Publication - Research and analysis

Energy Efficiency Standard for Social Housing: peer review

Published: 22 Oct 2013
Energy and Climate Change Directorate
Part of:
Environment and climate change

Peer review scrutinising the example dwellings in the Energy Efficiency Standard for Social Housing consultation document.

Energy Efficiency Standard for Social Housing: peer review
Case Study Group C

Case Study Group C

7. 1919-1949 Four in a block, Lower, 94m 2
8. 1919-1949 Four in a block, Upper, 87m 2

Case Study Group C: 1990 Baseline


  • 742 four in a block dwellings were identified by the 1991 SHCS as belonging to the social housing sector, and constructed between 1919 and 1944. Of these, 90% featured cavity wall construction.
  • The 1990 baseline assumption of 'no insulation' is in line with the majority of these dwellings, where only 24% of the 742 dwellings were noted to have some form of insulation to all external walls.
  • The RdSAP methodology v9.91 assumes a wall U-value of 1.6 W/m 2.K for age bands B & C cavity walls (as built) in Scotland (v9.90 and v9.91).

Ground Floor

  • Where it is not possible to determine the level of floor insulation, the RdSAP methodology assumes a solid floor with no insulation for Scottish dwellings constructed between 1930 and 1991 ( RdSAP age bands C to G).
  • Based on the calculation detailed in section S5.4 of Appendix S, a U-value of 0.53 W/m 2.K is determined for case study 7.


  • Observations from the 1991 SHCS indicate that the majority (77%) of social rented, four in a block dwellings, constructed between 1919-1944 and able to accommodate loft insulation, featured a satisfactorily level (defined then as 100mm). This has required further investigation to determine the validity of the baseline assumption, as discussed in Appendix E of the main report.


  • The majority (74%) of the 742 social rented, four in a block dwellings (identified by the 1991 SHCS) featured single glazing, although a quarter were observed to have fully upgraded to double glazing.

Ventilation: Chimneys

  • The 1991 SHCS indicates that 87% of social rented, four in a block dwellings, constructed between 1919 and 1944, featured a gas or solid fuel fire.
  • These would require some form of open chimney to remove combustion products. The RdSAP calculation should include a count of chimney or flues (unless it meets any of the criteria specified in section 'S4 Parameters for ventilation rate' of Appendix S). Exclusion of this will contribute to an underestimation of the infiltration associated with the property and consequently a reduced space heating requirement.

Space and water heating

  • The 1991 SHCS indicates that just over a fifth (22%) of the social rented, four in a block dwellings, constructed between 1919 and 1944, do not feature any central heating and 24% had only partial central heating. Despite this, the RdSAP calculation operates under the assumption that the entire dwelling is heated. It should be remembered that the calculated values are not representative of actual energy consumption and CO 2 emissions.
  • Case studies 7E and 7G specify 25mm of factory applied foam insulation for the hot water cylinder. This is better than the default performance specification (12mm loose jacket) assumed by RdSAP for hot water cylinders in 1919-1944 Scottish dwellings. It is not until after 1984 that 25mm factory applied foam insulation is the default RdSAP assumption

Electric heated dwellings
Space and water heating

  • Based on observations from the 1991 SHCS, 91% of electric heated, social rented four in a block dwellings, constructed between 1919 and 1944, featured storage heaters, and 84% were provided with hot water via electric immersion.
  • The 1990 baseline assumptions reflect these observations.

Gas heating and hot water
Space and water heating

  • It is unlikely that data will be available describing the efficiency of the boiler installed in the 1990 property, therefore it will be necessary to refer to the assumptions detailed within the SAP methodology: Appendix S assumes pre 1998 gas boilers are not fan-assisted, which corresponds to an efficiency of 66% (with the exception of a regular floor mounted boiler installed pre 1979 with an assumed efficiency of 56%).
  • Should any of the efficiency adjustments outlined in Table 4c of the SAP methodology be applicable, the boiler efficiency may be reduced by 5%. This means a regular, non-condensing, pre-1998 gas boiler (not fan assisted) without any thermostatic control of room temperature will be assumed to have an overall efficiency of 61%.


  • The remaining number of open chimneys and/or flues should be considered for dwellings constructed between 1919 and 1949.
  • The minimum efficiency assumed for the boiler winter seasonal efficiency (applied for the space heating requirement) should be no less than 61%.

Case Study Group C: SHQS 2015

  • The case studies feature 25mm of factory applied foam insulation on the hot water tank. As long as the pipes are insulated, or contribute to the space heating requirement, case study group C complies with element 33 of Annex C.
  • Sub-elements 34A and 34B require that the property features a full central heating system addressing all habitable rooms (excluding the kitchen and bathroom), and that it is deemed efficient. Both the storage heaters and gas boilers specified for the baseline property meet the necessary criteria.


  • Based on element 31 of Annex C, for the SHQS, cavity wall insulation must be installed.
  • The RdSAP assumptions specify a U-value of 0.50 W/m 2.K for a filled cavity wall constructed in Scotland between 1919 and1949. This performance specification is better than the default assumptions associated with v9.90 insulated timber frame constructions (0.55 W/m 2.K) or system build (0.60 W/m 2.K) therefore such construction types are likely to experience greater challenges to realising the necessary SHQS SAP rating.


  • Loft insulation of at least 100mm thickness is necessary to meet compliance with element 32 of Annex C for the SHQS.
  • This is only applicable to case study 8 (where it cannot be accommodated by case study 7).

Electric heated dwellings

  • To exceed the minimum SAP rating, it is necessary to increase the loft insulation thickness from the minimum 100mm, to 250mm for case study 8E.


  • The selection of post-2003 glazing over pre-2003 glazing emphasises the challenge faced by case study 7E to comply with element 35 of Annex C. This means this measure, in association with the other proposed improvements, helps the dwelling exceed the minimum SAP rating by just four points.
  • Case study 8E is reliant on the installation of double glazing to help achieve the minimum SAP rating. Specification of pre-2003 glazing allows landlords to view the potential benefits associated with this measure, whilst providing flexibility to choose better glazing specifications to realise the SAP rating should they not be able to accommodate any of the other energy efficiency measures outlined.

Space and water heating

  • The fan storage heaters, specified for case study 7E, will have the same efficiency as the older storage systems, but will benefit from increased 'responsiveness' [8] and automatic controls. This will contribute to a reduction in the space heating requirement, and consequently an improved SAP rating.
  • The increased hot water tank insulation, specified for case study 7E, identifies another method by which landlords can reduce the hot water energy consumption, CO 2 emissions and consequently SAP rating.

Gas heated dwellings

  • Case study 8G meets compliance with element 32 by specifying the minimum 100mm of loft insulation.


  • There are no recommended changes to the assumptions specified for the ' SHQS 2015' improvement stage, for case study group C.

Case Study Group C: Further measures 2020

  • The EESSH outlines a minimum EI rating to be achieved for electric fuelled properties and gas fuelled properties, which are:
    • E (50) and D (60) respectively for a lower four in a block dwelling, and
    • D (55) and D (60) respectively for an upper four in a block dwelling.
  • The additional energy efficiency measures necessary to qualify for the SHQS 2015 SAP rating mean electric heated case studies 7E and 8E already meet the required rating. Case study 8E still goes on to consider the effect of upgrading the heating system under the 'further measures 2020' stage of improvements.
  • Gas heated case studies 7G and 8G require further measures to exceed the aforementioned EI rating.

Electric space and water heating
Space and water heating

  • The fan storage heaters considered for case study 8E will have the same efficiency as the older storage systems, but will benefit from increased 'responsiveness' [9] and automatic controls. This will contribute to a reduction in the space heating requirement, and consequently an improved EI rating.
  • The improved hot water tank insulation specified for case study 8E (increasing the factory applied foam insulation from 25mm to 80mm) identifies another method by which landlords can reduce the hot water energy consumption, CO 2 emissions and consequently EI rating.

Gas heating and hot-water

  • - In order to exceed the proposed EI rating in line with the EESSH, the loft insulation thickness for case study 8G has been increased to 250mm in addition to upgrading the heating system. The combined effect of these measures takes the EI rating well above the minimum value, by as much as 16 points.

Space and water heating

  • The indicative life expectancy for a condensing boiler is in the region of 15 years [10] , therefore installation of a new system is appropriate for both the ' SHQS 2015' or 'Further Measures 2020' improvement stages. This also provides an opportunity to upgrade the control strategy.
  • Table 4b of the SAP methodology specifies a non-condensing combi-boiler to have an efficiency of 70-74%. Any installations after 2005 will be condensing systems, thus assume an efficiency of 80-84%. The case study control specification indicates that the system does not qualify for any efficiency adjustments detailed in table 4c of the SAP methodology.
  • An improved boiler efficiency will yield considerable space heating and hot water energy reductions. Standard 6.3 of the Domestic Technical Handbook specifies a minimum seasonal efficiency of 88% ( SEDBUK 2009) for gas boilers. It is proposed that this value is used to describe the efficiency for any future installations, where it represents the current minimum standards.
  • A more efficient boiler will use less energy to address the load on the heating system. Any savings realised by a measure which reduces the load on the heating system will be greater under the operation of a less efficient boiler compared to a more efficient system. This is important to bear in mind when considering the cumulative effect of implementing energy efficiency measures installed over a number of stages: the benefits of individual measures cannot be added together.


  • An assumed gas boiler efficiency of 88% is proposed in line with the minimum standards outlined by Standard 6.3 of the Domestic Technical Handbook.
  • Social landlords should be reminded that the case studies demonstrate the cumulative application of efficiency measures over three stages, and the potential benefits realised by a single measure are subject to change in relation to the other measures in place.

Case Study Group C: Advanced measures 2050


  • The installation of floor insulation is a particularly disruptive process, and would likely incur additional expense for the duration of the work, where occupants may need to be provided with alternative accommodation and their possessions put into storage. Despite this, the installation of other improvement measures which require the floorboards to be raised (such as installation of a central heating system) may provide an opportunity to install the floor insulation with minimal additional disruption.
  • The default performance parameters associated with the floor construction are one of the only factors which differentiate dwellings from RdSAP age band B and RdSAP age band C. The former construction period assumes suspended timber floors, and the latter solid floors.
  • The installation of 50mm of floor insulation improves the U-value of a solid ground floor (applicable to case study 7 only) from 0.52 W/m 2.k to 0.28 W/m 2.K.
  • The calculation provided by the RdSAP methodology to determine the U-value for suspended timber floors does not appear to accommodate the benefit of insulation. Social landlord may wish to provide documentary evidence of the improved floor U-value, should they wish to override the default assumption applied for the RdSAP calculation.

Gas space and water heating

  • Post 2003 double glazing is included as an 'Advanced Measure 2050', where it is unlikely that this measure will be implemented in the near future subject to 'pre-2003' glazing being one of the previous improvement efforts.


  • Social landlords should be advised to acquire documented evidence detailing the improved U-value associated with an insulated suspended timber floor, should they wish to override the default RdSAP assumption.


Email: Agnes Meany