Energy Efficiency Standard for Social Housing: peer review

Case Study Group E

12. 1976-1983 mid floor flat, 60m ²
13. 1976-1983 mid-terrace house, 84m ²
14. 1976-1983 semi-detached house, 108m ²

Case Study Group E: 1990 Baseline

Walls

• 1093 tenement dwellings were identified by the 1991 SHCS as belonging to the social housing sector and constructed between 1965 and 1990:
  • 95% of these featured cavity wall construction.
  • Almost half (47%) were noted to feature insulation to all external walls.
• 1210 mid-terrace, end-terrace and semi-detached dwellings were identified by the 1991 SHCS as belonging to the social housing sector and constructed between 1965 and 1990:
  • 578 of these were mid-terrace dwellings, of which 91% featured cavity wall construction.
  • 632 of these were end-terrace or semi-detached dwellings, of which 93% featured cavity wall construction.
  • 43% of the 1210 dwellings were noted to feature insulation to all external walls.
• This SHCS age group spans 25 years, therefore where case study group 'E' describes the earlier half of this period of construction, the 1990 baseline assumption of 'no wall insulation' is considered acceptable.
• The RdSAP methodology assumes a wall U-value of 1.0 W/m ².K for age band F 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 and1991 ( RdSAP age bands C to G).
• Based on the calculation detailed in section S5.4 of Appendix S, the U-value calculated for case studies 13 and 14 are 0.67 W/m ².K and 0.62 W/m ².K respectively.

Roof

• The majority of 1965 to 1990 social rented houses (mid-terrace, end-terrace and semi-detached only), surveyed for the 1991 SHCS, featured a satisfactorily level of loft insulation (85%), 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.

Glazing

• The 1991 SHCS identified 1093 social rented tenements constructed between 1965 and 1990, of which 63% featured single glazing, although 31% were noted to feature full double glazing.
• The majority of the 1210 social rented houses (mid-terrace, end-terrace and semi-detached only) constructed between 1965 and 1990, surveyed by the 1991 SHCS, featured single glazing (66%), although 26% were noted to feature full double glazing.
• For this SHCS age group, the improved specification may be more predominant in construction occurring after 1983, therefore single glazing seems an appropriate 1990 baseline assumption for case study group E.

Ventilation: Chimneys

• The 1991 SHCS indicates that only 11% of social rented tenements, and 30% of social rented houses (mid-terrace, end-terrace and semi-detached only), constructed between 1965 and 1990, featured a gas or solid fuel fire. The 1990 baseline assumption of 'no open chimneys' is therefore considered appropriate.

Space and water heating

• Case study group E specifies factory applied foam insulation thickness of 25mm for the hot water cylinder. This is better than the default performance specification (12mm loose jacket) assumed by RdSAP for hot water cylinders in post-1965 constructed 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:
  • 78% of electric heated, social rented tenement dwellings, constructed between 1965 and 1991, featured storage heaters and 90% used electric immersion to provide hot water.
  • 74% of electric heated, social rented mid-terrace, end-terrace and semi-detached houses, constructed between 1965 and 1991, featured storage heaters and 88% used electric immersion to provide hot water.
• The 1990 baseline assumptions reflect these observations.

Gas heated dwellings
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%.

Recommendations:

• Reference should be made to Appendix E of the main report in relation to the 1990 baseline assumption for loft insulation.
• 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 E: SHQS 2015

• The case studies feature 25mm of factory applied foam insulation to the hot water tank. As long as the pipes are insulated, or contribute to the space heating requirement, both 12E and 12G comply 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 boiler specified for the baseline property meet the necessary criteria
• The 1990 baseline forms of case study 12 (both electric and gas heated) meet the minimum SAP criteria required for element 35 of Annex C, therefore only cavity wall insulation is required to comply with the other elements.

Walls

• Based on element 31 of Annex C for the SHQS, cavity wall insulation must be installed for all the dwellings.
• The RdSAP assumptions specify a U-value of 0.40 W/m ².K for a filled cavity wall constructed in Scotland between 1976 and 1983.

Roof

• Element 32 of Annex C is not applicable to case study 12, where it cannot accommodate loft insulation.
• A loft insulation thickness of at least 100mm is necessary for case studies 13 and 14 to meet compliance with element 32 of Annex C for the SHQS.

Electric heated dwellings
Roof

• It is necessary to increase the loft insulation thickness to 250mm for case study 14E, to exceed the minimum SAP rating, in line with element 35 of Annex C.

Glazing

• Case study 13E is reliant on the installation of double glazing to help exceed 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 considered.
• The selection of post-2003 glazing over pre-2003 glazing, for case study 14E, emphasises the challenge this dwelling faces to comply with element 35 of Annex C, where it just exceeds the minimum SAP rating by two points

Space and water heating

• Free-standing large volume electric storage systems may be deemed efficient as long as they were installed after 1984, however it may be necessary to upgrade to an improved system to help exceed the minimum SAP rating for element 35 of Annex C.
• The fan storage heaters, proposed for case studies 13E and 14E, will have the same efficiency as the previous system, but will benefit from increased 'responsiveness' ^[14] and automatic controls. This will contribute to reduced space heating requirements, fuel costs and consequently a better SAP rating.

Gas Heated dwellings
Glazing

• Case study 14G is reliant on the installation of double glazing to help exceed 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 considered.

Recommendations:

• There are no recommended changes to the assumptions specified for the ' SHQS 2015' improvement stage for case study 12.

Case Study Group E: Further measures 2020

• The EESSH outlines a minimum EI rating to be achieved for electric fuelled properties and gas fuelled properties. These are:
  • a C (70) and C (80) respectively for a mid-floor flat,
  • a D (55) and C (70) respectively for a mid-terrace house, and
  • an E (50) and D (65) respectively for an end-terrace or semi-detached house.
• No additional measures are suggested under this stage for case study 14E, where the work undertaken to meet compliance with the ' SHQS 2015' mean it has also exceeded the minimum EI rating for the EESSH.
• Additional measures are proposed for case study 13E, however it just falls short of the minimum EI rating (by 1 point) therefore does not meet compliance with the EESSH until application of the 'advanced measures 2050'.

Roof

• Where feasible (and if not undertaken as a prior measure), the loft insulation thickness is increased to 250mm for the electric and gas heated dwellings ( i.e. case studies 13E, 13G and 14G).

Electric Heating
Glazing

• Case study 12E specifies the replacement of its single glazing with post-2003 double glazing to help exceed the minimum EI rating.
• RdSAP assumes a U-value of 3.1 W/m ².K and 2.0 W/m ².K for pre-2003 and post-2003 double glazing specifications respectively, however the latter is a more appropriate specification for future improvements, and consequently any suggested under the 'further measures 2020' stage.
• This may not be a suitable measure for similar dwelling types, should the glazing have previously been upgraded to 'pre-2003' double glazing standards.

Space and water heating

• The proposed fan storage heater will have the same efficiency as the older storage systems, but will benefit from increased 'responsiveness' ^[15] and automatic controls, contributing to reduced space heating requirements, and consequently an improved EI rating.
• The improvement to the hot water tank insulation, increasing the factory applied foam insulation thickness 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 heated dwellings
Glazing

• Case studies 12G and 13G specify the replacement of single glazing with post-2003 double glazing to help exceed the minimum EI rating.
• RdSAP assumes a U-value of 3.1 W/m ².K and 2.0 W/m ².K for pre-2003 and post-2003 double glazing specifications respectively, however the latter is a more appropriate specification for future improvements, and consequently any suggested under the 'further measures 2020' stage.
• This may not be a suitable measure for similar dwelling types, should the glazing have previously been upgraded to 'pre-2003' double glazing standards.

Space and water heating

• The indicative life expectancy for a condensing boiler is in the region of 15 years ^[16] , 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.
• 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.

Recommendations:

• Case study 13E should consider additional measures (such as increasing the hot water system insulation thickness) to ensure it meets compliance with the EESSH minimum EI rating.
• 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 E: Advanced measures 2050

• No additional measures are considered for case study 12 (electric or gas heated) under the 'advanced measures 2050' stage.

Floor

• 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 the installation of a central heating system, may provide an opportunity to install the floor insulation with minimal additional disruption.
• The installation of 50mm of floor insulation improves the U-value of a solid ground floor from 0.67 W/m ².k to 0.33 W/m ².K for case study 13, and from 0.62 W/m ².k to 0.32 W/m ².K for case study 14.

Renewables: Solar PVs to 20% of roof

• Photovoltaic technology, specified for case studies 13 and 14, will only be suitable for a limited number of properties, where they meet sufficient criteria to ensure the effective operation of the technology ( e.g. suitable orientation, sufficient space on the roof, optimal angle of roof, minimal over shading).
• Should optimal conditions associated with any of the above criteria not be met, additional costs may be incurred to try optimise operational conditions ( e.g. investment in a supporting frame to improve the tilt angle, or multiple inverters to minimise the impact of partial shading for periods of the day).

Electric heated dwellings
Glazing

• Post 2003 double glazing is included as an 'Advanced Measure 2050' for case study 13E, where it is unlikely be implemented in the near future subject to 'pre-2003' glazing being one of the previous improvement efforts for the electric heated dwelling.

Space and water heating

• The improvement to the hot water tank insulation for case study 13E, increasing the factory applied foam insulation thickness from 25mm to 80mm, identifies another method by which landlords can reduce the hot water energy consumption, CO ₂ emissions and consequently EI rating.
• Had this been specified as an ' SHQS 2015' or 'further measures 2020' improvement, case study 13E may have been able to meet compliance with the EESSH criteria earlier in the process.

Gas Heating
Glazing

• Post 2003 double glazing is included as an 'Advanced Measure 2050' for case study 14G, where it is unlikely be implemented in the near future subject to 'pre-2003' glazing being one of the previous improvement efforts for the gas heated dwelling.

Recommendations:

• Specification of 80mm factory applied foam for the electric immersion hot water system may be better suited under a previous improvement stage, to help the dwelling meet the necessary criteria for the EESSH.