3 Energy Efficiency
51. 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.
52. 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.
53. 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);
- National Home Energy ratings (NHERs) (section 3.4);
- modelled CO2 emissions from dwellings (section 3.5); and
- Environmental Impact Ratings (section 3.6).
3.1 Insulation Measures
54. 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, see Chapter 4 on Fuel Poverty.
55. 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 2019, loft insulation with a thickness of 100 mm or more had been installed in 94% of dwellings. This has been stable since 2015 but represents an increase of 12 percentage points on 2010 levels.
- In 2019, 30% of lofts were insulated to a high standard of insulation (300 mm or more). This proportion has remained about this level since 2015, following year on year increases from the 2010 figure of 5%.
- The proportion of insulated cavity walls recorded by the SHCS was 73% in 2019, similar to the previous year. In the longer term, the share of insulated cavity walls has been increasing, with a 7 percentage point improvement since 2012.
- The proportion of solid wall dwellings with insulation was 18% in 2019, which was similar to 2018, 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. 55% of homes in the private sector have wall insulation compared to 70% in the social sector. In the private sector, 63% of lofts are insulated to 200 mm or more compared to 71% in the social sector.
3.1.1 Loft Insulation
56. Since 2010, there has been an overall improvement in the uptake of loft insulation. 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 2019 (see Table 10) Table 10, similar to the level in 2018. Most of this improvement occurred before 2013.
57. 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 2019. 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 uninsulated lofts.
58. Over the same period the thickness of loft insulation has increased significantly. In 2019, 65% of dwellings with lofts had insulation with a depth of 200 mm or more (Figure 9). 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. There has been a decrease in the share of dwellings with loft insulation with a depth of 100-199 mm between 2018 and 2019. However there is no significant associated increase in the share of dwellings with 200+ mm.
59. The percentage of lofts with a high standard of insulation (300 mm or more) has remained similar since 2015, at 30%, following significant increases from 5% in 2010 (the first year the SHCS captured this information). In 2019, 29% of private sector dwellings had a high standard of loft insulation, lower than 37% of dwellings in the social sector. The difference between the sectors and the levels of each were similar in 2018.
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).
60. Between April 2008 and December 2012, the UK government Carbon Emissions Reduction Target (CERT) scheme delivered 410,937 loft insulation measures in Scotland (Table 10).
61. Between January 2013 and December 2019 a further 73,482 loft insulation measures were delivered in Scotland by its successor scheme, the Energy Company Obligation (ECO).
62. In total, around 484,000 loft insulation measures have been installed under these government programs since 2008.
|200mm or more||1,217||1,135||1,152||1,197||1,161||975||621|
|Cumulative recorded loft insulations under government schemes|
Note: There were fewer insulation measures installed under ECO in 2019 compared to earlier years as ECO3, which went live in December 2018, focuses exclusively on Affordable Warmth resulting in a greater number of heating measures (including boiler measures). In total, there were around 5% more ECO measures installed in 2019 compared to 2018 across Great Britain however 12% of these were loft insulation measures compared to 19% in 2018.
63. As shown in Table 11 thickness of loft insulation is greater in social sector dwellings than private sector dwellings. In 2019, 93% of private housing lofts were insulated to 100 mm or more and 63% to at least 200 mm. In the social sector, 96% of dwellings had lofts insulated to 100 mm or more, and 71% had at least 200 mm of loft insulation.
64. One of the reasons for the 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).
65. 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 3 percentage points in 2019 (96% in the social sector and 93% in the private sector).
|Year||Loft Insulation||Private Sector||Social Sector||All Tenures|
|1mm - 99mm||91||6%||14||3%||105||6%|
|100mm - 199mm||446||30%||101||25%||547||29%|
|200mm - 299mm||509||34%||135||33%||643||34%|
|300mm or more||423||29%||151||37%||574||30%|
|1mm - 99mm||82||6%||13||3%||95||5%|
|100mm - 199mm||494||34%||101||26%||594||32%|
|200mm - 299mm||444||31%||149||38%||594||32%|
|300mm or more||412||29%||130||33%||542||30%|
Note: Dwellings without loft spaces are excluded.
3.1.2 Wall Insulation
66. 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 concealing their work. This may mean that the SHCS under-estimates the number of homes which have had CWI installed (see also section 126.96.36.199). Despite efforts to maintain the high quality of the SHCS physical survey fieldwork, some misclassifications may remain.
67. 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. As the improvement of solid and other wall types generally requires more expensive interventions than CWI, this diverse group is addressed together in this chapter.
68. Table 12 and Table 13 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 1983 when the Building Standards (Scotland) Amendment Regulations 1982 came into force. These dwellings are therefore treated as insulated when built.
|Cumulative reduction in SHCS uninsulated since 2007|
|Cumulative recorded CWI installations under government schemes since 2007, thousands|
1. Dwellings built post-1983 are presumed insulated when built.
2. There were fewer insulation measures installed under ECO in 2019 compared to earlier years as ECO3, which went live in December 2018, focuses exclusively on Affordable Warmth resulting in a greater number of heating measures (including boiler measures). In total, there were around 5% more ECO measures installed in 2019 compared to 2018 across Great Britain however 19% of these were cavity wall insulation measures compared to 38% in 2018.
69. In 2019, 73% of cavity wall dwellings in Scotland were insulated (Table 12), similar to 2018. Administrative data shows that 3,824 cavity wall dwellings were insulated with CWI during 2019 (through ECO).
70. The longer term trend, showing a decrease in the share of uninsulated cavity walls of 7 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.
71. 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 2019 a further 104,137 cavity and 65,122 solid wall insulation measures were delivered in Scotland by the successor ECO scheme. This equates to around 396,000 wall insulation measures, including around 322,000 cavity wall insulation measures, installed under these programs by the end of 2019. This is reflected in the estimated cumulative reduction of 306,000 uninsulated cavity wall dwellings reported by the SHCS since 2007.
72. Table 13 shows the levels of insulation in dwellings with solid or other construction type walls recorded by the survey in 2019. The results show that 18% of dwellings in this category had insulated walls in 2019; the difference with the level recorded in the previous year (19%) is not statistically significant but is an increase of 7 percentage points from 2012. Only 719 dwellings with solid walls were surveyed in 2019 as part of the SHCS. This relatively small sample does not allow enough precision to capture the increase in solid wall insulation measures which administrative data shows is taking place. Since the beginning of January 2013 at least 65,122 solid wall insulation measures were delivered in Scotland under ECO.
|Cumulative recorded installations under government schemes since 2007, thousands|
1. Dwellings built post-1983 are presumed insulated when built. ECO figures will include a small number of cavity walls with solid wall insulation types.
2. There were fewer insulation measures installed under ECO in 2019 compared to earlier years as ECO3, which went live in December 2018, focuses exclusively on Affordable Warmth resulting in a greater number of heating measures (including boiler measures). In total, there were around 5% more ECO measures installed in 2019 compared to 2018 across Great Britain however 6% of these were cavity wall insulation measures compared to 9% in 2018.
73. The information in Table 14 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 7.8.6). HTTCs have certain attributes which make CWI more expensive, complex or inadvisable. Standard cavity walls have no such barriers.
74. In the social sector, three quarters (74%) of cavity wall dwellings and 42% of dwellings with solid and other wall types were estimated to have insulation in 2019. Nearly three-quarters (70%) of social housing overall had insulated walls.
75. In the private sector, nearly three quarters (72%) of cavity wall dwellings and 14% of solid and other wall dwellings, had insulation in 2019. Over half (55%) of all private sector dwellings had insulated walls.
76. 36% 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 such as with internal and external wall insulation.
77. Levels of insulation are higher in the social sector at 70% (all wall types) compared with 55% 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 (14% of cavity wall dwellings in the social sector; 3% of private dwellings) and retrofit solid wall insulation measures (42% of solid wall dwellings in the social sector; 11% in the private sector).
|Wall and Insulation Type||Private Sector||Social Sector||Total|
|- As built||434||33%||23%||133||24%||21%||567||30%||23%|
|- As built||13||2%||1%||0||1%||0%||13||2%||1%|
|All Wall Types|
|All Wall Types: 2018|
Note: Dwellings built post-1983 are presumed insulated when built.
- In 2019, 64% of gas and oil boilers met the minimum efficiencies specified by the current Building Standards, similar to 2018. This has increased substantially from 30% in 2012.
78. The heating system is a key factor in the thermal efficiency of a dwelling. Around 87% 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, details are available in the Domestic Building Services Compliance Guide for Scotland.
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 2012-2019 data collections. For these years we can track the improved efficiency 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. All subsequent data is published on the basis of the new methodology and further details can be found in section 7.6.
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% for gas and LPG; for ranges, back boiler and combined primary storage units (CPSUs), 75% when gas, and 80% when oil.
|Households using gas or oil boilers for heating|
|… of which|
|% "New" boilers (post-1998)||94%||92%||91%||91%||89%||85%||83%||81%|
|% condensing boilers||76%||73%||67%||61%||56%||48%||43%||38%|
|% standards compliant boilers||64%||62%||57%||52%||47%||41%||33%||30%|
|Sample size (gas/oil boilers)||2,518||2,489||2,475||2,356||2,259||2,195||2,219||2,488|
83. In 2019 the survey found that 94% of the domestic gas and oil boilers in Scotland have been installed since 1998, when the European Boiler Efficiency Directive minimum standards came into effect. The proportion of new boilers, those installed since 1998, has increased by 24 percentage points since 2010.
84. In 2019, over three-quarters (76%) of gas and oil boilers were condensing boilers. This represents a rapid increase of 4 percentage points since 2018 and 54 percentage points since 2010.
85. In 2019, 64% of gas and oil boilers met the minimum efficiencies specified by the current Building Standards, similar to 2018 (62%). This has increased substantially from 30% in 2012.
3.3 Energy Performance Certificates
- In 2019, 45% of Scottish homes were rated as EPC band C or better under SAP 2012 (RdSAP v9.93), this is similar to 2018.
- Under SAP 2012 (RdSAP v9.92), 47% of Scottish homes were rated as EPC band C or better in 2019. This represents a 3 percentage point increase compared to 2018 and an 11 percentage point increase from 2014 (the first year in which data based on SAP 2012 is available).
- Under SAP 2009, which allows comparisons over a longer period, over half of dwellings (51%) were rated C or better, up 27 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 12% in 2019.
- Under SAP 2009, the median EE rating was 69, the first time this has been in band C. This is an increase from 62 in 2010 which is equivalent to band D.
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 higher fuel bills, while 100 represents very high energy efficiency and lower 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 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 five years of data are available.
92. SAP is periodically reviewed by the UK government to ensure it remains fit for purpose and to address its continued 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.
93. SHCS energy modelling for SAP 2012 in this report is based on two versions of RdSAP. The first, RdSAP v9.92 which was released on 7 December 2014, 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 the Department for Business, Energy and Industrial Strategy (BEIS).
94. The latest version of RdSAP (v9.93) was released on 19 November 2017 and contains revisions to the underlying assumptions used within the SAP calculations. The most notable update to the methodology in v9.93 was a change to the default U-values of cavity, solid and stone walls, built prior to 1976. Compared to v9.92, U-values for solid, insulated stone and uninsulated cavity walls have improved, whereas they have declined for insulated cavity walls.These U-values are used to calculate the rate of heat loss through the walls, which contributes to the overall thermal performance of the building fabric of the dwelling. Data on the basis of RdSAP v9.93 is presented for 2018 and 2019 only.
3.3.1 Energy Efficiency Rating, SAP 2009
95. Table 16 shows the trend in mean EERs based on SAP 2009, which rose from 59.9 in 2010 to 66.4 in 2019. 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 2018 and 2019 was less than 1% which is not statistically significant.
96. The median EE Rating has also improved since 2010. In 2019, half of all Scottish dwellings were rated 69 or better, the first time that the median EE rating has fallen in EPC band C, and an increase from 62 in 2010 (Figure 10).
97. The Scottish housing stock is gradually becoming more energy efficient as shown by the increases in number of dwellings in bands B and C and corresponding decreases in the lower bands (Figure 11 and Table 17).
98. Over half (51%) of the housing stock in 2019 had an EPC rating of C or better, up 27 percentage points since 2010 (Table 17). Over the same period, the proportion of properties in the lowest EPC bands, E, F and G, has dropped 15 percentage points: 27% of properties were rated E, F or G in 2010 compared with 12% in 2019.
Note: Values for this figure are provided in Table 17.
Note: No A-rated properties were sampled between 2010 and 2019.
3.3.2 Energy Efficiency Rating, SAP 2012
99. This section examines the energy efficiency profile of the Scottish housing stock in 2018 under the most recent SAP 2012 methodology. Time series analysis includes 2018 and 2019 data for both SAP 2012 RdSAP v9.93 and SAP 2012 RdSAP v9.92. Further breakdowns by characteristics of 2019 data are presented under the updated methodology alone: SAP 2012 (RdSAP v9.93).
100. 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 EERs tend to be slightly lower under SAP 2012 compared to SAP 2009.
101. Table 18 and Table 19 show the energy efficiency profile of the Scottish housing stock between 2014 and 2019 under SAP 2012. Figure 12 shows this alongside the longer term change as measured by SAP 2009.
|EER (RdSAP v9.92)||Mean||65.1||64.8||64.3||63.7||62.8||62.2|
|EER (RdSAP v9.93)||Mean||64.9||64.7|
102. In 2019, the mean energy efficiency rating of the Scottish housing stock under SAP 2012 (RdSAP v9.93) was 64.9 and the median was 67 points, indicating that half of the housing stock has an energy efficiency rating of 67 or better (Table 18). The difference in mean rating between 2018 and 2019 was not significant.
103. In 2019, the mean energy efficiency rating of the Scottish housing stock under SAP 2012 (RdSAP v9.92) was 65.1 and the median was 68 points. The difference in mean rating between 2018 and 2019 was not significant. However, there has been an overall improvement since 2014 when the mean was 62.2.
104. Over two-fifths (45%) of all properties in 2019 were rated C or better under SAP 2012 (RdSAP v9.93) (Table 19). Less than a fifth (14%) were in bands E, F or G. Both of these are similar to 2018.
105. Almost half (47%) of all properties in 2019 were rated C or better under SAP 2012 (RdSAP v9.92), this is an increase of 3 percentage points from 2018 and 11 percentage points from 2014. Less than a fifth (15%) were in bands E, F or G - a drop of 6 percentage points over the 5-year period from 2014 to 2018.
106. The update to the underlying methodology had little effect in 2019. Both the mean and median EERs were similar for SAP 2012 (RdSAP v9.92) and SAP 2012 (RdSAP v9.93). Similarly, the distribution of the Scottish housing stock across EPC bands were similar for SAP 2012 (RdSAP v9.92) and SAP 2012 (RdSAP v9.93).
|SAP v 9.92||A (92-100)||-||-||-||-||-||-||-||-||-||-||-||-|
|SAP v 9.93||A (92-100)||-||-||-||-|
Note: No A-rated properties were sampled for 2014-2019
107. Figure 12 shows EPC bandings for SAP 2009 and SAP 2012 (RdSAP v9.92 and RdSAP v9.93). 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 51% in 2019 (as measured under SAP 2009), and 35% in 2014 to 47% in 2019 (as measured under SAP 2012 (RdSAP v9.92)).
108. Table 20 shows the energy efficiency profile by broad tenure groups in 2019 using SAP 2012 (RdSAP v9.93). Figure 13 provides more details on the distribution of the least energy efficient properties by household characteristics.
|EPC Band||Owner occupied||Private rented||Social sector||All Tenures|
|F & G (1-38)||73||5%||32||10%||6||1%||111||4%|
109. Over half (56%) of social housing is in band C or better under SAP 2012, compared to two-fifths (40%) in the private rented sector and owner-occupied sector (41%). 6 per cent of dwellings in the social sector are within EPC bands E, F or G, while 17% of owner occupied dwellings and 20% 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.
110. Figure 13 shows that the share of dwellings in the lowest energy efficiency bands (F and G) is particularly high for pre-1919 dwellings (13%), non-gas heated properties (between 18% and 24%), detached properties (10%) and in the private rented stock (10%). Across Scotland as a whole, 4% of properties were in bands F or G in 2019.
Note: Base figures and more detailed breakdowns are provided in Table 21 and Table 22.
111. More detailed 2019 breakdowns are shown in Table 21 by household characteristics.
112. Mean SAP 2012 (RdSAP v9.93) ratings ranged from 62.0 in private rented dwellings to 71.0 in housing association dwellings, a statistically significant difference. Social housing as a whole is more energy efficient than the private sector, with a mean EER of 68.5 compared to 63.7 for private dwellings.
113. Older households (63.2) have lower average EER ratings than families (67.7) and other (adults without children) households (64.7).
114. Mean EER ratings ranged from 63.2 to 66.3 across income bands with the highest rating for £400 - £499.99 weekly household income. Average EER ratings ranged from 62.2 to 66.0 across council tax bands with the highest rating found in Band C.
|SAP 2012 Ratings||EPC Band||Sample|
|Weekly Household Income|
|Council Tax Band|
|Band G & H||62.2||39%||54%||7%||201|
115. Table 22 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 61.2) while flats have the highest rating (68.4 for tenements and 67.2 for other flats). The energy efficiency ratings did not change for most dwelling types between 2018 and 2019 with the exception of dwellings built after 1982 where the proportion of dwellings with EPC band above C increased by 1 percentage point.
116. The oldest, pre-1919, properties are least energy efficient (mean EER of 55.5 and only 19% rated C or better) while those built after 1982 have the highest energy efficiency ratings (mean EER of 72.6, with 77% in band C or better); the mean EER for dwellings built after 1982 has increased 1 percentage point since 2018.
117. Primary heating fuel is a key determinant of the energy efficiency of the dwelling. Properties heated by mains gas have an average rating of 67.5 and 50% 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 49.2 (making the average dwelling in this group E rated) and only 8% are in band C or better.
118. Proximity to the gas grid has a similar effect on the energy efficiency rating (average SAP rating 66.3 for dwellings near the gas grid, higher than the 58.1 for other dwellings).
119. 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 22 shows that mean SAP 2012 rating is 66.7 for dwellings in urban areas, higher than the 56.2 for dwellings in rural areas.
|SAP 2012 Ratings||EPC Band||Sample|
|Age of dwelling|
|Other fuel type||56.1||35%||41%||24%||95|
3.4 National Home Energy Ratings (NHER)
120. 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.
121. Table 23 presents banded NHER scores and mean values for selected categories of dwellings and household types for 2019. Significant differences were seen by age of dwelling, with older dwellings having lower average values (6.2 for pre-1919) than properties that were built more recently (8.8 for post-1982). Private sector dwellings had significantly lower NHER scores (7.4) than social sector (8.2) with mean scores by detailed tenure ranging from 7.2 (owned outright) to 8.7 (housing associations). There were also differences by dwelling type ranging from detached properties at 7.1 to tenements at 8.2. Dwellings using oil as their main fuel had the lowest score at 5.7 while those fuelled by gas had the highest at 8.0.
122. Table 23 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 (67% of detached properties, compared to 84% of other flats) and age of dwelling (48% of pre-1919 dwellings compared to 94% of post-1982 dwellings). Primary heating fuel also had an impact on the proportion that were rated as good (85% of dwellings with gas as a primary fuel, compared to just 36% of dwellings with oil as a primary fuel). This profile is similar to SAP 2012 (RdSAP v9.93).
|NHER (emulated)||NHER band||Sample|
|Age of dwelling|
|Primary Heating Fuel|
|Other fuel type||7.0||59%||33%||8%||95|
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 2019, which is approximately double the average carbon emissions per household as reported by BEIS (3.5 tonnes per year) in 2018, based on actual energy use. This suggests that households are not heating their homes to the standard heating regimes.
- Average modelled carbon emissions for all properties was 73 kg/m2 in 2019 which has been stable since 2017 following a decrease from 80 kg/m2 in 2014.
123. Carbon Emissions are the amount of greenhouse gas emissions, expressed as their carbon dioxide gas equivalent, vented to the atmosphere. Estimates of emissions from the residential sector which take into account actual energy consumption by households are reported annually by BEIS in the Local and Regional CO2 Emissions Estimates. 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.
124. 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.
125. Table 24 shows modelled emissions from the SHCS and provides a comparison with the estimates published by BEIS for the period 2013-2018.
126. Average carbon emissions per household have decreased year on year since 2013, accompanied by a decrease in the SHCS based average modelled emissions, with the exception of 2014 and 2019. This is accompanied by an increase in number of dwellings from 2.4 million in 2013 to 2.5 million in 2019 as reported by National Records of Scotland.
127. There was a methodology change from 2014 so the modelled emissions figures between 2013 and 2014 are not fully comparable, details of this are provided in the 2014 Methodology Notes. 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.
|Carbon Emissions: BEIS Domestic sector||Total ("Mt")||8.7||8.8||9.4||10.0||10.4||12.3|
|per HH (t"")||3.5||3.6||3.8||4.1||4.3||5.1|
|% change per HH||-1.6%||-6.8%||-6.7%||-4.7%||-15.8%||-4.0%|
|Modelled emissions: SHCS||Total ("Mt")||17.4||16.8||17.3||17.2||17.7||17.9||17.4|
|per HH ("t")||7.0||6.8||7.0||7.0||7.3||7.4||7.3|
|% change per HH||2.5%||-3.2%||-0.2%||-3.0%||-1.8%||1.1%||-3.6%|
1 Local and Regional CO2 Emissions Estimates, BEIS. Data reflects revisions made in the most recent publication.
2 Number of households (HHs) sourced from National Records of Scotland, Estimates of Households and Dwellings, 2019.
3 Modelled emissions figures for 2014-2019 are not fully comparable to the previous years.
128. Estimates in the Third Report on Proposals and Policies (RPP3) or in the Climate Change Plan are also not comparable to SHCS estimates. RPP3 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.
129. 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. Information on the energy modelling is available in the Methodology Notes.
130. 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.
131. The change in the underlying BREDEM 2012 model, first implemented in the reporting of 2014 data, has meant that carbon emissions for 2014-2019 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
132. 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.
133. 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 25).
Note: Floor areas for these subgroups are provided in section 2.1.1. Modelled carbon emissions figures are provided in Table 25. The blue line indicates the average modelled emissions for the dwelling age group.
|Dwelling Type||Dwelling Age|
|All dwelling types||10.1||6.4||5.7||7.0|
134. 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.
135. By dividing modelled emissions by total internal floor area we derive CO2 emissions per square meter (kg/m2). Controlling for floor area in this way shows that pre-1919 detached (106 kg/m²) and pre-1919 semi-detached (105 kg/m2) houses have the highest modelled emissions per sq. as shown in Table 26. Post-1982 dwellings have the lowest emissions, particularly detached dwellings (57 kg/m2), tenements (56 kg/m2) and other flats (54 kg/m2).
|Dwelling Type||Dwelling Age|
|All dwelling types||93||74||58||73|
3.5.2 Modelled Emissions by Tenure
136. Although data for 2014-2019 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 and then remaining stable at 73 kg/m2 in 2018 and 2019.
137. Table 27 and Figure 15 show how emissions differ across tenure for the period 2010-2019. The highest emissions were observed for private rented dwellings (85 kg/m2) and lowest for housing association dwellings (66 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 2010-2019 period for all tenures.
138. Changes to the tenure definitions and the revised carbon emissions methodology mean that figures for 2014-2019 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 2019) and households that are owned outright (reducing from 81 kg/m2 to 75 kg/m2 between 2014 and 2019).
Note: Data prior to 2014 does not include households living rent free. Figures for 2014-2019 are therefore not fully comparable to the previous years.
Figure 15: Modelled Emissions per square meter (kg/m2) by Tenure, 2010-2019
Note: Data prior to 2014 does not include households living rent free. Figures for 2014-2019 are therefore not fully comparable to previous years.
3.6 Environmental Impact Rating
139. 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.
140. Paragraphs 91 to 94 in Section 3.3 describe the versions of SAP and RdSAP available in this publication. 2019 EIRs have been described in this report based on SAP 2012 under both RdSAP v9.92 and v9.93. EI ratings for 2015-2019, 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.
141. Figure 16 illustrates the increasing trend in the median EIR between 2010 and 2019. This indicates that the environmental impact of Scottish housing is gradually falling over time but has always remained within band D.
142. The update to RdSAP v9.93 in SAP 2012 had no effect on the median EIR in 2019 which was the same for both SAP 2012 versions (Table 28).
143. As shown in Table 28, one third of dwellings had EI ratings in band C or better under SAP 2012 (RdSAP v9.93) in 2019, this is similar to 2018. The mean rating was 61 and the median was 64, both of which fall in band D.
144. Under SAP 2012 (RdSAP v9.92) 36% of dwellings had EI ratings in band C or better, which is similar to 2018. The mean rating was 61 and the median was 64, both of which fall in band D.
145. In 2019, 9% of dwellings were rated F or G in terms of their environmental impact under both SAP 2012 versions.
|SAP v9.92||A - B (81+)||150||6%||136||6%||120||5%||96||4%||102||4%||71||3%|
|SAP v9.93||A - B (81+)||140||6%||125||5%|
Note: Data prior to 2014 does not include households living rent free. Figures for 2014-2018 are therefore not fully comparable to previous years.
146. Figure 17 illustrates that the energy efficiency and the environmental impact rating for the median Scottish dwelling have changed in parallel since 2010.
147. Table 29 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 65% rated C or better and only 2% in the bottom two bands (F and G). Flats have a lower environmental impact (higher EI rating) than houses, as do gas heated properties compared to those oil or electricity.
148. Oil heating systems and houses are more common in rural areas, leading to lower overall environmental impact ratings for rural dwellings.
|Environmental Impact Rating||EI Band (SAP 2012 v9.93)||Sample|
|Age of dwelling|
|Primary Heating Fuel|
|Other fuel type||57.7||*||18%||*||95|
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