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);
- Energy Efficiency Ratings ( EER), also known as SAP ratings ( section 3.3);
- modelled CO 2 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 increase thermal comfort and reduce heating bills.
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. As of 2016, at least 100 mm of loft insulation is installed in an estimated 94% of lofts. This is an increase of 12 percentage points on 2010 levels.
- In 2016, 30% of lofts were insulated to a high standard of insulation (300 mm or more). This is similar to 2015 and follows significant increases from 5% in 2010.
- The proportion of insulated cavity walls recorded by the SHCS was 72% in 2016. This is similar to the previous year. In the longer term the share of insulated cavity walls has been increasing, with a 6 percentage points improvement since 2012.
- The proportion of solid wall dwellings with insulation was 15% in 2016 compared to 11% in 2015 although this difference is not significant.
- Levels of insulation (both loft and wall) are higher in the social sector than in the private sector. 53% of walls (all types) are insulated in the private sector compared to 71% in the social sector. 62% of lofts are insulated to 200 mm or more in the private sector compared to 78% in the social sector.
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 2016 (see Table 10), similar to the level in 2015. Most of this improvement occurred before 2013.
56. Figure 9 shows the level of loft insulation in all dwellings back to 2003/4. The number of dwellings with no loft insulation has fallen from 6% in 2003/4 to 1% in 2016. 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 2016, 65% of dwellings with lofts had insulation with a depth of 200 mm or more. Much of this increase has occurred since 2009, when 27% of lofts fell into this group and can largely be attributed to the installation of top up insulation. In 2016, 643,000 lofts had less than 200 mm of insulation.
58. The percentage of lofts with a high standard of insulation (300 mm or more) has remained similar to 2015, following significant increases. While only 5% of lofts were insulated to this standard in 2010 (the first year the SHCS captured this information), by 2016 this figure had increased to 30%. Whilst the rate for 2015 was 32%, the difference compared to 2016 is not statistically significant. Although there appears to have been a drop in the percentage of social sector lofts insulated to this standard, this difference is also not significant.
Figure 9: Depth of Loft Insulation (where applicable) 2003/04 - 2016
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 2016 a further 52,853 loft insulation measures were delivered in Scotland by its successor scheme ECO  .
61. In total, around 464,000 loft insulation measures have been installed under these government programs since 2008 .
Table 9: Depth of Loft Insulation (000s), 2010 to 2016
|200mm or more||1,197||1,161||1,123||1,118||975||812||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. In 2016, 93% of private housing lofts were insulated to 100 mm or more and 62% to at least 200 mm. In the social sector, 97% of dwellings had lofts insulated to 100 mm or more, and 78% had at least 200 mm of loft insulation.
Table 10: Depth of Loft Insulation (000s and %) by Tenure, 2015 and 2016 
|Year||Loft Insulation||Private Sector||Social Sector||All Tenures|
|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%|
|1mm - 99mm||113||8%||13||4%||125||7%|
|100mm - 199mm||442||30%||76||21%||518||28%|
|200mm - 299mm||455||31%||121||33%||576||32%|
|300mm or more||435||30%||150||41%||585||32%|
63. One of the reasons for this difference between private and social sector is that the Scottish Housing Quality Standard ( SHQS) requires at least 100 mm of loft insulation. The SHQS was introduced in 2004, and all social rented dwellings were required to meet this standard by 2015 (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 2016 (97% in the social sector and 93% in the private sector).
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 to 2016 
|Cumulative reduction in SHCS uninsulated since 2007|
|Cumulative recorded cavity wall insulations under government schemes since 2007|
68. In 2016 72% of cavity wall dwellings in Scotland were insulated ( Table 11), similar to 2015. We know from administrative data that 9,532 cavity wall dwellings were insulated during 2016 (through ECO). However, although the number 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, which shows a decrease in the share of uninsulated cavity walls of 6 percentage points since 2012, is broadly consistent with administrative data on the number of cavity wall insulation measures installed under the UK Government Carbon Emissions Reduction Target ( CERT) and the Energy Company Obligation ( ECO). Between April 2008 and December 2012, the CERT scheme delivered around 227,000 wall insulation measures in Scotland  (218,000 cavity and 9,000 solid and other walls). Between January 2013 and December 2016 a further 81,743 cavity and 40,814 solid wall insulation measures were delivered in Scotland by the successor ECO scheme  . This equates to a total of around 350,000 wall insulation measures being installed under these two government programs by the end of 2016, including around 300,000 cavity wall insulation measures. This is almost identical to the cumulative reduction of 304,000 uninsulated cavity wall dwellings reported by the SHCS since 2007 ( Table 11).
70. Table 12 shows the levels of insulation in dwellings with solid or other construction type walls recorded by the survey in 2016. The results show that 15% of dwellings in this category had insulated walls. The difference with the level recorded in the previous year (11%) is not statistically significant. Only 696 dwellings with solid walls were surveyed in 2016 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 40,814 solid wall insulation measures were delivered in Scotland  ; however the proportion of insulated solid wall dwellings recorded by the SHCS has stayed more or less constant with no significant differences between years.
71. Further information on insulation levels by wall type for the private and social housing stock is provided in Table 13.
Table 12: Wall Insulation of Solid and Other Wall Types, 2012 to 2016 
|Cumulative recorded EWI installations under government schemes since 2007, thousands|
72. Around three quarters (76%) of cavity wall dwellings and around two-fifths (42%) of dwellings with other wall types in the social sector are estimated to have insulation in 2016. Over two-thirds (71%) of social housing overall had insulated walls.
73. Over two thirds (70%) of private sector cavity wall dwellings, and around one tenth (11%) of solid wall dwellings, had insulation in 2016. Just over half (53%) of all private sector dwellings had insulated walls.
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 on the definition are available in section 7.8.6.). HTTCs have certain attributes which make CWI more expensive, complex or simply inadvisable. Standard cavity walls have no such barriers.
75. Overall, the majority of work done to cavity walls has been CWI; 37% of cavity wall dwellings in Scotland have had retrofit cavity wall insulation, which is generally the lowest cost improvement available.
76. Levels of insulation are higher in the social sector at 71% (all wall types) compared with 53% 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 compared to 3% in the private) and retrofit solid wall insulation measures (39% of solid wall dwellings in the social sector compared to 8% in the private).
77. No statistically significant improvement in wall insulation levels is 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 2015 in wall insulation amongst households in the social sector is within the margin of error.
Table 13: Insulation by Wall Type and Tenure, 2016 and Insulation of all Wall Types by Tenure, 2015 and 2016 
|Wall and Insulation Type||Private Sector||Social Sector||Total|
|- As built||421||32%||23%||114||22%||18%||536||29%||22%|
|- As built||12||2%||1%||*||*||*||14||2%||1%|
|All Wall Types|
|2015: All Wall Types|
In 2016, 52% of gas and oil boilers meet the minimum efficiencies specified by current Building Standards, an increase of 5 percentage points from 2015.
78. The heating system is a key factor in the thermal efficiency of a dwelling.
79. Around 86% 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:
- Frolacement boilers 
- m 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 rep
80. 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.
81. 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 2012-2016 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.
82. The methodology by which boiler efficiency ratings are calculated changed in 2016 and the time series has been updated to reflect this. Additionally, the time series now accounts 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 therefore does not match that published in previous reports. Further details on the methodology change can be found in section 7.6.
83. 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 & 2012-2016.
|Households using gas or oil boilers for heating|
|… of which|
|% "New" boilers (post-1998)||91%||89%||85%||83%||81%||70%|
|% condensing boilers||61%||56%||48%||43%||38%||22%||7%|
|% standards compliant boilers||52%||47%||41%||33%||30%|
|Sample size (gas/oil boilers)||2,356||2,259||2,195||2,219||2,222||2,488||2,410|
84. In 2016 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 in accordance with this directive has increased by 21 percentage points since 2010.
85. In 2016, over half (61%) of gas and oil boilers were condensing boilers. This represents a rapid increase of 39 percentage points since 2010.
86. In 2016, 52% of gas and oil boilers meet the minimum efficiencies specified by current Building Standards, an increase of 5 percentage points from 2015. 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 2016, 39% of Scottish homes were rated as EPC band C or better under SAP 2012, up 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, over two fifths of dwellings (43%) were rated C or better , up 19 percentage points since 2010. In the same period, the proportion of properties in the lowest EPC bands (E, F or G) has almost halved, reducing from 27% to 14%.
87. 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.
88. 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 building, taking into account the energy needed for space and water heating, ventilation and lighting and, where relevant, energy generated by renewables.
89. 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.
90. Ratings are adjusted for floor area so that they are essentially independent of dwelling size for a given built form.
91. 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).
92. 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 three years of data are available.
3.3.1 Energy Efficiency Rating, SAP 2009
93. Table 15 shows the trend in mean EERs, which rose from 59.9 in 2010 to 65.1 in 2016. 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, with no significant difference between 2015 and 2016.
Table 15: Average EER for 2010 – 2016, SAP 2009
94. The median EE Rating has also improved over this period. In 2016 half of all Scottish dwellings were rated 67 or better, similar to the previous two years, an increase from 62 in 2010.
Figure 10: Median EER relative to EPC bands, SAP 2009, 2010-2016
95. 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, 2012-2016
Note: Values for this figure are provided in Table 16.
96. Just over two-fifths (43%) of the housing stock in 2016 had an EPC rating of C or better, up 19 points since 2010 (Table 16). Over the period 2010-2016, the proportion of properties in the lowest EPC bands, E, F and G, has dropped 13 percentage points: 27% of properties were rated E, F or G in 2010 compared with 14% in 2016.
Table 16: Distribution of the Scottish Housing Stock by EPC Band, SAP 2009, 2010-2016
No A-rated properties were sampled between 2010 and 2016.
3.3.2 Energy Efficiency Rating, SAP 2012
97. This section examines the energy efficiency profile of the Scottish housing stock in 2016 under the most recent SAP 2012  methodology.
98. 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.
99. On 7 December 2014, a new edition of RdSAP (version 9.92)  was implemented across the UK. In addition to introducing some technical updates and broadening of scope (for example, enabling assessment of 'park homes' as a dwelling type), the new edition includes updated UK carbon factors and fuel costs based upon recent research undertaken by BEIS.
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 SAP fuel prices for these fuels have risen more than for mains gas. As a result, average energy efficiency ratings tend to be slightly lower under SAP 2012 compared to SAP 2009.
101. Tables 17 and 18 show the energy efficiency profile of the Scottish housing stock between 2014 and 2016 under SAP 2012. Figure 12 shows this alongside the longer term change as measured by SAP 2009.
Table 17: Average EER for 2014-2016, SAP 2012
102. In 2016, the mean energy efficiency rating of the Scottish housing stock under SAP 2012 was 63.7 and the median was 66 points, indicating that half of the housing stock has an energy efficiency rating of 66 or better. The improvement in the mean rating between 2015 and 2016 is statistically significant.
103. Over a third (39%) of all properties were rated C or better, an increase from 35% in 2014. Less than a fifth (17%) were in bands E, F or G – a drop of four percentage points in the same period.
Table 18: Distribution of the Scottish Housing Stock by EPC Band, 2014 – 2016, SAP 2012
No A-rated properties were sampled for 2014-2016.
104. Figure 12 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% to 43% of the stock (as measured under SAP 2009), equivalent to a 77% improvement in the share of the most energy efficient dwellings. The observed improvement in the last year, as measured by both SAP 2009 and SAP 2012 is within the margin of error for this survey.
Figure 12: Grouped EPC Bands under SAP 2009 and SAP 2012, 2010-2016
105. Table 19 shows the energy efficiency profile by broad tenure groups in 2016 using SAP 2012. Figure 13 provides more details on the distribution of the least energy efficiency properties by selected characteristics.
Table 19: EPC Band by Broad Tenure in 2016, SAP 2012
|EPC Band||Owner occupied||Private rented||Social sector||All Tenures|
106. Over half (53%) of social housing is in band C or better under SAP 2012, compared to under two-fifths (38%) in the private rented sector. Eight per cent of dwellings in the social sector are in bands E, F or G, while 19% of owner occupied dwellings and 26% of the private rented sector are within these EPC bands.
107. 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 13% and 18%), detached properties (10%) and in the private rented stock (7%) (Figure 13). The average for Scotland as a whole is 4%.
Figure 13: Proportion of Homes in Band F or G by Dwelling Age, Primary Heating Fuel, Tenure and Household and Dwelling Type in 2016, SAP 2012
108. More detailed breakdowns are shown in Table 20 (by household characteristics) and Table 21 (by dwelling attributes). The average EER for Housing Association dwellings is higher than other tenure groups, at 69.9. Social housing as a whole is more energy efficient than private sector dwellings, with a mean EER of 67.6 compared to 62.4 for private dwellings.
Table 20: Mean EER and Broad EPC Band, by Household Characteristics 2016, SAP 2012
|Mean||Differences from 2015 1||BC||DE||FG|
|Weekly Household Income|
|Council Tax Band|
|Band G & H||62.6||40%||52%||8%||163|
1 Differences provided where statistically significant.
109. The association between dwelling characteristics and energy efficiency rating, as shown in Table 21, is strong. Across dwelling types, detached properties have the lowest energy efficiency profile on average (mean EER 59.9) while flats have the highest rating (67.7 for tenements and 66.6 for other flats).
110. The oldest, pre-1919, properties are least energy efficient (mean EER of 55.1 and only 16% rated C or better) while those built after 1982 have the highest energy efficiency ratings (mean of 71.0 and 69% in band C or better). The other age categories are comparable in terms of their energy efficiency profile.
Table 21: SAP 2012: Mean EER, Differences from 2015 and Broad EPC Band, by Dwelling Characteristics, 2016
|Mean||Differences from 2015 1||BC||DE||FG|
|Age of dwelling|
|Primary Heating Fuel|
1 Differences provided where statistically significant.
111. Primary heating fuel is a key determinant of the energy efficiency of the dwelling. Properties heated by mains gas have an average rating of 65.9 and 44% are in band C or better. Dwellings heated by other fuels (including electric and oil) have a considerably lower rating. The average energy efficiency rating for oil heated properties is 50.5 (making the average dwelling in this group E rated) and only 6% are in band C or better. Proximity to the gas grid has a similar effect on the energy efficiency rating. As dwelling characteristics associated with lower energy efficiency are disproportionately represented in rural areas, the average energy efficiency profile of rural properties tends to be lower than that for urban.
112. Improvements since 2015 which pass the statistical significance test include a 1.9 points gain in the mean SAP score for 1919-1944 dwellings and a 1.6 points gain for 1965-1982 dwellings. These improvements are reflected in the proportion of dwellings rated band B or C, which increased by eight percentage points since 2015 for both age categories. Smaller, but still significant improvements in the mean SAP score were measured for urban dwellings, and those on the gas grid. However, the corresponding increase of B and C rated dwellings for these categories was within the margin of error.
3.4 National Home Energy Ratings ( NHER)
113. 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 on how this emulated NHER score compares to previously published NHER figures can be found in the Methodology Notes to the 2013 SHCS report  .
114. Table 22 presents banded NHER scores and mean values for selected categories of dwellings and household types for 2016.
Table 22: NHER Scores and Banded Ratings by Selected Dwelling and Household Characteristics, 2016
|Dwelling Type (grouped)|
|Age of dwelling|
|Primary Heating Fuel|
|Other fuel type||7.6||66%||30%||4%||88|
3.5 Carbon Emissions
Based on modelled energy use, the average Scottish home is estimated to produce 7.0 tonnes of CO 2 per year. Average modelled carbon emissions for all properties have continued to decrease in the last year from 78 kg per square meter of floor area to 76 kg/m 2. Over the past year, there has been a reduction of 15% for post-1982 terraces from 67 kg/m 2 to 57 kg/m 2.
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 2010-2015.
117. In 2012, cooler temperatures led to an increase in domestic energy use and an increase in CO 2 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 CO 2 emissions. The SHCS estimates are not designed to capture the increased demand for heating due to colder weather in any particular year.
Table 23: Carbon Emissions and Modelled Emissions in Scottish Housing, 2010-2016
|Carbon Emissions 1: BEIS Domestic sector|
|per HH (tonnes) 2||5.8||5.0||5.4||5.1||4.3||4.1|
|% change per HH||6.1%||-13.0%||6.2%||-4.3%||-16.6%||-5.2%|
|Modelled emissions: SHCS|
|per HH ("t")||7.9||7.7||7.6||7.3||7.4||7.3||7.0|
|% change per HH||-||-2.6%||-1.4%||-3.6%||1.1%||-1.8%||-3.0%|
 Local and Regional CO 2 Emissions Estimates, BEIS. Data reflects revisions made in the most recent publication.
 Number of households ( HHs) sourced from National Records of Scotland, Estimates of Households and Dwellings, 2016: https://www.nrscotland.gov.uk/statistics-and-data/statistics/statistics-by-theme/households/household-estimates/2016
* Modelled emissions figures for 2014 to 2016 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 CO 2 equivalent figures which include the global warming impact of CH 4 and N 2O as well as CO 2.
121. The change in the underlying BREDEM 2012 model, first implemented in the reporting of 2014 data, has meant that carbon emissions for 2014-2016 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. As shown in Figure 14, 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).
Figure 14: Average Floor Area and Average Modelled Annual Emissions by Age and Type of Dwelling, 2016
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, 2016
|Dwelling Type||Dwelling Age|
|All dwelling types||9.7||6.6||5.9||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/m 2). Controlling for floor area in this way shows that pre-1919 detached houses have the highest modelled emissions per sq. m (106 kg/m² ), as shown in Table 25. Post-1982 terraces (57 kg/m 2), tenements (56 kg/m 2) and other flats (65 kg/m 2) have the lowest emissions.
Table 25: Average Modelled Emissions per Square Meter of Floor Area (kg/m 2) by Age and Type of Dwelling, 2016
|Dwelling Age||Pre-1919||1919-1982||Post-1982||All Ages|
3.5.2 Modelled Emissions by Tenure
126. Although data for 2014-2016 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/m 2 in 2010 to 80 kg/m 2 in 2013. Based on the updated carbon emissions methodology, there was then a further decrease from 80 kg/m 2 in 2014 to 76 kg/m 2 in 2016.
127. Figure 15 and Table 26 show how emissions differ across tenure for the period 2010 - 2016. The pattern of differences across tenure types has remained similar to previous years, with highest rates of emissions observed for the PRS (86 kg/m 2) and lowest for the HA sector (66 kg/m 2) and the remaining types of tenure with similar values in between.
128. Changes to the tenure definitions and the revised carbon emissions methodology mean that figures for 2014-2016 by tenure are not fully comparable to earlier years and most differences between years are not statistically significant. However, in the mortgaged sector average modelled emissions reduced from 78 kg/m 2 to 73 kg/m 2 and in housing association dwellings emissions fell from 71 kg/m 2 to 66 kg/m 2 between 2014 and 2016.
Table 26: Average Modelled Emissions per Square Meter by Tenure, 2010-2016*
Note: Data for 2010 to 2013 does not include households living rent free.
* Figures for 2014-2016 are therefore not fully comparable to previous years.
Figure 15: Modelled Emission per square meter (kg/m 2) by Tenure, 2010-2016*
Note: * Data for 2010 to 2013 does not include households living rent free. Figures for 2014-2016 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 and 2016, 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 trend in the median EIR between 2010 and 2016. This indicates that the environmental impact of Scottish housing is falling over time.
Figure 16: Median EIR relative to Band, 2010-2013 ( SAP 2009) and 2015-2016 ( SAP 2012)
132. As shown in Table 27 the proportion of dwellings with EI ratings in band C or better in 2016 was 29%. The mean rating was 59 which falls in band D.
133. In 2016, 10% of dwellings were rated F or G in terms of their environmental impact.
Table 27: EIR Bands in the Scottish Housing Stock, 2010-2013 and 2015-2016
|A - B (81+)||96||4%||102||4%||79||3%||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 2015-2016
135. Table 28 shows how EI ratings vary across different type of dwellings. As expected dwellings built more recently have better environmental impact ratings with 55% rated C or better and only 2% in the bottom two bands (F and G). Flats have 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, 2016
|Environmental Impact Rating||EI Band||Sample|
|Age of Dwelling|
|Primary Heating Fuel|
|Other fuel type||62.8||68%||9%||23%||88|