Energy Efficiency Standard for Social Housing: peer review

Case Study Group D

9. 1950-1964 mid floor flat, 110m ²
10. 1950-1964 mid-terrace house, 70m ²
11. 1950-1964 semi-detached house, 84m ²

Case Study Group D: 1990 Baseline

Walls

• 957 tenement dwellings were identified by the 1991 SHCS as belonging to the social housing sector and constructed between 1945 and 1964.
  • 89% featured cavity wall construction.
  • 22% were noted to have some form of insulation to all external walls.
• 1395 mid-terrace, end-terrace and semi-detached dwellings were identified by the 1991 SHCS as belonging to the social housing sector and constructed between 1945 and 1964.
  • 504 of these were mid-terrace dwellings, of which 92% featured cavity wall construction.
  • 891 of these were end-terrace or semi-detached dwellings, of which 89% featured cavity wall construction.
  • 41% of the mid-terrace dwellings were noted to have some form of insulation to all external walls.
  • an increasing proportion of end-terrace and semi-detached houses (45%) were noted to have some form of insulation to all external walls.
• The 1990 baseline assumption of 'no insulation' is in line with the greater proportion of these dwellings.
• The RdSAP methodology v9.91 assumes a wall U-value of 1.6 W/m ².K for age band D 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, the U-values calculated for case studies 10 and 11 are 0.48 W/m ².K and 0.74 W/m ².K respectively.

Roof

• The 1991 SHCS survey indicates that 84% of social rented houses constructed between 1945 and 1964 (mid-terrace, end-terraced and semi-detached only) featured a satisfactory level of loft insulation, 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 majority of the 957 social rented tenement dwellings constructed between 1945 and 1964 (and surveyed for the 1991 SHCS) featured single glazing (82%). 15% were noted to have fully upgraded to double glazing.
• The majority of the 1395 social rented mid-terrace, end-terrace and semi-detached houses constructed between 1945 and 1964 (and surveyed for the 1991 SHCS), featured single glazing (74%), although 21% were noted to have fully upgraded to double glazing.

Ventilation: Chimneys

• The 1991 SHCS indicates that:
  • just over half (55%) of social rented, tenement dwellings constructed between 1945 and 1964, featured a gas or solid fuel fire.
  • 82% of social rented houses (mid-terrace, end-terrace and semi-detached only) constructed between 1945 and 1964, featured a gas or solid fuel fire.
• These properties would likely require some form of open chimney to remove combustion products. The RdSAP calculation should therefore include a count of chimney or flues (unless the dwellings meet 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 over half (55%) of the social rented tenements constructed 1945-1964 did not feature any central heating, and 17% had only partial central heating.
• Compared to the previous age groups and building types, a decreasing number of social rented houses (mid-terrace, end-terrace and semi-detached only) constructed between 1945 and 1964 and surveyed for the 1991 SHCS did not feature any central heating (38%).
• 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 study group D 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 1945-1964 constructed Scottish dwellings. It is not until after 1984 that 25mm factory applied foam insulation is the default RdSAP assumption.

Electric heated dwellings

• Based on observations from the 1991 SHCS:
  • 88% of electric heated, social rented tenement dwellings constructed between 1945 and 1964, featured storage heaters and 91% used electric immersion to provide hot water.
  • 92% of electric heated, social rented houses (mid-terrace, end-terrace and semi-detached only), constructed between 1945 and 1964, featured storage heaters and 82% used electric immersion to provide hot water
• The 1990 baseline assumptions for case study group D are in line with these observations.

Gas heated dwellings

• 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 which has an assumed efficiency of 56%).
• Should any of the efficiency adjustments outlined in Table 4c 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 regarding the 1990 baseline assumption for loft insulation.
• A count of the chimneys and/or flues should be included for dwellings constructed between 1945 and 1964.
• 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 D: SHQS 2015

• Case study group D features 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, the case studies will 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.
• Both the electric and gas heated versions of case study 9 exceed the minimum SAP rating in the 1990 baseline state. Cavity wall insulation is therefore the only measure necessary to meet all the requirements associated with Annex C of the SHQS.

Walls

• Based on element 31 of Annex C for the SHQS, cavity wall insulation must be installed for all the case study dwellings in group D.
• The RdSAP assumptions specify a U-value of 0.50 W/m ².K for a filled cavity wall constructed in Scotland between 1950 and1964. The default RdSAP assumption for insulated 'system build' wall construction demonstrates poorer thermal properties (0.6 W/m ².K), and as such will experience greater challenges to realising the necessary SHQS SAP rating.

Roof

• Element 32 of Annex C is not applicable to case study 9, where it cannot accommodate loft insulation.
• A minimum loft insulation thickness of 100mm is necessary for case studies 10 and 11, to meet compliance with element 32 of Annex C for the SHQS.

Electric Heating
Roof

• To exceed the minimum SAP rating (for element 35 of Annex C), it is necessary to increase the loft insulation thickness to 250mm for the electric heated case studies, 10E and 11E.

Glazing

• Case study 10E also requires the installation of pre-2003 double glazing to meet compliance with element 35 of Annex C.
• The selection of post-2003 glazing over pre-2003 glazing emphasises the challenge faced by case study 11E 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 is necessary for case studies 10E and 11E to upgrade to an improved system to help exceed the minimum SAP rating for element 35 of Annex C.
• The proposed fan storage heater will have the same efficiency, but will benefit from increased 'responsiveness' ^[11] and automatic controls. This will contribute to reduced space heating requirements, fuel costs and consequently a better SAP rating.
• The improved hot water tank insulation (from a thickness of 25mm to 80mm), identifies an additional effort by which landlords can help realise the necessary SAP rating for element 35.

Renewables: Solar PV to 10% of roof area

• Photovoltaic technology (specified for case study 11E) 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).
• Where solar PV is potentially limited in its suitability for some dwellings, it is suggested that the technology be reserved for consideration as part of the 'advanced measures 2050' stage.

Gas Heating
Roof

• A loft insulation thickness of only 100mm is needed for case studies 10G and 11G to meet compliance with element 32 of Annex C.

Recommendations:

• Alternative technologies should be considered to help case study 11E achieve the minimum SAP rating for the SHQS over solar PV, where the suitability of this technology is limited in relation to a number of building specific characteristics.

Case Study Group D: Further measures 2020

• The EESSH outlines a minimum EI rating to be achieved for electric and gas heated dwellings, which are:
  • C (70) and C (80) respectively for a mid- floor flat,
  • D (55) and C (70) respectively for a mid-terrace house, and
  • E (50) and D (65) respectively for an end-terrace/semi-detached house.
• Case study 10E has already met the necessary EI rating for EESSH, based on the measures installed during the ' SHQS 2015' improvement stage, and no additional measures are required.
• A number of additional measures are necessary to realise the aforementioned EI rating for case studies 9 and 11, as well as the gas heated case study 10G.
• Despite this, no additional measures are considered for case study 11E, therefore it just falls short of meeting the necessary EI rating (by 1 point) until application of the 'advanced measures 2050'.

Electric heated dwellings
Glazing

• One of the improvement measures proposed for case study 9E is the replacement of the single glazing with double glazing.
• 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.
• Post-2003 glazing may not be an appropriate specification for similar dwelling types, should social landlords have already installed double glazing prior to 2003.

Space and hot water heating

• The fan storage heaters, specified for case study 9E, will have the same efficiency as the older storage systems but benefit from increased 'responsiveness' ^[12] 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 (increased 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
Roof

• It has been necessary to increase the loft insulation thickness to 250mm (in addition to upgrading the heating system) to exceed the minimum EI rating for case studies 10G and 11G.

Space and water heating

• The indicative life expectancy for a condensing boiler is in the region of 15 years ^[13] , 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:

• Additional retrofit measures should be considered for case study 11E to ensure it meets compliance with the EESSH under the 'further measures 2020' stage.
• 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 D: Advanced measures 2050

Floor

• Floor insulation is proposed for electric and gas heated versions of case studies 10 and 11 (where it cannot be accommodated by case study 9).
• 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 0.48 W/m ².k to 0.27 W/m ².K for case study 10, and from 0.74 W/m ².k to 0.35 W/m ².K for case study 11.

Renewables: Solar PVs to 20% of roof

• Photovoltaic technology (considered only for case study 10E, 10G and 11E) 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). This means consideration of this technology is most suitable under the 'advanced measures 2050' stage, however this does not imply that social landlords cannot implement this technology sooner.
• 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 Heating
Glazing

• Post-2003 double glazing is included as an 'Advanced Measure 2050' for case study 10E, where (i) 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, and (ii) it is being considered as a future improvement.

Gas Heating
Glazing

• Post-2003 double glazing is included as an 'Advanced Measure 2050', where (i) none of the gas heated dwellings have yet upgraded from single glazing (as it has not been necessary to help meet the necessary SAP and EI ratings for the SHQS and EESSH), and (ii) it is being considered as a future improvement.
• The landlord can clearly identify the extent of the benefits this measure brings for case study 9G where it is the only 'advanced measure 2050' applied.

Recommendations:

• There are no recommended changes to the assumptions specified for the 'Advanced Measures 2050' improvement stage, for case study group D.