Energy Efficiency Standard for Social Housing: peer review

Case Study Group H

7. 1999-2007 mid floor flat, 73m ²
8. 1999-2007 mid terrace house, 97m ²
9. 1999-2007 semi-detached house, 73m ²

Case Study Group H: 1990 Baseline

Walls

• Compliance with the Building Standards (Scotland) Regulations 1990 (1999 Amendments) required U-values for exposed walls not to exceed 0.45 W/m ².K. This was upgraded in 2002 to a maximum U-value of 0.30 W/m ².K (0.27 W/m ².K for electrically heated dwellings).
• The RdSAP methodology v9.91 assumes a wall U-value of 0.45 W/m ².K and 0.30 W/m ².K for filled cavity walls (as built) in Scotland for age bands I and J respectively. This means it will be difficult for case study group H to be represented by a single RdSAP calculation where the period of construction traverses two different age bands.
• It is suggested the earlier RdSAP age band I is used (describing construction between 1999 and 2002) where this represents a greater challenge to improve the thermal performance.

Ground Floor

• Compliance with the Building Standards (Scotland) Regulations required floors to achieve a maximum U-value of 0.22 W/m ².K, or 0.45 W/m ².K depending on the amendment version of the regulations and a number of other factors.
• Where it is not possible to determine the level of floor insulation, the RdSAP methodology assumes a solid floor with 50mm or 75mm of insulation for Scottish dwellings constructed between 1999 and 2007 ( RdSAP age bands I and J respectively).
• Based on the calculation detailed in section S5.4 of Appendix S, the U-value calculated for case study 22 is in the region of 0.26 or 0.22 W/m ².K for age bands I and J respectively, and for case study 23, in the region of 0.33 or 0.26 W/m ².K.
• Where the default assumptions associated with RdSAP age band I are applied, the floor U-values are in compliance with the minimum building standards.

Roof

• Table S9 in appendix S states an assumed roof U-value of 0.20 W/m ².K for a slate or tile roof featuring 200mm insulation.
• If the loft insulation thickness is not known and table S10 from Appendix S applies, dwellings constructed in Scotland between 1999 and 2007 assume a default U-value of 0.26 W/m ².K or 0.16 W/m ².K, associated with an insulation thickness of 150mm and 250mm respectively, for a pitched, slate or tile roof with insulation between joists.
• Compliance with the Building Standards (Scotland) Regulations required pitched roofs with insulation between the joists to achieve a U-value between 0.16 and 0.25 W/m ².K, depending on the amendment version of the regulations and a number of other factors.
• This has required further investigation to determine the validity of the baseline assumption, as discussed in Appendix E of the main report.

Glazing

• Compliance with the Building Standards (Scotland) Regulations required glazing fittings in dwellings to achieve a U-value between 1.8 and 3.3 W/m ².K, depending on the amendment version of the regulations and a number of other factors.
• The U-value detailed in table S14 of Appendix S for double glazing in Scotland installed post 2003, as specified by the 1990 baseline standards, is 2.0 W/m ².K which tends towards the more stringent end of the U-value range detailed above.

Electric heated dwellings
Space and water heating

• The electric heated dwellings in case study group H specify factory applied foam insulation thickness of 38mm for the hot water cylinder. This corresponds to the default performance assumed by RdSAP for hot water cylinders in 1999-2007 constructed Scottish dwellings.

Gas heated dwellings
Space and water heating

• Unless specific data can be entered with regards to the efficiency for the specific make and model of the boiler, reference will need to be made to table 4b in SAP (v9.90).
• The 1990 baseline assumes a combi-gas boiler, installed in 1998 or later. Systems installed after 2005 are likely to be condensing systems, for which table 4b specifies an efficiency of 80-84%. For non-condensing systems installed prior to 2005, table 4b specifies an efficiency of 70-74%, however based on the building standards in place for the latter half of the construction period, and default RdSAP U-values, the boiler efficiency should be assumed to be greater than 78%.
• Where the construction U-values are determined from the RdSAP age band I, a winter seasonal efficiency of 74% seems appropriate.
• The specified controls for the 1990 baseline mean the system does not qualify for any efficiency adjustments, unless it features a boiler interlock, where a 5% reduction would apply.

Recommendations:

• The construction U-value specifications should operate on the basis of the default assumptions associated with RdSAP age band I, spanning the construction period between 1999 and 2002.
• Where the earlier construction period applies, a winter boiler efficiency of 74% is recommended.

Case Study Group G: Further Measures 2020

• The EESSH outlines a minimum EI rating to be achieved for electric and gas fuelled properties. These 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.
• The 1990 baseline specifications mean all the electric and gas heated dwellings in case study group H exceed the minimum SAP and EI rating, with the exception of the gas heated case study 21G.
• Only case study 21G is reliant on the specification of additional measures to meet compliance with the EESSH, however improvements are considered for all the case studies in group H under the 'further measures 2020 improvement stage.

Roof

• Where applicable, the loft insulation is increased to a thickness of 250mm for both the electric and gas heated dwellings.

Electric Heating
Space and water heating

• The proposed fan storage heaters, applicable to all the electric heated case studies, will have the same efficiency as the previous system, but will benefit from increased 'responsiveness' ^[22] and automatic controls. This will contribute to a reduction in the space heating requirement, and consequently an improved EI rating.
• The improvement to the hot water tank insulation, increasing the factory applied foam insulation thickness 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
Space and water heating

• The indicative life expectancy for a condensing boiler is in the region of 15 years ^[23] , therefore installation of a new system is appropriate for the 'Further Measures 2020' improvement stage. This also provides an opportunity to upgrade the control strategy.
• 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:

• 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 H: Advanced Measures 2050

• 'Advanced measures 2050' are only considered for case studies 22 and 23, both electric and gas heated.

Renewables: Solar PVs to 20% of roof

• Photovoltaic technology 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).
• Considered independent of any other improvement measures, landlords can view the potential benefits associated with this technology should it be suitable for any of the dwellings featured in their stock.

Recommendations:

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