. These dwellings are therefore presumed insulated when built.
Table 11: Cavity Wall Insulation, 2012 and 2014 to 2017
|Cumulative reduction in SHCS uninsulated since 2007|
|Cumulative recorded cavity wall insulations under government schemes since 2007|
68. In 2017, 75% of cavity wall dwellings in Scotland were insulated (Table 11), similar to 2016. We know from administrative data that 9,103 cavity wall dwellings were insulated during 2017 (through ECO). However, although the percentage of insulated cavity wall dwellings identified through the SHCS appears to have increased, this is not a statistically significant difference and reflects that this is a sample of all dwellings.
69. The longer term trend, showing a decrease in the share of uninsulated cavity walls of 9 percentage points since 2012, is broadly consistent with administrative data on the number of cavity wall insulation measures installed under the CERT and ECO schemes.
70. Between April 2008 and December 2012, the CERT scheme delivered around 218,000 cavity and 9,000 solid and other wall insulation measures in Scotland. Between January 2013 and December 2017 a further 90,816 cavity and 50,420 solid wall insulation measures were delivered in Scotland by the successor ECO scheme. This equates to around 368,000 wall insulation measures, including around 309,000 cavity wall insulation measures, installed under these programs by the end of 2017. This is clearly reflected in the cumulative reduction of 359,000 uninsulated cavity wall dwellings reported by the SHCS since 2007 (Table 11).
71. Table 12 shows the levels of insulation in dwellings with solid or other construction type walls recorded by the survey in 2017. The results show that 18% of dwellings in this category had insulated walls in 2017; the difference with the level recorded in the previous year (15%) is not statistically significant but is an increase of 7 percentage points from 2012. Only 718 dwellings with solid walls were surveyed in 2017 as part of the SHCS. This relatively small sample does not allow enough precision to capture the increase in solid wall insulation measures which we know from administrative data is taking place. Since the beginning of January 2013 at least 50,420 solid wall insulation measures were delivered in Scotland.
72. In the social sector, around three quarters (77%) of cavity wall dwellings and around two-fifths (44%) of dwellings with solid and other wall types were estimated to have insulation in 2017 (Table 13). Nearly three-quarters (72%) of social housing overall had insulated walls.
73. In the private sector, nearly three quarters (74%) of cavity wall dwellings and more than one tenth (13%) of solid and other wall dwellings, had insulation in 2017. Over half (56%) of all private sector dwellings had insulated walls.
Table 12: Wall Insulation of Solid and Other Wall Types, 2012 and 2014 to 2017
|Cumulative recorded EWI installations under government schemes since 2007, thousands|
74. The information in Table 13 is broken down by type of cavity wall into hard to treat cavities (HTTC) and standard cavity walls using the ECO definition as far as possible with the available data (further details are available in section 7.9.6). HTTCs have certain attributes which make CWI more expensive, complex or inadvisable. Standard cavity walls have no such barriers.
75. 38% of cavity wall dwellings in Scotland have had retrofit cavity wall insulation, which is generally the lowest cost improvement available; the remainder of insulated cavity walls were insulated as built or insulated in another way.
76. Levels of insulation are higher in the social sector at 72% (all wall types) compared with 56% in the private sector. Within wall type, this tenure divide is also apparent for the more expensive insulation measures: internal / external insulation of cavity walls (15% of cavity wall dwellings in the social sector; 3% of private dwellings) and retrofit solid wall insulation measures (44% of solid wall dwellings in the social sector; 11% in the private sector).
77. No statistically significant improvement in wall insulation levels were recorded in the survey in the last year for either the private or the social housing sector. Low sample numbers mean the apparent increase from 2016 in wall insulation amongst households in the social sector and the private sector are within the margin of error for the survey, however improvements have been seen since 2015, when 66% of social sector and 52% of private sector dwellings had insulated walls.
Table 13: Insulation by Wall Type and Tenure, 2017 and Insulation of all Wall Types by Tenure, 2016 and 2017
|Wall and Insulation Type||Private Sector||Social Sector||Total|
|- As built||447||35%||24%||113||21%||18%||559||31%||23%|
|- As built||14||2%||1%||*||*||*||14||2%||1%|
|All Wall Types|
|2016: All Wall Types|
In 2017, 57% of gas and oil boilers meet the minimum efficiencies specified by current Building Standards, an increase of 5 percentage points from 2016.
78. The heating system is a key factor in the thermal efficiency of a dwelling. Around 85% of households use a gas or oil-fuelled boiler. Trends in boiler efficiency are closely related to developments in energy efficiency and building standards regulations:
- From 1998, minimum boiler efficiency standards were set by European Council Directive 92/42/EEC
- In 2007, Scottish Building Standards increased the efficiency requirements for all new and replacement boilers
79. Building regulations in Scotland effectively require the installation of a condensing boiler for gas and oil-fuelled heating in new builds or when boilers are replaced in any dwelling.
80. The SHCS has recorded the age of the household’s heating system since 2010 and contains sufficient data to derive the Seasonal Efficiency (SEDBUK) ratings of surveyed boilers in the 2012-2017 data collections. For these years we can track the energy efficiency improvement of gas and oil boilers associated with the rising standards of the regulatory framework.
81. The methodology by which boiler efficiency ratings are calculated changed in 2016 and the time series was updated at that point to reflect this and to account for the minimum efficiency required of new oil combination condensing boilers. The data presented in Table 14 on the percentage of boilers compliant with standards is therefore comparable with the 2016 Key Findings report but will not match data published in previous reports. Further details on the methodology change can be found in section 7.7.
82. The minimum requirements applied in the assessment of whether a boiler is compliant with standards are: a minimum efficiency of 88% for condensing standard gas, oil and LPG boilers; for condensing combination boilers, 86% for oil, and 88% gas and LPG; for ranges, back boiler and CPSUs, 75% when gas, and 80% when oil.
Table 14: Gas and Oil Boiler Improvements, 2007, 2010 & 2013-2017
|Households using gas or oil boilers for heating||2017||2016||2015||2014||2013||2010||2007|
|… of which|
|% "New" boilers (post-1998)||91%||91%||89%||85%||83%||70%|
|% condensing boilers||67%||61%||56%||48%||43%||22%||7%|
|% standards compliant boilers||57%||52%||47%||41%||33%|
|Sample size (gas/oil boilers)||2,475||2,356||2,259||2,195||2,219||2,488||2,410|
83. In 2017 the survey found that 91% of the domestic gas and oil boilers in Scotland had been installed since 1998, when the European Boiler Efficiency Directive minimum standards came into effect. The proportion installed since then has increased by 21 percentage points since 2010.
84. In 2017, two-thirds (67%) of gas and oil boilers were condensing boilers. This represents a rapid increase of 45 percentage points since 2010.
85. In 2017, 57% of gas and oil boilers meet the minimum efficiencies specified by current Building Standards, an increase of 5 percentage points from 2016. As older boilers reach the end of their life and are replaced, we expect to see a continuation of this trend of improving efficiency.
3.3 Energy Performance Certificates
- In 2017, 42% of Scottish homes were rated as EPC band C or better under SAP 2012, up from 39% in 2016 and from 35% in 2014 (the first year in which data based on SAP 2012 is available).
- Under SAP 2009, which allows comparisons over a longer period, well over two fifths of dwellings (46%) were rated C or better, up 22 percentage points since 2010. In the same period, the proportion of properties in the lowest EPC bands (E, F or G) has more than halved, reducing from 27% in 2010 to 13% in 2017.
86. Energy Performance Certificates (EPC) were introduced in January 2009 under the requirements of the EU Energy Performance Building Directive (EPBD). They provide energy efficiency and environmental impact ratings for buildings based on standardized usage. EPCs are required when a property is either sold or rented to a new tenant.
87. EPCs are generated through the use of a standard calculation methodology, known as Standard Assessment Procedure (SAP). SAP is the UK Government approved way of assessing the energy performance of a dwelling, taking into account the energy needed for space and water heating, ventilation and lighting and, where relevant, energy generated by renewables.
88. The Energy Efficiency Rating (EER) is expressed on a scale of 1-100 where a dwelling with a rating of 1 will have very poor energy efficiency and high fuel bills, while 100 represents very high energy efficiency and low fuel bills. Ratings can exceed 100 where the dwelling generates more energy than it uses.
89. Ratings are adjusted for floor area so that they are essentially independent of dwelling size for a given built form.
90. For Energy Performance Certificates EERs are presented over 7 bands, labelled A to G. Band A represents low energy cost and high energy efficiency, while band G denotes high energy cost (and low energy efficiency).
91. Energy Efficiency Ratings reported in this publication are calculated under two versions of SAP, the SAP 2009 methodology and the most recent SAP 2012 methodology. Using SAP 2009 enables us to examine the trend in the energy efficiency of the housing stock since 2010. SAP 2012 was first used in reporting data from the SHCS in the 2014 Key Findings report and therefore only four years of data are available.
3.3.1 Energy Efficiency Rating, SAP 2009
92. Table 15 shows the trend in mean EERs based on SAP 2009, which rose from 59.9 in 2010 to 65.6 in 2017. These ratings fall into band D. There was around a 1 point increase in the mean EER each year between 2010 and 2014. Improvement since then has been slower, and the increase between 2016 and 2017 was less than 1% which is not statistically significant.
Table 15: Average EER for 2010 – 2017, SAP 2009
93. The median EE Rating has also improved over this period. In 2017 half of all Scottish dwellings were rated 68 or better, an increase from 62 in 2010.
Figure 10: Median EER relative to EPC bands, SAP 2009, 2010-2017
94. The average figures reflect that Scottish housing is gradually moving up through the EPC bands (where A is the most energy efficient), as shown in Figure 11 and Table 16.
Figure 11: Distribution of the Scottish Housing Stock by EPC Band, SAP 2009, 2011-2017
Note: Values for this figure are provided in Table 16.
95. Over two-fifths (46%) of the housing stock in 2017 had an EPC rating of C or better, up 22 points since 2010 (Table 16). Over the period 2010-2017, the proportion of properties in the lowest EPC bands, E, F and G, has dropped 14 percentage points: 27% of properties were rated E, F or G in 2010 compared with 13% in 2017.
Table 16: Distribution of the Scottish Housing Stock by EPC Band, SAP 2009, 2010 and 2013 to 2017
No A-rated properties were sampled between 2010 and 2017.
3.3.2 Energy Efficiency Rating, SAP 2012
96. This section examines the energy efficiency profile of the Scottish housing stock in 2017 under the most recent SAP 2012 methodology.
97. SAP is periodically reviewed by the UK government to ensure it remains fit for purpose and to address application across an increasing range of carbon and energy reduction policy areas. SAP is used for assessment of new buildings whilst a ‘reduced data’ version of the methodology, RdSAP, is applied to assessment of existing buildings.
98. SHCS energy modelling for SAP 2012 is currently based on RdSAP (version 9.92) which was released on 7 December 2014. This introduced some technical updates and broadening of scope (for example, enabling assessment of ‘park homes’ as a dwelling type) as well as updating UK carbon factors and fuel costs based upon recent research undertaken by BEIS. The latest version of RdSAP (version 9.93) was released on 19 November 2017. It has not been applied in this publication since it was not applicable to the majority of the 2017 SHCS sample.
99. Dwellings with main heating fuels other than mains gas (for example oil or coal) have systematically lower SAP ratings in SAP 2012 than in SAP 2009 and this is particularly true at the lower end of the SAP range. The main reason for this is that between SAP versions 2009 and 2012, fuel prices for these fuels increased more than for mains gas. As a result, average energy efficiency ratings tend to be slightly lower under SAP 2012 compared to SAP 2009.
100. Tables 17 and 18 show the energy efficiency profile of the Scottish housing stock between 2014 and 2017 under SAP 2012. Figure 12 shows this alongside the longer term change as measured by SAP 2009.
Table 17: Average EER for 2014-2017, SAP 2012
101. In 2017, the mean energy efficiency rating of the Scottish housing stock under SAP 2012 was 64.3 and the median was 67 points, indicating that half of the housing stock has an energy efficiency rating of 67 or better. The difference in mean rating between 2016 and 2017 was not significant. However, there has been an overall improvement since 2014.
102. More than two-fifths (42%) of all properties in 2017 were rated C or better, an increase from 39% in 2016 and 35% in 2014. Less than a fifth (16%) were in bands E, F or G – a drop of 5 percentage points over the 4-year period from 2014 to 2017.
Table 18: Distribution of the Scottish Housing Stock by EPC Band, 2014 – 2016, SAP 2012
No A-rated properties were sampled for 2014-2017
103. Figure 12 shows EPC bandings for SAP 2009 and SAP 2012. The chart shows a strong trend of improvement in the energy efficiency profile of the housing stock since 2010. The proportion of dwellings rated C or better increased from 24% in 2010 to 46% in 2017 (as measured under SAP 2009), and 35% in 2014 to 42% in 2017 (as measured under SAP 2012).
Figure 12: Grouped EPC Bands under SAP 2009 and SAP 2012, 2010-2017
104. Table 19 shows the energy efficiency profile by broad tenure groups in 2017 using SAP 2012. Figure 13 provides more details on the distribution of the least energy efficient properties by household characteristics.
Table 19: EPC Band by Broad Tenure in 2017, SAP 2012
|EPC Band||Owner occupied||Private rented||Social sector||All Tenures|
105. Over half (55%) of social housing is in band C or better under SAP 2012, compared to just under two-fifths (39%) in the private rented sector and 38% of owner-occupied households. Seven per cent of dwellings in the social sector are within EPC bands E, F or G, while 18% of owner occupied dwellings and 24% of the private rented sector are within these EPC bands. Housing in the social sector tends to be more energy efficient than the owner occupied or private rented sector. This could be driven by the Scottish Housing Quality Standard and the Energy Efficiency Standard for Social Housing which introduced minimum energy efficiency levels for that sector.
106. Figure 13 shows that the share of dwellings in the lowest energy efficiency bands (F and G) is particularly high for pre-1919 dwellings (14%), non-gas heated properties (between 15% and 25%), detached properties (10%) and in the private rented stock (10%). Across Scotland as a whole in 2017, 5% of properties were in bands F or G.
Figure 13: Proportion of Homes in Band F or G by Dwelling Age, Primary Heating Fuel, Tenure and Household and Dwelling Type in 2017 (SAP 2012)
Base figures and more detailed breakdowns are provided in Table 20 and Table 21.
107. More detailed breakdowns are shown in Table 20 by household characteristics. Mean SAP 2012 ratings range from 61.6 in the private rented sector to 69.7 in housing association dwellings, and this is a statistically significant difference. Social housing as a whole is more energy efficient than the private sector, with a mean EER of 67.8 compared to 63.0 for private dwellings.
Table 20: Mean EER and Broad EPC Band, by Household Characteristics in 2017, SAP 2012
|Tenure||EE Rating||Differences from 20161||Band||Sample|
|Weekly Household Income|
|Council Tax Band|
|Band G & H||63.4||41%||53%||5%||187|
Notes: 1. Differences provided where statistically significant.
108. Table 21 shows that there is a strong association between dwelling characteristics and energy efficiency rating. Across dwelling types, detached properties have the lowest energy efficiency profile on average (mean EER 60.7) while flats have the highest rating (68.9 for tenements and 67.0 for other flats).
109. The oldest, pre-1919, properties are least energy efficient (mean EER of 55.6 and only 17% rated C or better) while those built after 1982 have the highest energy efficiency ratings (mean EER of 71.6, with 74% in band C or better). The other age categories are comparable in terms of their energy efficiency profile.
110. Primary heating fuel is a key determinant of the energy efficiency of the dwelling. Properties heated by mains gas have an average rating of 66.8 and 47% are in band C or better. Dwellings heated by other fuels (including electric and oil) have considerably lower ratings. The average energy efficiency rating for oil heated properties is 50.2 (making the average dwelling in this group E rated) and only 9% are in band C or better. Proximity to the gas grid has a similar effect on the energy efficiency rating (average SAP rating 65.7 for dwellings near the gas grid, higher than the 57.5 for other dwellings). As dwelling characteristics associated with lower energy efficiency are disproportionately represented in rural areas, the average energy efficiency profile of rural properties is lower than that for urban; table 21 shows that mean SAP 2012 rating is 66.1 for dwellings in urban areas, higher than the 54.9 for dwellings in rural areas .
111. Improvements since 2016 which pass the statistical significance test include a 1.3 points gain in the mean SAP score for 1945-1964 dwellings, a 0.9 gain for dwellings with gas a primary heating fuel, and a 0.6 gain for urban dwellings. These improvements are reflected by increases in the proportion of dwellings rated band B or C between 2016 and 2017, which were 6 points for 1945-1964 dwellings, 4 points for dwellings with gas as a primary fuel, and 3 points for urban dwellings. Improvements in the mean SAP score between 2016 and 2017 were also seen for tenement flats, however the corresponding increase of B and C rated dwellings for these categories was within the margin of error. Improvements in the proportion rated C or better were also seen for post-1982 dwellings (increasing by 5 percentage points) and those off the gas grid (increasing by 6 percentage points) although the corresponding change in mean SAP score was not significant.
Table 21: SAP 2012: Mean EER, Differences from 2016 and Broad EPC Band, by Dwelling Characteristics, 2017
|Mean||Differences from 20161||BC||DE||FG|
|Age of dwelling|
|Primary Heating Fuel|
1 Differences provided where statistically significant.
3.4 National Home Energy Ratings (NHER)
112. The National Home Energy Ratings (NHER) system was the main methodology used in the SHCS to report on the energy efficiency of the housing stock prior to 2013. With the publication of the 2013 SHCS Key Findings Report the energy modelling methodology was updated and it is no longer possible to reproduce exactly the original NHER method, as the full documentation of this method is not publicly available. However because of user interest and because NHER scores are taken into account under the energy efficiency criterion of the SHQS, we provide an approximate NHER score. Further details can be found in the Methodology Notes to the 2013 SHCS report.
113. Table 22 presents banded NHER scores and mean values for selected categories of dwellings and household types for 2017. Significant differences were seen by age of dwelling, with older dwellings having lower average values (6.4 for pre-1919) than properties that were built more recently (8.7 for post-1982). Private sector dwellings had significantly lower NHER scores (7.4) than social sector (8.1) with mean scores by detailed tenure ranging from 7.2 (owned outright and private rented) to 8.4 (housing associations). There were also differences by dwelling type ranging from detached properties at 7.0 to tenements at 8.4. Dwellings using oil as their main fuel had the lowest score at 5.9 while those fuelled by gas had the highest at 7.9.
114. Table 22 also shows the percentage of homes in each dwelling and household category that were rated as good, moderate, or poor. Significant differences in the percentage of dwellings that were rated as “good” were seen by type of dwelling (66% of detached properties, compared to 85% of tenement flats). A very strong relationship was seen between age of dwelling and the proportion of dwellings rated as good (50% of pre-1919 dwelling, lower than 92% of post-1982 dwellings). Primary heating fuel also had an impact on the proportion that were rated as good (83% of dwellings with gas as a primary fuel, compared to just 40% of dwellings with oil as a primary fuel). This profile is similar to SAP 2012.
Table 22: NHER Scores and Banded Ratings by Selected Dwelling and Household Characteristics, 2017
|Dwelling Type (grouped)|
|Age of dwelling|
|Primary Heating Fuel|
|Other fuel type||6.9||58%||29%||13%||92|
3.5 Carbon Emissions
- Based on modelled energy use, the average Scottish home is estimated to produce 7.0 tonnes of CO2 per year in 2017, which is almost double the average carbon emissions per household as reported by BEIS (3.8 tonnes per year) in 2016. This suggests that households are not heating their homes to the standard heating regimes.
- Average modelled carbon emissions for all properties have continued to decrease in the past year from 76 kg per square metre of floor area in 2016, to 74 kg per square metre in 2017.
115. Carbon Emissions are the amount of carbon dioxide gas vented to the atmosphere. Estimates of emissions from the residential sector which take into account actual energy consumption by households are reported by BEIS at Local Authority and Scotland level annually. This methodology is consistent with the Greenhouse Gas Inventory (GHGI) which is the source for monitoring progress against the Scottish Government’s climate change commitments.
116. In contrast, emissions reported from the SHCS are modelled on the assumption of a standard pattern of domestic energy consumption and do not reflect differences in consumption behaviour due to preferences or changes in weather conditions. As such, they are distinct from the carbon emissions figures published by BEIS and compiled in GHG inventories. Table 23 shows modelled emissions from the SHCS and provides a comparison with the estimates published by BEIS for the period 2010-2016.
117. Average carbon emissions per household decreased in 2011, accompanied by a decrease in the SHCS based average modelled emissions. In 2012, cooler temperatures led to an increase in domestic energy consumption and an increase in CO2 emissions from the domestic sector overall. This was reflected in the estimates of emissions levels from the domestic sector reported by BEIS. At the same time, modelled SHCS emissions per household fell by 1.4%, reflecting the improved energy efficiency of the sector in this period and the greater potential to reduce CO2 emissions. The SHCS estimates are not designed to capture the increased demand for heating due to colder weather or reduced demand associated with warmer weather in any particular year.
Table 23: Carbon Emissions and Modelled Emissions in Scottish Housing, 2011-2017
|Carbon Emissions1: BEIS Domestic sector||Total (Mtonnes)||12.0||12.8||12.3||10.4||10.0||9.3|
|per HH (tonnes)2||5.1||5.3||5.1||4.3||4.1||3.8|
|% change per HH||-12.8%||5.8%||-4.0%||-16.4%||-4.2%||-7.2%|
|Modelled emissions: SHCS||Total (“Mt”)||18.2||18.1||17.4||17.9||17.7||17.2||17.3|
|per HH (“t”)||7.7||7.6||7.3||7.4||7.3||7.0||7.0|
|% change per HH||-2.6%||-1.4%||-3.6%||1.1%||-1.8%||-3.0%||-0.2%|
 Local and Regional CO2 Emissions Estimates, BEIS. Data reflects revisions made in the most recent publication. https://www.gov.uk/government/statistics/uk-local-authority-and-regional-carbon-dioxide-emissions-national-statistics-2005-2016
 Number of households (HHs) sourced from National Records of Scotland, Estimates of Households and Dwellings, 2017: https://www.nrscotland.gov.uk/statistics-and-data/statistics/statistics-by-theme/households/household-estimates/2017
* Modelled emissions figures for 2014 to 2017 are not fully comparable to previous years
118. Estimates in the Second Report on Proposals and Policies (RPP2) or in the Draft Climate Change Plan are also not comparable to SHCS estimates. RPP2 figures for the residential sector relate to non-traded emissions only (i.e. exclude electricity which is covered by the EU Emissions Trading System) while SHCS estimates cover all fuel types.
119. This report is only concerned with the level and variations in modelled emissions from the Scottish housing stock. These estimates are produced through the use of BREDEM 2012-based models, in line with other statistics on energy efficiency and fuel poverty reported here.
120. To derive emissions estimates, modelled energy demand is combined with carbon intensity factors as adopted for the 2012 edition of the SAP (see section 7.3). These are CO2 equivalent figures which include the global warming impact of CH4 and N2O as well as CO2.
121. The change in the underlying BREDEM 2012 model, first implemented in the reporting of 2014 data, has meant that carbon emissions for 2014-2017 are not estimated on a consistent basis with those for 2010-2013. Further details on this change are given in the Methodology Notes to the 2014 Key Findings report.
3.5.1 Modelled Emissions by Dwelling Type and Age of Construction
122. The annual modelled emissions from a property reflect the energy use for the whole dwelling heated according to the standard heating regime. Figure 14 shows that dwellings with larger floor area generally have higher carbon emissions.
123. Newer dwellings have lower modelled emissions than older ones on average as a result of their better thermal performance and higher energy efficiency (as shown in section 3.3). Post-1982 flats have the lowest modelled emissions on average; less than 4 tonnes per year (Table 24) which is around half the average across all dwellings.
Figure 14: Average Floor Area and Average Modelled Annual Emissions by Age and Type of Dwelling, 2017
Note: Floor areas for these subgroups are provided in section 2.1.1. Modelled carbon emissions figures are provided in Table 24.
The pale blue line indicates the average modelled emissions from the dwelling age group.
Table 24: Average Modelled Annual Carbon Emissions (tonnes per year) by Dwelling Age and Type, 2017
|Dwelling Type||Dwelling Age|
|All dwelling types||9.8||6.6||6.0||7.0|
124. Across all age bands, detached houses have the highest modelled emissions due to a larger share of exposed surfaces. As shown in section 2.3, they are also the most likely to use high carbon-intensity fuels such as oil and coal in place of mains gas.
125. By dividing modelled emissions by total internal floor area we derive emissions per square meter (kg/m2). Controlling for floor area in this way shows that pre-1919 detached houses have the highest modelled emissions per sq. m (108 kg/m² ), as shown in Table 25. Post-1982 detached dwellings (58 kg/m2), tenements (56 kg/m2) and other flats (59 kg/m2) have the lowest emissions.
Table 25: Average Modelled Emissions per Square Meter of Floor Area (kg/m2) by Age and Type of Dwelling, 2017
|Dwelling Age||Pre-1919||1919-1982||Post-1982||All Ages|
3.5.2 Modelled Emissions by Tenure
126. Although data for 2014-2017 is not directly comparable to prior years, the data suggests that there is a longer term trend of declining emissions. Average modelled carbon emissions reduced from 92 kg/m2 in 2010 to 80 kg/m2 in 2013. Based on the updated carbon emissions methodology, there was then a further decrease from 80 kg/m2 in 2014 to 74 kg/m2 in 2017.
127. Figure 15 and Table 26 show how emissions differ across tenure for the period 2010-2017. The highest rates of emissions observed for private rented dwellings (83 kg/m2) and lowest for housing association dwellings (68 kg/m2), with emissions from the other tenures falling in between those values. The values were similar to the previous year across all tenures, however the longer time series shows a decreasing trend over the 2010-2017 period for all tenures.
128. Changes to the tenure definitions and the revised carbon emissions methodology mean that figures for 2014-2017 by tenure are not fully comparable to earlier years. Differences that were statistically significant were seen in the mortgaged sector (reducing from 78 kg/m2 in 2014 to 70 kg/m2 in 2017) and households that are owned outright (reducing from 81 kg/m2 to 75 kg/m2 between 2014 and 2017).
Table 26: Average Modelled Emissions per Square Meter by Tenure, 2010-2017*
* Data for 2010 to 2013 does not include households living rent free. Figures for 2014-2017 are therefore not fully comparable to the previous years.
Figure 15: Modelled Emission per square meter (kg/m2) by Tenure, 2010-2017*
* Data for 2010 to 2013 does not include households living rent free. Figures for 2014-2017 are therefore not fully comparable to previous years.
3.6 Environmental Impact Rating
129. The Environmental Impact Rating (EIR) represents the environmental impact of a dwelling in terms of carbon emissions associated with fuels used for heating, hot water, lighting and ventilation. Ratings are adjusted for floor area so they are independent of dwelling size for a given built form. Emissions for this measure are calculated using SAP methodology.
130. EI ratings for 2015, 2016 and 2017, produced on the basis of SAP 2012, are not fully comparable to those for the period 2010-2013, which were produced on the basis of SAP 2009.
131. Figure 16 illustrates the increasing trend in the median EIR between 2010 and 2017. This indicates that the environmental impact of Scottish housing is gradually falling over time.
Figure 16: Median EIR relative to Band, 2010-2013 (SAP 2009) and 2015-2017 (SAP 2012)
132. As shown in Table 27, 32% of dwellings had EI ratings in band C or better, an improvement on the 2016 figure of 29%. The mean rating was 60 and the median was 63, both of which fall in band D.
133. In 2017, 9% of dwellings were rated F or G in terms of their environmental impact.
Table 27: EIR Bands in the Scottish Housing Stock, 2011-2013 and 2015-2017
|A - B (81+)||120||5%||96||4%||102||4%||71||3%||52||2%||55||2%|
134. Figure 17 illustrates that the energy efficiency and the environmental impact rating for the median Scottish dwelling have changed in parallel since 2010.
Figure 17: Trend in Median EE and EI Ratings, 2010-2013 and 2015-2017
135. Table 28 shows how EI ratings vary across different type of dwellings. As expected dwellings built since 1982 have better environmental impact ratings than other dwellings, with 60% rated C or better and only 2% in the bottom two bands (F and G). Flats have a lower environmental impact than houses, as do gas heated properties compared to those using oil or electricity.
136. Oil heating systems and houses are more common in rural areas, leading to lower overall environmental impact ratings for rural dwellings.
Table 28: Mean EIR and Broad EIR Band, by Dwelling Characteristics, 2017
|Environmental Impact Rating Mean||EI Band||Sample|
|Age of Dwelling|
|Primary Heating Fuel|
|Other fuel type||57.8||52%||21%||27%||92|