Energy Efficiency Standard for Social Housing: peer review

Case Study Group B

4. Interwar cavity wall mid floor flat, 78m ²
5. Interwar cavity wall mid terrace house, 80m ²
6. Interwar cavity wall semi-detached house, 92m ²

Case Study Group B: 1990 Baseline

Walls

• 492 social rented tenement dwellings, identified by the 1991 SHCS, were constructed between 1919 and 1944:
  • Only 15% featured any form of wall insulation to all external walls.
• 363 mid-terrace, end-terrace and semi-detached dwellings were identified by the 1991 SHCS as belonging to the social housing sector and constructed between 1919 and 1944:
  • Of the 92 mid-terrace dwellings, only 39% were noted to have some form of insulation to all external walls.
  • Of the 271 semi-detached or end-terrace dwellings, only 34% were noted to have some form of insulation to all external walls.
• Based on the above, 'no insulation' is considered an appropriate assumption for the 1990 baseline case studies.
• The RdSAP methodology assumes the same performance parameters for age bands B (1919-1929) and C (1930-1949) with respect to wall thickness and U-values. For a cavity wall (as built) in Scotland, this is a thickness of 300mm and U-value of 1.6 W/m ².K (v9.90 and v9.91).

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-value calculated for case studies 5 and 6 is in the region of 0.52 W/m ².K and 0.64 W/m ².K respectively.

Roof

• The majority of 1919-1944 social rented houses (mid-terrace, end-terrace and semi-detached only), surveyed for the 1991 SHCS, featured a satisfactorily level of loft insulation (81%), 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 properties surveyed for the 1991 SHCS indicate that:
  • the majority of social rented tenements, constructed between 1919 and 1944, featured single glazing (70%), as per the baseline assumption. 27% were noted to have fully upgraded to double glazing.
  • the majority of social rented, houses constructed between 1919 and 1949 featured single glazing (71%), as per the baseline assumption. 26% were noted to have fully upgraded to double glazing.

Ventilation: Chimneys

• Over three quarters (78%) of the social rented tenements, constructed between 1919 and 1944 and surveyed for the 1991 SHCS, featured a gas or solid fuel fire.
• The 1991 SHCS indicates that 87% of social rented houses (mid-terrace, end-terrace and semi-detached only) constructed between 1919 and 1944, featured a gas or solid fuel fire.
• These dwellings would likely require some form of open chimney to remove combustion products and this should be accounted for within the RdSAP calculation (unless any of the exceptions detailed in section 'S4 Parameters for ventilation rate' of Appendix S apply). Exclusion of this will contribute to an underestimation of the infiltration associated with the dwellings, and consequently a reduced space heating requirement.

Space and water heating

• 60% of social rented tenements and 40% of the social rented houses (mid-terrace, end-terrace and semi-detached only), constructed between 1919 and 1944 and surveyed for the 1991 SHCS, only had partial or no central heating. Despite this, the RdSAP methodology operates on the basis 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 B specifies a 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 Scottish dwellings constructed between 1919 and 1949. It is not until 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,
  • 82% of electric heated, social rented tenement dwellings constructed between 1919 and 1944, featured storage heaters and 92% used electric immersion to provide hot water.
  • 98% of electric heated, social rented houses, constructed between 1919 and 1944, featured storage heaters, and 76% were provided with hot water via electric immersion
• The 1990 baseline assumptions are in line with 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:

• Social landlords should be advised to obtain documentary evidence of the improved U-value for insulated suspended timber flooring, if they wish to override the default assumption used in RdSAP.
• Reference should be made to Appendix E of the main report regarding the loft insulation assumptions for the 1990 baseline dwelling.
• A count of the chimneys and/or flues should be included for dwellings constructed between 1919 and 1949.
• The minimum efficiency assumed for the boiler winter seasonal efficiency (applied for the space heating requirement) should not be less than 61%.

Case Study Group B: 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, case study group B 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 1990 baselines meet the necessary criteria.
• The 1990 baseline version of the gas heated case study 4G exceeds the minimum SAP rating to meet compliance with Element 35 of Annex C, however improvement measures are required to meet compliance with the other elements of Annex C.

Walls

• Based on element 31 of Annex C for the SHQS cavity wall insulation must be installed for all the dwellings in case study group B.
• The RdSAP assumptions specify a U-value of 0.50 W/m ².K for a filled cavity wall constructed in Scotland between 1919 and 1949. This performance specification is better than the default assumptions associated with insulated timber frame constructions (0.55 W/m ².K) or system build (0.60 W/m ².K) therefore these latter construction types are likely to experience greater challenges to realising the necessary SHQS SAP rating.

Roof

• Loft insulation of at least 100mm thickness is necessary to meet compliance with element 32 of Annex C for the SHQS (this is not applicable to case study 4 which cannot accommodate loft insulation).

Electric heated dwellings
Roof

• Electric heated case studies 5E and 6E must increase the loft insulation thickness to 250mm, to exceed the minimum SAP rating, in line with element 35 of Annex C.

Glazing

• Case study 4E specifies the installation of pre-2003 double glazing. This measure, in addition to the wall insulation, helps achieve a SAP rating of 69, which is 11 points above the minimum criteria for element 35 of Annex C.
• Case study 5E also specifies the installation of pre-2003 double glazing, whereas the specification of post-2003 glazing for case study 6E emphasises the challenge this dwelling faces in trying to meet compliance with element 35 of Annex C.

Space and water heating

• The fan storage heaters specified for case studies 5E and 6E will have the same efficiency as the previous system, but will benefit from increased 'responsiveness' ^[5] and automatic controls. This will contribute to reduced space heating requirements, fuel costs and consequently a better SAP rating.
• The improvement to the hot water tank insulation for case studies 5E and 6E, increasing the factory applied foam insulation thickness from 25mm to 80mm, identifies additional efforts landlords can implement to help realise the necessary SAP rating for element 35

Gas heated dwellings
Roof

• Gas heated case studies 5G and 6G meet compliance with the SHQS 2015 criteria by specifying the minimum loft insulation thickness of 100mm.

Glazing

• In addition to the cavity wall and loft insulation, case study 6G specifies pre-2003 glazing as an improvement measure under the ' SHQS 2015' stage. The combined installation of these measures takes the SAP rating well above the minimum requirement.

Recommendations:

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

Case Study Group B: 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 4E just meets the minimum EI rating subject to the previous improvements undertaken for the ' SHQS 2015' stage, but further improvements are still considered.
• Electric heated case studies 5E and 6E do not consider any further improvements for this stage, where they have already met the EESSH criteria subject to the SHQS 2015 improvement measures.
• Gas heated case studies 4G, 5G and 6G require further measures to exceed the aforementioned EI ratings.

Electric heated dwellings
Space and water heating

• The fan storage heater specified for case study 4E will have the same efficiency as the older storage system, but will benefit from increased 'responsiveness' ^[6] and automatic controls. This will contribute to reduced space heating requirements, and consequently an improved EI rating.
• The improvement to the hot water tank insulation for case study 4E, 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
Roof

• It has been necessary to increase the loft insulation thickness to 250mm for case studies 5G and 6G (in addition to upgrading the heating system) to exceed the proposed EI rating in line with the EESSH.

Glazing

• The specification of post-2003 glazing for case study 4G (in addition to an upgraded heating system) assists in exceeding the target EI rating by 5 points.

Space and water heating

• The indicative life expectancy for a condensing boiler is in the region of 15 years ^[7] , 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.

Recommendations:

• 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 B: Advanced measures 2050

Floor

• The installation of floor insulation (applicable to case studies 5 and 6) is a particularly disruptive process. It 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, where the former assumes suspended timber and the latter solid floors.
• The installation of 50mm of floor insulation improves the U-value of a solid ground floor from 0.52 W/m ².k to 0.28 W/m ².K (for case study 5) and 0.64 W/m ².k to 0.32 W/m ².K (for case study 6).
• 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 landlords 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.

Renewables: Solar PVs to 20% of roof

• Photovoltaic technology (specified for case studies 5 and 6) 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 optimise operational conditions ( e.g. investment in a supporting frame to improve the tilt angle, or multiple inverters to minimise the impact of shading for periods of the day).

Electric heated dwellings
Glazing

• Considered independent of other measures, the RdSAP calculation indicates a further 5% reduction in CO ₂ emissions associated with the specification of post-2003 glazing (replacing pre-2003 glazing), for electric heated case study 4E.

Gas Heating
Glazing

• Post-2003 double glazing is included as an 'Advanced Measure 2050' for gas heated case studies 5G and 6G. It is unlikely that this measure will be implemented in the near future subject to the prior installation 'pre-2003' glazing.

Recommendations:

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