Scottish House Condition Survey: 2021 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 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.

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).

When interpreting and using the results presented in this chapter, readers should be mindful of the impact the external+ approach used for the 2021 SHCS has had on data quality. This is discussed in detail in Chapter 6 of this report.

In particular, readers should note that the results on EERs/SAP ratings have likely been impacted by the change in the mode of data collection (and approach).

It is likely that EERs have been overestimated due to mode effects associated with the 2021 external+ SHCS. Surveyors were reliant on householders providing information via telephone that would normally be collected as part of the internal dwelling inspection. There appears to have been a particular problem resulting in an overestimate of the proportion of dwellings with 100% fixed low-energy lighting, which will then result in EERs being overestimated. It is likely that the non-response bias in the 2021 SHS and SHCS samples will also have contributed. For further details see section 6.5.3 of this report.

 

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 enjoy 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 2021, loft insulation with a thickness of 100 mm or more had been installed in 94% of dwellings which had a loft.
• In 2021, 27% of lofts were insulated to a high depth of insulation (300 mm or more).
• The proportion of insulated cavity walls recorded by the SHCS was 72% in 2021.
• The proportion of solid wall dwellings with insulation was 17% in 2021.
• 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, 62% of lofts are insulated to a depth of 200 mm or more compared to 73% in the social sector.     

2.1.1 ​​​​Loft Insulation

In SHCS 2021, the proportion of dwellings without loft spaces was 24%.

Figure 2.1: Depth of Loft Insulation (all dwellings, including those with no loft space), 2021

Data Source: Table EE1 in 'Energy Efficiency' tables

The proportion of all applicable housing with no loft insulation was 1%, in 2021. 93% of dwellings with lofts were insulated to a depth of 100 mm or more and 64% of dwellings with lofts were insulated to a depth of 200 mm or more (see Table 2.1)

Table 2.1: Depth of Loft Insulation (where applicable), 2021 [note 1] [note 5]

Loft Insulation	Percentage of dwellings (%)	Number of dwellings (thousands)
Not insulated	1%	23
1mm-99mm	6%	107
100mm-199mm	29%	564
200mm or more	64%	1,221
All Dwellings	100%	1,915
Sample size (number)	2,518

The percentage of lofts with a high depth of insulation (300 mm or more) was 27% in 2021. 26% of private sector dwellings had a high depth of loft insulation, lower than 35% of dwellings in the social sector (see Table 2.2).

As shown in Table 2.2 the depth of loft insulation is greater in social sector dwellings than private sector dwellings. In 2021, 93% of lofts in the private sector were insulated to a depth of 100 mm or more and 62% to a depth of at least 200 mm. In the social sector, 95% of dwellings had lofts insulated to a depth 100 mm or more, and 73% had at least 200 mm of loft insulation.

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.

Table 2.2: Depth of Loft Insulation, 2021 [note 1] [note 4] [note 6]

Loft Insulation	Private Sector	Social Sector	All Tenures
none	2%	[w]	1%
1mm - 99mm	6%	5%	6%
100mm - 199mm	31%	23%	30%
200mm - 299mm	36%	38%	37%
300mm or more	26%	35%	27%
Total	100%	100%	100%
Sample size (number)	2,090	428	2,518

As surveyors were unable to enter dwellings to inspect loft spaces for the presence and depth of insulation, households were sent a letter in advance of the surveyor appointment asking them to record the average depth of any loft insulation. This was then provided to surveyors by telephone. This may have impacted on the quality of this data. However it should be noted that the profile of the housing stock by depth of loft insulation, though not directly comparable, was similar to previous years (see Table DQ9 in the external+ data quality tables accompanying this report).

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. 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 also section 6.2.2.4 of the 2019 SHCS key findings report). Despite efforts to maintain the high quality of the SHCS physical survey fieldwork, some misclassifications may remain.

In Scotland around 60% of dwellings have external cavity walls and the remaining 40% 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.

Table 2.3 shows the proportion of insulated dwellings by type of 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.

In 2021, 72% of cavity wall dwellings in Scotland were insulated (see Table 2.3). 

Table 2.3: Wall Insulation by Wall Type, 2021 [note 1] [note 4] [note 6]

Insulation Status	Cavity Wall	Solid/Other Wall	All Wall Types
Un-insulated	28%	83%	42%
Insulated	72%	17%	58%
Total	100%	100%	100%
Sample size (number)	2,330	844	3,174

Table 2.3 shows that 17% of dwellings with solid or other construction type walls had insulated walls in 2021.

The information in Table 2.4 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 7.6.6).

HTTCs have certain attributes which make CWI more expensive, complex or inadvisable. Standard cavity walls have no such barriers. It should be noted that HTTCs may be underestimated in this report. The presence of rising or penetrating damp is used to identify HTTCs and no information on the presence of this was collected due to the enforced methodological changes for the 2021 SHCS (see Chapter 6).

Table 2.4: Wall Insulation by Wall Type and Tenure, 2021 [note 1] [note 4] [note 6]

Wall Type	Insulation Status	Wall/ Insulation Categories	Private Sector	Social Sector	All Tenures
Cavity	Un-insulated	HTTC wall	8%	10%	8%
Cavity	Un-insulated	Standard wall	21%	13%	19%
Cavity	Un-insulated	All wall categories	29%	24%	28%
Cavity	Insulated	CWI insulation	33%	39%	34%
Cavity	Insulated	Int/External insulation	4%	14%	7%
Cavity	Insulated	As built insulation	35%	24%	32%
Cavity	Insulated	All insulation categories	71%	76%	72%
Cavity	All Insulation Status	All categories	100%	100%	100%
Solid/Other	Un-insulated	Pre-1919 wall	76%	36%	70%
Solid/Other	Un-insulated	Post-1919 wall	11%	26%	13%
Solid/Other	Un-insulated	All wall categories	87%	61%	83%
Solid/Other	Insulated	Retrofit insulation	11%	37%	14%
Solid/Other	Insulated	As built insulation	3%	1%	2%
Solid/Other	All Insulation Status	All insulation categories	13%	39%	17%
Solid/Other	All Insulation Status	All categories	100%	100%	100%
All Wall Types	Un-insulated	All wall categories	45%	30%	42%
All Wall Types	Insulated	All insulation categories	55%	70%	58%
All Wall Types	All Insulation Status	All categories	100%	100%	100%
Cavity	All Insulation Status	Sample size (number)	1,408	482	1,890
Solid/Other	All Insulation Status	Sample size (number)	1,115	169	1,284
All Wall Types	All Insulation Status	Sample size (number)	2,523	651	3,174

In the social sector, 76% of cavity wall dwellings and 39% of dwellings with solid and other wall types were found to be insulated in 2021. 70% of social housing overall had insulated walls.

In the private sector, 71% of cavity wall dwellings and 13% of solid and other wall dwellings, had insulation in 2021. Over half (55%) of all private sector dwellings had insulated walls.

Overall 72% of cavity wall dwellings in Scotland have wall insulation. 34% have had retrofit cavity wall insulation, which is generally the lowest cost improvement available; the remainder of insulated cavity walls were insulated as built (32%) or insulated in another way such as with internal and external wall insulation (7%).

Levels of insulation are higher in the social sector at 70% (all wall types) compared with 55% in the private sector.  This is being driven by higher levels of insulated solid walls in the social sector (39%) compared to the private sector (13%). 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; 4% of private dwellings) and retrofit solid wall insulation measures (37% of solid wall dwellings in the social sector; 11% in the private sector).

 

2.2 Boilers

Key Points

• In 2021, 66% of gas and oil boilers met the minimum efficiencies specified by the current Building Standards.

The heating system is a key factor in the thermal efficiency of a dwelling. Around 88% of households use a gas or oil-fuelled boiler (see Table 1.4). 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 [3] for gas and oil-fuelled heating in new builds or when boilers are replaced in any dwelling.

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 [4].

Table 2.5: Gas and Oil Boiler Types, 2021 [note 1] [note 4]

Boiler Type	Percentage of dwellings (%)	Number of dwellings (thousands)
Post-1998 Boilers	96%	2,111
Condensing Boilers	80%	1,752
Standards Compliant Boilers	66%	1,444
Sample size (number)	2,661

The proportion of households using gas or oil boilers for heating is available on Table KA6a in the 'Key Attributes of the Scottish Housing Stock' tables.

In 2021 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 (see Table 2.5).

Table 2.5 shows that 80% of gas and oil boilers were condensing boilers.

In 2021, 66% of gas and oil boilers met the minimum efficiencies specified by the current Building Standards (see Table 2.5).

As surveyors were unable to enter dwellings to record the make and model of the boiler, households were sent a letter in advance of the surveyor appointment asking them to make a note of this. This was then provided to surveyors by telephone. This may have impacted on the quality of this data. However it should be noted that the percentage of boilers by age and type and the percentage complaint with minimum standards, though not directly comparable, was similar to previous years (see Table DQ9 in the external+ data quality tables accompanying this report).

 

2.3 Energy Performance Certificates

Key Points

• In 2021, 52% of Scottish homes were rated as EPC band C or better under SAP 2012 (RdSAP v9.93).
• The proportion of properties in the lowest EPC bands (E, F or G) was 13% in 2021.
• The median energy efficiency rating was 70, corresponding to EPC band C.

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 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 the SAP 2012 methodology.

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.

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

 2.3.1 Energy Efficiency Rating, SAP 2012

This section examines the energy efficiency profile of the Scottish housing stock in 2021 under the SAP 2012 methodology (RdSAP v9.93).

Table 2.6 and Table 2.7 show the energy efficiency profile of the Scottish housing stock in 2021 under SAP 2012 (RdSAP v9.93).

Table 2.6: Average EER for 2021, SAP 2012 (RdSAP v9.93)

Energy Efficiency Rate (EER)	2021
Mean	67.9
Median	70.0
Sample size (number)	3,174

In 2021, the mean energy efficiency rating of the Scottish housing stock under SAP 2012 (RdSAP v9.93) was 67.9 and the median was 70 points, indicating that half of the housing stock has an energy efficiency rating of 70 or better (Table 18).

52% of all properties in 2021 were rated C or better under SAP 2012 (RdSAP v9.93) and 13% were in bands E, F or G (see Table 2.7).

Table 2.7: Distribution of the Scottish Housing Stock by EPC Band in 2021, SAP 2012 (RdSAP v9.93)  [note 1] [note 4]

EPC Band	Percentage of dwellings (%)	Number of dwellings (thousands)
A (92-100)	[low]	2
B (81-91)	5%	121
C (69-80)	47%	1,185
D (55-68)	35%	896
E (39-54)	10%	248
F (21-38)	3%	66
G (1-20)	[low]	11
All EPC Bands	100%	2,529
Sample size (number)	3,174

Table 2.8 shows the energy efficiency profile by broad tenure groups in 2021 using SAP 2012 (RdSAP v9.93). Figure 2.2 provides more details on the distribution of the least energy efficient properties by household characteristics.

Table 2.8: Percentage of dwellings by EPC band and tenure in 2021  [note 1] [note 4]

EPC band	Owner occupied (%)	Private rented (%)	Social sector (%)	All Tenures (%)
A (92-100)	[low]	[w]	[low]	[low]
B (81-91)	4%	7%	6%	5%
C (69-80)	43%	44%	59%	47%
D (55-68)	38%	35%	28%	35%
E (39-54)	11%	9%	6%	10%
F (21-38)	3%	5%	1%	3%
G (1-20)	[low]	1%	[w]	[low]
Total	100%	100%	100%	100%
Sample size (number)	2,100	423	651	3,174

65% of social housing is in band C or better under SAP 2012 (RdSAP v9.93), compared to 51% in the private rented sector and to 47% in the owner-occupied sector. 7% of dwellings in the social sector are within EPC bands E, F or G, while 14% of owner occupied dwellings and 15% 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.

Figure 2.2 shows that the share of dwellings in the lowest energy efficiency bands (F and G) is particularly high for pre-1919 dwellings (9%), non-gas heated properties (between 11% for electric and 18% for oil), detached properties (7%), off gas grid properties (19%), rural areas (12%) and in the private rented stock (6%). Across Scotland as a whole, 3% of properties were in bands F or G in 2021.

Figure 2.2: Proportion of Homes in EPC Band F or G by Dwelling and Household Characteristics in 2021, SAP 2012 (RdSAP v9.93) [note 2] [note 3]

Data Source: Tables EE10 and EE11 in 'Energy Efficiency' tables.

More detailed breakdowns are shown in Table 2.9 by household characteristics and in Table 2.10 by dwelling characteristic.

Mean SAP 2012 (RdSAP v9.93) ratings ranged from 64.2 in dwellings owned outright to 71.4 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 69.9 compared to 65.5 for private dwellings.

Older households (63.9) have lower average EER ratings than families (68.3) and other (adults without children) households (67.7).

Mean EER ratings ranged from 65.8 to 67.0 across income bands. Average EER ratings ranged from 63.1 to 67.5 across council tax bands with dwellings in higher council tax bands being less energy efficient.

Table 2.9: Mean EER and Broad EPC Band, by Household Characteristics in 2021, SAP 2012 (RdSAP v9.93)

Household Characteristics	Category	SAP 2012 (RdSAP v9.93) Ratings - Mean	EPC Band ABC (%)	EPC Band DE (%)	EPC Band FG (%)
Tenure	Owned outright	64.2	43%	53%	4%
Tenure	Mortgaged	67.6	54%	44%	2%
Tenure	LA	68.9	59%	41%	[low]
Tenure	HA	71.4	75%	24%	1%
Tenure	Private rented	65.7	51%	44%	6%
Tenure (grouped)	Private Sector	65.5	48%	49%	4%
Tenure (grouped)	Social Sector	69.9	65%	34%	1%
Household Composition	Older Households	63.9	43%	52%	5%
Household Composition	Families	68.3	55%	44%	1%
Household Composition	Other Households	67.7	57%	40%	3%
Annual Household Income	< £15,000	65.8	48%	48%	4%
Annual Household Income	£15,000 - £24,999	66.4	54%	43%	3%
Annual Household Income	£25,000 - £34,999	67	53%	45%	2%
Annual Household Income	£35,000 - £44,999	66.9	50%	48%	3%
Annual Household Income	£45,000+	66.7	52%	45%	3%
Council Tax Band	Band A	67.5	59%	38%	2%
Council Tax Band	Band B	66.2	50%	47%	3%
Council Tax Band	Band C	67.1	53%	46%	2%
Council Tax Band	Band D	67.4	55%	41%	4%
Council Tax Band	Band E	65.7	47%	50%	3%
Council Tax Band	Band F	66.7	48%	51%	1%
Council Tax Band	Band G & H	63.1	42%	51%	7%
All households	All households	66.5	52%	45%	3%

Sample sizes are available on Table EE10 in 'Energy Efficiency' tables.

Table 2.10 shows that there is a strong association between dwelling characteristics and energy efficiency rating. Across dwelling types, detached properties have the lowest energy efficiency ratings on average (mean EER 62.8) while flats have the highest ratings (70.3 for tenements and 68.7 for other flats).

The oldest, pre-1919, properties are the least energy efficient (mean EER of 58.9 and 30% rated C or better) while those built after 1982 have the highest energy efficiency ratings (mean EER of 73.2, with 79% in band C or better).

Primary heating fuel is a key determinant of the energy efficiency of the dwelling. Properties heated by mains gas have an average rating of 68.9 and 58% are in band C or better. Dwellings heated by other fuels (including electric and oil) have considerably lower ratings. The average energy efficiency rating for oil heated properties is 50.9 (corresponding to EPC band E) and only 8% are in band C or better. For electric heated dwellings the average energy efficiency rating was 58.6 and 32% are in band C or better.  

Proximity to the gas grid has a similar effect on the energy efficiency rating (average SAP rating 68.0 for dwellings near the gas grid, higher than the 59.4 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 2.10 shows that the mean SAP 2012 (RdSAP v9.93) rating is 68.3 for dwellings in urban areas, higher than the 57.7 for dwellings in rural areas, where 29% of dwellings are in band C or better.

Table 2.10: Mean EER and Broad EPC Band, by Dwelling Characteristics in 2021, SAP 2012 (RdSAP v9.93) [note 2] [note 4]

Dwelling Characteristics	Category	SAP 2012 (RdSAP v9.93) Ratings - Mean	EPC Band ABC (%)	EPC Band DE (%)	EPC Band FG (%)
Dwelling Type	Detached	62.8	43%	49%	7%
Dwelling Type	Semi-detached	65.5	41%	58%	1%
Dwelling Type	Terraced	66.1	46%	53%	2%
Dwelling Type	Tenement	70.3	69%	29%	2%
Dwelling Type	Other flats	68.7	64%	35%	1%
Dwelling Age	pre-1919	58.9	30%	61%	9%
Dwelling Age	1919-1944	64.9	40%	58%	2%
Dwelling Age	1945-1964	65.8	43%	55%	2%
Dwelling Age	1965-1982	66.4	50%	47%	3%
Dwelling Age	post-1982	73.2	79%	20%	[low]
Primary Heating Fuel	Gas	68.9	58%	42%	1%
Primary Heating Fuel	Oil	50.9	8%	73%	18%
Primary Heating Fuel	Electric	58.6	32%	56%	11%
Primary Heating Fuel	Other fuel type	60.1	44%	42%	14%
Urban-Rural Indicator	Urban	68.3	56%	42%	1%
Urban-Rural Indicator	Rural	57.7	29%	60%	12%
Gas Grid	On grid	68.5	57%	42%	1%
Gas Grid	Off grid	52	15%	66%	19%
All dwellings	All dwellings	66.5	52%	45%	3%

Sample sizes are available on Table EE11 in 'Energy Efficiency' tables.

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 taken into account under the energy efficiency criterion of the SHQS) we provide an approximate NHER score by household and dwelling characteristics in Table EE12 and EE13 in 'Energy Efficiency' tables. 

 

2.4 Carbon Emissions

Key Points

• Based on modelled energy use required to meet the SAP standard heating regime [5], the average Scottish home was estimated to produce 6.5 tonnes of carbon dioxide (CO2) per year in 2021, which is approximately double the average carbon emissions per household as reported by Department for Energy Security and Net Zero (3.3 tonnes per year) in 2020, 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 was 69 kg per square meter of floor area in 2021.

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 the Methodology 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 7.3). 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].

Table 2.11 shows that 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 2.3). Post-1982 tenement and other flats have the lowest modelled emissions on average (3.3 and 3.4 tonnes per year, respectively).

Table 2.11: Modelled Annual Carbon Emissions by Dwelling Age and Type, 2021

Dwelling Age	Dwelling Type	Carbon Emissions (tonnes/ year)	Carbon Emissions (kg/sqm)
Pre-1919	Detached	16.9	108
Pre-1919	Semi-detached	11.0	83
Pre-1919	Terraced	9.7	87
Pre-1919	Tenement	4.3	78
Pre-1919	Other flats	8.9	91
Pre-1919	All dwelling types	8.9	87
1919-1982	Detached	9.9	73
1919-1982	Semi-detached	6.4	71
1919-1982	Terraced	6.0	70
1919-1982	Tenement	4.1	68
1919-1982	Other flats	4.4	66
1919-1982	All dwelling types	6.2	70
Post-1982	Detached	7.8	55
Post-1982	Semi-detached	5.1	58
Post-1982	Terraced	4.4	57
Post-1982	Tenement	3.3	54
Post-1982	Other flats	3.4	56
Post-1982	All dwelling types	5.5	56
All Dwelling ages	Detached	10.1	71
All Dwelling ages	Semi-detached	6.6	70
All Dwelling ages	Terraced	6.3	70
All Dwelling ages	Tenement	3.9	67
All Dwelling ages	Other flats	5.0	68
All Dwelling ages	All dwelling types	6.5	69

Sample sizes are available on Table EE14 in 'Energy Efficiency' tables.

Across all age bands, detached houses have the highest modelled emissions due to a larger share of exposed surfaces (between 7.8 tonnes per year for post-1982 dwellings to 16.9 tonnes per year for pre-1919 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 and coal in place of mains gas.

Dwellings with larger floor areas generally have higher carbon emissions (see Table EE14 in 'Energy Efficiency' tables.).

By dividing modelled emissions by total internal floor area we derive carbon dioxide (CO2) emissions per square meter (kg/m2). Controlling for floor area in this way (see Table 2.11) shows that pre-1919 detached (108 kg/m²) houses have the highest modelled emissions per square meter. Post-1982 dwellings have the lowest emissions, particularly detached dwellings (55 kg/m2), and tenements (54 kg/m2).

2.4.2 Modelled Emissions by Tenure

Table 2.12 show how emissions differ across tenure in 2021. The highest emissions were observed for private rented dwellings (78 kg/m2) and lowest for housing association dwellings (63 kg/m2), with emissions from the other tenures falling in between those values.

Table 2.12 : Average Modelled Emissions by Tenure, 2021

Tenure	Average Modelled Emissions (kg per square meter)	Sample Size (number)
Owner occupied	70	1.,338
Mortgaged	67	762
LA	68	375
HA	63	276
Private rented	78	423
All Tenures	69	3,174

 

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 2021 have been described in this report based on SAP 2012 under RdSAP v9.93. 

As shown in Table 2.13, 38% of dwellings had EIRs in band C or above. The mean rating was 63 and the median was 65, both of which fall in band D. 6% of dwellings had EIRs in band F or G.

Table 2.13: EIR Bands in the Scottish Housing Stock, 2021 SAP 2012 (RdSAP v9.93)

EIR Band	Percentage of dwellings (%)	Number of dwellings (thousands)
A - B (81+)	7%	170
C (69-80)	31%	786
D (55-68)	39%	984
E (39-54)	17%	430
F (21-38)	5%	134
G (1-20)	1%	26
All EIR Bands	100%	2,529
Mean	63
Median	65
Sample size (number)	3,174

Table 2.14 shows how EIRs vary across different type of dwellings. As expected dwellings built post-1982 have (higher) better EIRs than other dwellings, with 67% rated band C or better and only 1% in the bottom two bands (F and G). 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.

Table 2.14: SAP 2012 (RdSAP v9.93): Mean EIR and Broad EIR Band, by Dwelling Characteristics, 2021 [note 2] [note 3]

Dwelling Characteristics	Category	Environmental Impact Rating (Mean)	EIR Band ABC (%)	EIR Band DE (%)	EIR Band FG (%)
Dwelling Type	Detached	57.3	26%	60%	14%
Dwelling Type	Semi-detached	60.8	24%	71%	5%
Dwelling Type	Terraced	61.6	29%	66%	5%
Dwelling Type	Tenement	68.9	61%	36%	3%
Dwelling Type	Other flats	65.9	52%	45%	4%
Dwelling Type (grouped)	House	59.8	26%	65%	8%
Dwelling Type (grouped)	Flat	67.9	58%	39%	3%
Dwelling Age	pre-1919	53.6	23%	59%	18%
Dwelling Age	1919-1944	60.6	26%	69%	5%
Dwelling Age	1945-1964	62	27%	70%	3%
Dwelling Age	1965-1982	62.4	32%	63%	6%
Dwelling Age	post-1982	70.9	67%	32%	1%
Primary Heating Fuel	Gas	65.9	43%	56%	1%
Primary Heating Fuel	Oil	42.1	2%	58%	40%
Primary Heating Fuel	Electric	49.9	15%	62%	23%
Primary Heating Fuel	Other fuel type	61.3	61%	17%	22%
Urban-Rural Indicator	Urban	64.8	41%	56%	3%
Urban-Rural Indicator	Rural	52.1	20%	58%	22%
Gas Grid	On grid	64.2	38%	59%	3%
Gas Grid	Off grid	55.2	35%	42%	24%
All dwellings	All dwellings	62.7	38%	56%	6%

Sample sizes are available on Table EE19 in 'Energy Efficiency' tables.

 

Footnotes

[5] The standard heating regime is: 21°C in the living room (zone 1) and 18°C in other rooms (zone 2) for 9 hours a day during the week and 16 hours a day during the weekend.