Scottish House Condition Survey: 2023 Key Findings

2 Energy Efficiency

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.

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 modelled 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 Methodological and Technical notes.

In this chapter we report on:

• levels of insulation in Scottish dwellings (section 2.1);
• boiler efficiencies (section 2.2);
• Energy Efficiency Ratings (EER), also known as SAP ratings (section 2.3);
• modelled carbon dioxide (CO2) emissions from dwellings (section 2.4); and
• Environmental Impact Ratings (EIR) (section 2.5).

A breakdown of findings is also provided by tenure of the household and other relevant dwelling characteristics.

2.1 Insulation Measures

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 achieve satisfactory levels of thermal comfort. (See Chapter 3 on Fuel Poverty).

Additional insulation is most commonly added to a property through the insulation of loft spaces, and by adding insulating material to external walls.

Key Points

• The majority of loft spaces are insulated. In 2023, loft insulation with a thickness of 100 mm or more had been installed in 96% of dwellings. This has been broadly stable since 2017 but represents an increase of 25 percentage points on 2007 levels.
• In 2023, 29% of lofts were insulated to a high standard of insulation (300 mm or more), similar to 2022 levels. The percentage of lofts with 300 mm or more insulation has remained around this level since 2014 following year on year increases from the 2010 figure of 5%.
• The proportion of insulated cavity walls recorded by the SHCS was 71% in 2023.
• The proportion of solid wall dwellings with insulation was 20% in 2023, an increase of around 9 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 69% in the social sector. In the private sector, 65% of lofts are insulated to 200 mm or more compared to 77% in the social sector.                                                    

2.1.1 Loft Insulation

The majority of loft spaces in Scotland are insulated.

Figure 2.1: Loft insulation (where applicable), 2003/2004 to 2023Description of figure 2.1

Figure 2.1 shows that since 2007, there has been an overall improvement in the uptake of loft insulation. The proportion of all applicable housing[1] with 100 mm or more of loft insulation has increased by around 25 percentage points on 2007 levels with 96% of applicable dwellings insulated to this degree in 2023. Most of this improvement occurred before 2014.

The share of dwellings with no loft insulation has fallen from 6% in 2003/4 to less than 0.5% in 2023. Most of this decline occurred before 2011. Since then, improvement has slowed down, suggesting that there may be barriers preventing the installation of insulation in the relatively few remaining uninsulated lofts.

Data Source: Table EE1 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 3]

In 2023, 29% of lofts were insulated to a high standard of insulation (300 mm or more), similar since 2014.

Figure 2.2: Depth of loft insulation (where applicable), 2003/2004 to 2023Description of figure 2.2

Since 2009 the thickness of loft insulation has notably increased. In 2023, 67% of dwellings with lofts had insulation with a depth of 200 mm or more compared to 27% in 2009. 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. The increase in the estimated number of dwellings with loft insulation of 200 mm or more between 2022 and 2023, is within the margin of error of the survey.

Data Source: Table EE1 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 3]

Levels of loft insulation are higher in the social sector than in the private sector.

Figure 2.3: Depth of loft insulation (where applicable) by tenure, 2003/2004 to 2023Description of figure 2.3

As shown in Figure 2.3 in 2023, 28% of private sector dwellings had a high standard (300 mm or more) of loft insulation, lower than 34% of dwellings in the social sector. 96% of private housing lofts were insulated to 100 mm or more and 65% to 200 mm or more. In the social sector, 99% of dwellings had lofts insulated to 100 mm or more, and 77% had 200 mm or more of loft insulation.

One of the reasons for the difference in uptake of loft insulation over time between the private and social sector is that the Scottish Housing Quality Standard (SHQS), which was introduced in 2004 and applies only to social sector housing, required dwellings to have of loft insulation if there was an appropriate loft space. (see section 5.2.3 for more information).

However, the difference in the proportion of lofts with 100 mm or more of insulation between the private and  social sectors has been reducing gradually, from 17 percentage points in 2003/04 (81% in the social and 64% in the private sector) to around 2 percentage points in 2023 (99% in the social sector and 96% in the private sector).

Data Source: Table EE2a in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 3]

2.1.2 Wall Insulation

The presence of cavity wall insulation (CWI) added since built is becoming increasingly difficult for SHCS surveyors to identify as over time the injection holes age, fade, or are covered up by later work. Additionally, contractors are also getting better at concealing their work. This may mean that the SHCS underestimates the number of homes which have had CWI installed (see section 6.2.2.4 of the 2019 SHCS key findings report). Therefore, despite efforts to maintain the high quality of the SHCS physical survey fieldwork, some misclassifications may remain.

In Scotland around 76% of dwellings (or around 1.93 million) have external cavity walls and the remaining 24% (or 609,000) have solid or other construction types of external wall. These “other” types may include steel, brick, block or dwellings made from prefabricated 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.

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 for the purposes of this report.

In 2023, 71% of cavity wall dwellings in Scotland were insulated.

Figure 2.4: Cavity wall insulation, 2012 to 2023Description of figure 2.4

In 2023, 71% of cavity wall dwellings in Scotland were insulated, similar to the level in 2014. The long term trend shows a decrease in the share of uninsulated cavity walls of around 5 percentage points between 2012 and 2014, but has remained fairly stable since then.

Data Source: Table EE3a in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 4]

In 2023, 20% of dwellings with solid and other wall types in Scotland were insulated.

Figure 2.5: Wall insulation of solid and other wall types, 2012 to 2023Description of figure 2.5

Figure 2.5 shows the levels of insulation in dwellings with solid or other construction type walls recorded by the survey from 2012 to 2023. The results show that 20% of dwellings in this category had insulated walls in 2023, similar to 2022, but a 10 percentage point increase from 2012. Only 778 dwellings with solid walls were surveyed in 2023 as part of the SHCS.

Data Source: Table EE3a in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 4]

The information in Table 2.1  breaks down the 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 2.6 of the Methodological and Technical notes).

HTTCs have certain attributes which make CWI more expensive, complex or inadvisable. Standard cavity walls have no such barriers.

Overall levels of wall insulation were higher in the social sector than in the private sector.

Table 2.1: Wall Insulation by wall type and tenure, 2023

Wall Type	Insulation Status	Wall/ Insulation Categories	Private Sector	Social Sector	All Tenures
Cavity	Un-insulated	HTTC wall	8%	11%	9%
Cavity	Un-insulated	Standard wall	21%	18%	20%
Cavity	Un-insulated	All	30%	29%	29%
Cavity	Insulated	CWI insulation	28%	34%	29%
Cavity	Insulated	Int/External insulation	4%	12%	6%
Cavity	Insulated	As built insulation	39%	25%	35%
Cavity	Insulated	All	70%	71%	71%
Cavity	All	All	100%	100%	100%
Solid/Other	Un-insulated	Pre-1919 wall	73%	27%	67%
Solid/Other	Un-insulated	Post-1919 wall	11%	21%	13%
Solid/Other	Un-insulated	All	85%	48%	80%
Solid/Other	Insulated	Retrofit insulation	13%	48%	17%
Solid/Other	Insulated	As built insulation	3%	4%	3%
Solid/Other	All Status	All	15%	52%	20%
Solid/Other	All	All	100%	100%	100%
All	Un-insulated	All	45%	31%	41%
All	Insulated	All	55%	69%	59%
All	All	All	100%	100%	100%
Cavity	All	Sample size (number)	1,737	636	2,373
Solid/Other	All	Sample size (number)	695	83	778
All	All	Sample size (number)	2,432	719	3,151

Around 69% of dwellings in the social sector had insulated walls, with 71% of cavity wall dwellings, and 52% of dwellings with solid and other wall types estimated to be insulated in 2023.

In the private sector, 70% of cavity wall dwellings and 15% of solid and other wall dwellings, had insulation in 2023. Over half (55%) of all private sector dwellings had insulated walls.

Overall, 71% of cavity wall dwellings in Scotland have wall insulation. 29% have had retrofit cavity wall insulation, which is generally the lowest cost improvement available; the remainder of insulated cavity walls were insulated as built (35%) or insulated in another way such as with internal and external wall insulation (6%).

Levels of insulation are higher in the social sector at 69% (all wall types) compared with 55% in the private sector. This is driven by higher levels of insulated solid walls in the social sector (52%) compared to the private sector (15%). Within wall type, this tenure divide is also apparent for more expensive insulation measures such as internal / external insulation of cavity walls (12% of cavity wall dwellings in the social sector; compared to 4% of private dwellings) and retrofit solid wall insulation measures 48% of solid wall dwellings in the social sector; versus 13% in the private sector).

Notes: [note 4]

2.2 Boilers

The heating system is a key factor in the thermal efficiency of a dwelling. Around 86% of households use a gas or oil-fuelled boiler (see Figure 1.7). 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.

Building regulations in Scotland effectively require the installation of a condensing boiler[2] for gas and oil-fuelled heating in new builds or when boilers are replaced in any dwelling.

In order to track the improved efficiency of gas and oil boilers associated with the rising standards of the regulatory framework the SHCS records the age of the household's heating system and contains sufficient data to derive the Seasonal Efficiency (SEDBUK) ratings of surveyed boilers.

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 1.4 of the Methodological and Technical notes.

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[3].

79% of gas and oil boilers met the minimum efficiencies specified by the current Building Standards, in 2023.

Figure 2.6: Gas and oil boiler types, 2012 to 2023Description of figure 2.6

In 2023 the survey found that 96% 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 around 15 percentage points since 2012. In 2023, 87% of gas and oil boilers were condensing boilers. This represents an increase of 49 percentage points since 2012. Around 79% of gas and oil boilers met the minimum efficiencies specified by the current Building Standards. This has increased substantially from 30% in 2012.

Data Source: Table EE5a in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

2.3 Energy Performance Certificates

Key Points

• In 2023, 56% of Scottish homes were rated as EPC band C or better under SAP 2012 (RdSAP v9.93), an increase of around 3 percentage points from 52% in 2022. The proportion of properties in the lowest EPC bands (E, F or G) under SAP 2012 (RdSAP v9.93), was 10% in 2023, down from 12% in 2022.
• Under SAP 2009, which allows for comparisons over a longer period, over half of dwellings (61%) were rated C or better, up 37 percentage points since 2010. In the same period, the proportion of properties in the lowest EPC bands (E, F or G) has reduced from 27% in 2010 to 8% in 2023.
• Under SAP 2009, the median EE rating in 2023 was 71, which is equivalent to Band C. This is an increase from 62 in 2010 which is equivalent to band D.

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 standardised energy usage. EPCs are required when a property is either sold or rented to a new tenant.

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.

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.

Ratings are adjusted for floor area so that they are essentially independent of dwelling size for a given built form.

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).

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 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 the assessment of existing buildings.

SHCS energy modelling for SAP 2012 in this report is based on RdSAP (v9.93). The 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 from 2018.

2.3.1 Energy Efficiency Rating, SAP 2009

This section examines the energy efficiency profile of the Scottish housing stock in 2023 under the SAP 2009 methodology.

Dwellings with main heating fuels other than mains gas (for example oil) 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.

The Scottish housing stock is gradually becoming more energy efficient.

Infographic 2.1: Mean and median EER relative to EPC bands, SAP 2009, 2010-2023 Description of infographic 2.1

Infographic 2.1 shows the trend in mean EERs based on SAP 2009, which rose from 59.9 in 2010 to 68.9 in 2023, going from band D to band C. There was around a 1-point increase in the mean EER each year between 2010 and 2014. Improvement since then has been slower, however the increase between 2022 and 2023 was 1.2 points.

The median EE Rating has also improved since 2010. In 2023, half of all Scottish dwellings were rated 71 or better, equal to EPC band C or above, an increase of 9 SAP points from 62 in 2010.

Data Source: Table EE6 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

A strong trend of improvement has been observed in the energy efficiency profile of the housing stock since 2010.

Figure 2.7: Distribution of the Scottish Housing Stock by EPC Band, SAP 2009, 2010-2023Description of figure 2.7

As shown in Figure 2.7, 61% of the housing stock in 2023 had an EPC rating of C or better, up 37 percentage points since 2010. Over the same period, the proportion of properties in the lowest EPC bands, E, F and G, has dropped around 20 percentage points: 27% of properties were rated E, F or G in 2010 compared with 8% in 2023.

Data Source: Table EE7a in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 5]

2.3.2 Energy Efficiency Rating, SAP 2012

This section examines the energy efficiency profile of the Scottish housing stock under the SAP 2012 methodology (RdSAP v9.93) with time series analysis is presented from 2018. Further breakdowns by household and dwelling characteristics for 2023 are also presented.

The Scottish housing stock is gradually becoming more energy efficient.

Infographic 2.2: Mean and median EER relative to EPC bands, SAP 2012, 2010-2023 

Description of infographic 2.2

In 2023, the mean energy efficiency rating of the Scottish housing stock under SAP 2012 (RdSAP v9.93) was 67.7 and the median was 69 points. The mean rating increased between 2022 and 2023, from 66.6 to 67.7.

Data Source: Table EE6 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Scottish housing is gradually moving up through the EPC bands.

Figure 2.8: Distribution of the Scottish Housing Stock by EPC Band, SAP 2012, 2018-2023Description of figure 2.8

Figure 2.8 shows that 56% of all properties in 2023 were rated C or better under SAP 2012 (RdSAP v9.93), an increase of around 3 percentage points from 52% in 2022. 10% of properties in 2023 were in bands E, F or G, down from 12% in 2022.

Data Source: Table EE7a in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 5]

Housing in the social sector tends to be more energy efficient than the owner occupied or private rented sector.

Figure 2.9: Percentage of dwellings by EPC band and tenure in 2023   Description of figure 2.9

As shown in Figure 2.9, 69% of social housing is in band C or better under SAP 2012 (RdSAP v9.93). Higher than both the private rented sector at 52% and the owner-occupied sector at 51%. Around 5% of dwellings in the social sector are within EPC bands E, F or G, while 11% of owner occupied dwellings and 14% of the private rented sector are within these EPC bands. These differences could be driven by the Scottish Housing Quality Standard (SHQS) and the Energy Efficiency Standard for Social Housing (EESSH) which introduced minimum energy efficiency levels for the social sector.

Data Source: Table EE8a in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Across Scotland, 3% of properties were in bands F or G in 2023.

Figure 2.10: Proportion of homes in EPC Band F or G by dwelling and household characteristics, SAP 2012 v9.93Description of figure 2.10

Figure 2.10 shows that dwellings in the lowest energy efficiency bands (F and G) are more likely to be older pre-1919 dwellings (9%), non-gas heated properties (10% for electric, 20% for oil and 8% for other fuels), detached properties (6%), off gas grid properties (17%), and in rural areas (11%). Across Scotland as a whole, 3% of properties were in bands F or G in 2023.

Data Source: Table EE9 and EE10 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 1] [note 2] [note 4]

There is a strong association between tenure and mean energy efficiency rating.

Table 2.2: Mean EER and percentage in EPC bands ABC, by household characteristics in 2023, SAP 2012

Household Characteristics	Category	SAP 2012 Ratings Mean	EPC Band ABC (%)
Tenure	Owned outright	65.3	45%
Tenure	Mortgaged	69.3	59%
Tenure	LA	69.4	63%
Tenure	HA	72.8	78%
Tenure	Private rented	65.6	52%
Tenure (grouped)	Private Sector	66.7	51%
Tenure (grouped)	Social Sector	70.9	69%
Household Composition	Older Households	66.1	50%
Household Composition	Families	69.3	61%
Household Composition	Other Households	68.3	57%
Annual Household Income	< £15,000	68.4	58%
Annual Household Income	£15,000 - £24,999	67.7	57%
Annual Household Income	£25,000 - £34,999	67.5	55%
Annual Household Income	£35,000 - £44,999	66.5	51%
Annual Household Income	£45,000+	68.2	57%
Council Tax Band	Band A	67.7	59%
Council Tax Band	Band B	67.4	53%
Council Tax Band	Band C	68.0	58%
Council Tax Band	Band D	68.6	59%
Council Tax Band	Band E	67.0	51%
Council Tax Band	Band F	68.4	57%
Council Tax Band	Band G & H	67.2	51%
All households	All households	67.7	56%

Mean SAP 2012 (RdSAP v9.93) ratings ranged from 65.3 in dwellings owned outright to 72.8 in housing association dwellings, a statistically significant difference. Furthermore, social housing as a whole is more energy efficient than the private sector, with a mean EER of 70.9 compared to 66.7 for private dwellings.

Older households (66.1) have lower average EER ratings than families (69.3) and other (adults without children) households (68.3).

For more information and sample sizes, please see Table EE9 and EE10 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

There is a strong association between dwelling characteristics and energy efficiency rating.

Table 2.3: Mean EER and percentage in EPC bands ABC, by dwelling characteristics in 2023, SAP 2012

Dwelling Characteristics	Category	SAP 2012 Ratings Mean		EPC Band ABC (%)
Dwelling Type	Detached	65.1		48%
Dwelling Type	Semi-detached	65.8		44%
Dwelling Type	Terraced	66.8		52%
Dwelling Type	Tenement	71.1		68%
Dwelling Type	Other flats	71.0		71%
Dwelling Age	pre-1919	60.2		29%
Dwelling Age	1919-1944	65.5		45%
Dwelling Age	1945-1964	66.2		48%
Dwelling Age	1965-1982	66.9		52%
Dwelling Age	post-1982	74.8		83%
Primary Heating Fuel	Gas	69.9		62%
Primary Heating Fuel	Oil	51.8		10%
Primary Heating Fuel	Electric	60.2		33%
Primary Heating Fuel	Other fuel type	65.0		58%
Urban-Rural Indicator	Urban	69.2		60%
Urban-Rural Indicator	Rural	60.4		36%
Gas Grid	On grid	69.4		60%
Gas Grid	Off grid	54.9		23%
All dwellings	All dwellings	67.7		56%

Table 2.3 shows that across dwelling types, detached properties have the lowest energy efficiency ratings on average (mean EER 65.1) while flats have the highest ratings (71.1 for tenements and 71.0 for other flats).

The oldest, pre-1919, properties are the least energy efficient (mean EER of 60.2 and 29% rated C or better) while those built after 1982 have the highest energy efficiency ratings (mean EER of 74.8, with 83% in band C or better).

Primary heating fuel is a key determinant of the energy efficiency rating of the dwelling. Properties heated by mains gas have an average EER rating of 69.9 and 62% are in band C or better. Dwellings heated by other fuels (including electric and oil) have considerably lower ratings by comparison. The average energy efficiency rating for oil heated properties is 51.8 (corresponding to EPC band E) and only 10% are in band C or better. For electric heated dwellings the average energy efficiency rating was 60.2 with 33% in band C or better. 

Proximity to the gas grid has a similar effect on the energy efficiency rating. Dwellings on the gas grid have an average SAP rating of 69.4, higher than the average SAP rating of 54.9 for off grid 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 areas. Table 2.3 shows that the mean SAP 2012 (RdSAP v9.93) rating is 69.2 for dwellings in urban areas with 60% in band C or above. Higher than the mean rating of 60.4 for dwellings in rural areas, where 36% of dwellings are in band C or better.

For more information and sample sizes, please see Table EE9 and EE10 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 1] [note 2] [note 4]

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. Further details can be found in the Methodology Notes to the 2013 SHCS report. However because of user interest (and because NHER scores were previously taken into account under the energy efficiency criterion of the SHQS) we provide an approximate NHER score by household and dwelling characteristics in Table EE11 and EE12 in ‘SHCS 2022- Chapter 02 Energy Efficiency- tables and figures’.

2.4 Carbon Emissions

Key Points

• Based on the modelled energy use required to meet the SAP standard heating regime[4], the average Scottish home was estimated to produce 6.3 tonnes of carbon dioxide (CO2) per year in 2023, which is more than double the average carbon emissions per household as reported by Department for Energy Security and Net Zero (2.9 tonnes per year) in 2022, based on actual energy use. This suggests that households are not heating their homes to the SAP standard heating regime.
• Average modelled carbon emissions for all properties were 67 kg per square meter of floor area in 2023.

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 Department for Energy Security and Net Zero in the Local and Regional Carbon Dioxide (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.

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 cost, preferences or changes in weather conditions. As such, they are distinct from the carbon emissions figures published by Department for Energy Security and Net Zero and compiled in GHG inventories.

Estimates in the Climate Change Plan: Third Report on Proposals and Policies (RPP3) 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. 

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  section 1.3 of the Methodological and Technical notes.

To derive emissions estimates, modelled energy demand is combined with carbon intensity factors as adopted for the 2012 edition of the SAP (see section 1.3 of the Methodological and Technical notes). These are carbon dioxide (CO2) equivalent figures which include the global warming impact of methane (CH4) and nitrous oxide (N2O) as well as carbon dioxide (CO2).

2.4.1 Modelled Emissions by Dwelling Type and Age of Construction

The annual modelled emissions from a property reflect the energy use for the whole dwelling heated according to the SAP standard heating regime[5].

Newer dwellings have lower modelled emissions than older ones.

Table 2.4: Modelled annual carbon emissions by dwelling age and type, 2023

Dwelling Age	Dwelling Type	Carbon Emissions (tonnes/ year)
Pre-1919	Detached	15.9
Pre-1919	Semi-detached	11.1
Pre-1919	Terraced	8.4
Pre-1919	Tenement	5.3
Pre-1919	Other flats	7.9
Pre-1919	All dwellings	9.0
1919-1982	Detached	9.4
1919-1982	Semi-detached	6.6
1919-1982	Terraced	5.8
1919-1982	Tenement	4.3
1919-1982	Other flats	4.3
1919-1982	All dwellings	6.0
Post-1982	Detached	7.2
Post-1982	Semi-detached	4.7
Post-1982	Terraced	4.5
Post-1982	Tenement	3.3
Post-1982	Other flats	2.8
Post-1982	All dwellings	5.1
All Dwelling ages	Detached	9.4
All Dwelling ages	Semi-detached	6.7
All Dwelling ages	Terraced	5.9
All Dwelling ages	Tenement	4.2
All Dwelling ages	Other flats	4.6
All Dwelling ages	All dwelling types	6.3

Table 2.4 shows that on average newer dwellings have lower modelled emissions than older ones, likely as a result of their better thermal performance and higher energy efficiency (as shown in section 2.3). Post-1982 tenement and other flats have the lowest modelled emissions on average (3.3 and 2.8 tonnes per year, respectively).

Across all age bands, detached houses have the highest modelled emissions due to a larger share of exposed surfaces (between 15.9 tonnes per year for pre-1919 dwellings to 7.2 tonnes per year for post-1982 dwellings). As shown in section 1.3 of this report, they are also the most likely to use high carbon-intensity fuels such as oil in place of mains gas.

For more information, please see Table EE14 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Older dwellings have higher modelled carbon emissions per square meter of floor area

Table 2.5: Modelled annual carbon emissions (per square meter of floor area) by dwelling age and type, 2023

Dwelling Age	Dwelling Type	Carbon Emissions (kg/sqm)
Pre-1919	Detached	104
Pre-1919	Semi-detached	86
Pre-1919	Terraced	78
Pre-1919	Tenement	74
Pre-1919	Other flats	72
Pre-1919	All dwellings	82
1919-1982	Detached	73
1919-1982	Semi-detached	75
1919-1982	Terraced	70
1919-1982	Tenement	68
1919-1982	Other flats	63
1919-1982	All dwellings	70
Post-1982	Detached	52
Post-1982	Semi-detached	55
Post-1982	Terraced	55
Post-1982	Tenement	51
Post-1982	Other flats	51
Post-1982	All dwellings	53
All Dwelling ages	Detached	68
All Dwelling ages	Semi-detached	71
All Dwelling ages	Terraced	68
All Dwelling ages	Tenement	64
All Dwelling ages	Other flats	62
All Dwelling ages	All dwelling types	67

Older dwellings tend to be larger, thus generally having greater heat requirements and energy use (see section 1.2). When analysing emissions we control for this by dividing modelled emissions by total internal floor area, to derive carbon dioxide (CO2) emissions per square meter (kg/m2). Controlling for floor area in this way (Table 2.5) shows that in general older dwellings have higher emissions per square meter than newer dwellings of equivalent type, as well as higher emissions overall. For example pre-1919 detached houses have the higher modelled emissions per square meter (104 kg/m²) than detached 1919-1982 dwellings (73 kg/m²) and post 1982 detached dwellings (52 kg/m²). Post-1982 dwellings have the lowest emissions of any age band, particularly tenements (51 kg/m2) and other flats (51 kg/m2), which have lower emissions per meter square than post 1982 houses.

For more information, please see Table EE14 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’.

2.4.2 Modelled Emissions by Tenure

Although data for 2014-2023 is not directly comparable to prior years due to changes in the carbon emissions methodology, 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 followed by a reduction to 69 kg/m2 in 2022 and to 67 kg/m2 in 2023.

Private rented sector dwellings have higher overall modelled carbon emissions than other tenure types.

Figure 2.11: Average modelled emissions by tenure, 2010 to 2023Description of figure 2.11

Figure 2.11 shows how emissions differ across tenure for the period 2010 to 2023. In 2023, the highest emissions were observed for private rented sector dwellings (77 kg/m2) and lowest for housing association dwellings (61 kg/m2). The values were similar to the previous year across all tenures; however, the longer time series shows a decreasing trend over the 2010-2023 period for all tenures. 

Changes to the tenure definitions[6] and the revised carbon emissions methodology mean that figures for 2014 to 2023 by tenure are not fully comparable to earlier years. Differences that were statistically significant were seen in all sectors when looking at the longer time series; most notable are in mortgaged sector (reducing from 78 kg/m2 in 2014 to 62 kg/m2 in 2023) and in households that are owned outright (reducing from 81 kg/m2 to 68 kg/m2 between 2014 and 2023). Similarly, carbon emission values reduced in the private rented sector from 89 kg/m2 in 2014 to 77 kg/m2 in 2023, in HA dwellings from 71 kg/m2 in 2014 to 61 kg/m2 in 2023 and in LA dwellings from 77 kg/m2 in 2014 to 69 kg/m2 in 2023.

Data Source: Table EE15 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 6]

2.5 Environmental Impact Rating

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 the SAP methodology.

EIRs for 2023 have been described in this report based on SAP 2012 under RdSAP v9.93. 

The Environmental Impact Rating (EIR) of Scottish dwellings has gradually increased over time.

Infographic 2.3: Median EIR relative to Band, 2018 to 2023.Description of infographic 2.3

In 2023, the mean EIR rating was 64 and the median was 67, both of which fall in band D. Infographic 2.3 illustrates the increasing trend in the mean and median EIR between 2018 and 2023. This indicates that the environmental impact of Scottish housing is gradually falling over time but has remained within band D.

Data Source: Table EE16 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

In 2023, 43% of dwellings had an EIR of band C or above

Figure 2.12: EIR Bands in the Scottish Housing Stock, 2018 – 2023, SAP 2012Description of figure 2.12

As shown in Figure 2.12, 43% of dwellings had EI ratings in band C or better under SAP 2012 (RdSAP v9.93) in 2023, an improvement on the 2019 figure of 34%. In 2023 20% of dwellings were rated E, F or G in terms of their environmental impact, similar to the 2022 rate of 23% but lower than 2019 rate of 27%.

Data Source: Table EE16 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Environmental Impact Ratings (EIRs) vary across different type of dwellings.

Table 2.6: Mean EIR and percentage in EIR Bands ABC, by dwelling characteristics, 2023

Dwelling Characteristics	Category	EIR (Mean)	EIR Band ABC (%)
Dwelling Type	House	61.4	33%
Dwelling Type	Flat	69.2	61%
Dwelling Age	pre-1919	54.6	21%
Dwelling Age	1919-1944	60.8	31%
Dwelling Age	1945-1964	62.1	32%
Dwelling Age	1965-1982	63.3	36%
Dwelling Age	post-1982	73.4	73%
Primary Heating Fuel	Gas	67.2	48%
Primary Heating Fuel	Oil	42.9	3%
Primary Heating Fuel	Electric	52.2	21%
Primary Heating Fuel	Other fuel type	64.8	70%
Urban-Rural Indicator	Urban	66.0	46%
Urban-Rural Indicator	Rural	55.2	28%
Gas Grid	On grid	66.2	46%
Gas Grid	Off grid	48.9	20%
All dwellings	All dwellings	64.2	43%

Dwellings built post-1982 have (higher) better EIRs than other dwellings, with 73% rated band C or better. Flats have a lower environmental impact (higher EIR) than houses, as do gas heated properties compared to those heating using oil or electricity.

Oil heating systems and houses are more common in rural areas, leading to higher environmental impacts (lower EIRs) for rural dwellings. Dwellings near the gas grid have better EIRs than dwellings off the gas grid, with 46% of dwellings on the gas grid rated band C or better compared to 20% for dwellings off the gas grid.

This is likely due to gas having a lower emissions factor (0.216 kg of carbon dioxide per kilowatt hour) than electricity (0.519) in the underlying SAP methodology used in this report. See table 1.5 in the Technical and Methodological notes for a full list of emissions factors used.

For more information and sample sizes, please see Table EE17 in ‘SHCS 2023- Chapter 02 Energy Efficiency- tables and figures’

Notes: [note 1] [note 2]