Developing regulation of energy efficiency of private sector housing (REEPS): modelling improvements to the target stock - Main Research Report

8 Appendix 2: Methods, Assumptions and Default U-Values Of The 38 Measures

8.1 This appendix describes the methods, assumptions and default U-values used in the modelling of the 38 improvement measures.

M1. Loft insulation, including top up

8.2 The starting point for the loft insulation was taken as thickness of the insulation identified by the SHCS, which was then converted to a U-value as per Table S9 in Appendix S of the SAP 2012 manual. Where there was no access to the loft, the U-value was taken from Table S10 of Appendix S (which effectively assumes that the amount of loft insulation is compliant with the Building Regulations prevailing when the dwelling was first constructed).

8.3 Where the thickness of the loft insulation was 150mm or less, it was assumed that it would be topped up to 300mm of mineral fibre quilt (or an equivalent material) being installed in part between the joists and in part cross laid over the joists. The default U-value for 300mm of loft insulation is 0.14 W/m2K.

8.4 Where the existing loft insulation was more than 150mm, an upgrade to 300mm was only occasionally modelled.

8.5 Additional loft insulation was not recommended (as it was already present when more than 200mm of insulation was identified by the SHCS).

8.6 Not applicable: the dwelling does not have a pitched roof to insulate, e.g. ground and mid floor flats, and houses and bungalows with only flat roofs.

M2. Flat roof insulation

8.7 The starting point for the flat roof insulation was the SHCS identifying the roof structure of the main dwelling (occasionally) or an extension (more common) as a flat roof. Here, it would not be expected that the surveyor would be able to determine whether there was any insulation or not, so the U-value taken from Table S10 of Appendix S (which effectively assumes that the amount of flat roof insulation complies with the Building Regulations prevailing when the dwelling or the extension was constructed).

8.8 Where the flat roof was assumed to be uninsulated (i.e. with a U-value of 2.3 W/m2K) it was assumed to be improved with 100mm of high density insulation board (i.e. with a thermal conductivity of 0.022) in a warm deck structure to achieve a U-value of 0.2 W/m2K. This was a calculated U-value.

8.9 In most instances where flat roof insulation was modelled this was in an extension.

8.10 Not applicable: the dwelling does not have a flat roof to insulate, e.g. ground and mid floor flats, and houses and bungalows with only pitched roofs.

M3. Room in the Roof Insulation

8.11 Rooms in the roof come in different shapes, sizes and configurations, with and without dormers. What constitutes a room in the roof is defined in Section 3.3.5 of the SAP 2012 manual and Section S3.2 in Appendix S. RdSAP allows for a simple method of dealing with a dwelling with rooms in the roof by simply measuring the floor area, and letting RdSAP calculate the separate components of the room in the roof (i.e. the flat ceiling, the slopes, the stud walls, the gable walls, and the residual roof area for the main dwelling - Figure A2.1 below) by equations set out in Section S3.9 of Appendix S.

Figure A2.1: Components of Room in the roof

8.12 The U-values that RdSAP assign the individual components of the room in the roof are determined by the age of the room in the roof and the presence of any insulation. The default U-values are set out in Tables S9 and S10 of Appendix S (i.e. the same tables that define the default U-values for roof insulation). So a room in the roof (built before 1965) with no insulation seen during the SHCS survey, or where there is no access to allow the insulation to be assessed, would have a U-value of 2.3 W/m2K assigned to all of the individual components of the room. These U-values would improve in dwellings built later. Where insulation levels of the individual components can be determined then this insulation can be accommodated in RdSAP.

8.13 The basis of the room in the roof formula (i.e. a rectangular room-in-roof area of average height 2.2m) is defined in Section S3.9 of Appendix S. Further guidance is provided in the separate RdSAP Conventions document. Where a room in the roof deviates significantly from this model (e.g. with dormers comprising more than 20% of the roof area) RdSAP allows for the individual components to be measured separately and included in the RdSAP assessment.

8.14 The SHCS follows the simple RdSAP method for dealing with rooms in the roof by collecting the floor area of the room in the roof, though it also collects the storey height.

8.15 As the archetypes were modelled in SAP 2012, the areas and U-values of the individual components of the room in the roof had to be entered separately into the SAP program. These were obtained by entering the room in the roof floor area into an RdSAP 2009 v9.91 program and recording the respective areas and U-values of the individual components derived by the RdSAP program and then entering these values into the SAP 2012 program. The gable wall of the room in the roof U-value was adjusted to match the U-value of the main dwelling walls. The flat ceiling of the room in the roof was assumed to be insulated to the standard of the residual ceiling of the storey below.

8.16 For improvements to the individual components of the room in the roof, it was assumed that at least 100mm of insulation was added to the slopes, stud walls and gable wall components of the room in the roof, and the insulation of the flat ceiling was increased to 300mm. RdSAP would assume that all of this insulation had a thermal conductivity of 0.04 W/mK, with the resultant U-values in the previously uninsulated rooms in the roof built before 1965 of 0.14 W/m2K being achieved in the flat ceiling, and 0.40 W/m2K being achieved in the stud walls, slopes and gable walls.

8.17 The modelling also assumed that where room in the roof insulation was being carried out that the loft insulation in the residual loft area was insulated as well as part of the job.

8.18 In deriving its default U-values for the insulation of the rooms in the roof, RdSAP does not distinguish between whether this insulation is added to the internal face of the room in the roof components, or if the insulation is added to roof void side of the component.

8.19 RdSAP, within its convention protocols, does allow assessors to double the thickness of the insulation recorded within an RdSAP assessment where high density insulation materials such as polyurethane (aka PUR) or polyisocyanuarte (aka PIR) insulation materials are used, and can be documented. So, notionally, the default U-value of 0.4 W/m2K could also be achieved with 50mm of PIR or PUR insulation board being applied to the individual room in the roof components. If 100mm of such insulation material was installed, this would be recorded as having a thickness of 200mm in RdSAP 2012, and the default U-value from Table S9 of Appendix S would be 0.21 W/m2K.

8.20 Not recommended: where the dwelling had a room in the roof, insulation was in dwellings constructed after 1991 (as the assumption being these spaces were insulated already).

8.21 Not applicable: dwelling does not have a room in the roof.

M4. Cavity Wall insulation

8.22 The starting point was taken as the SHCS survey identifying the dwelling as having a masonry wall with a cavity that showed no indication of having been insulated. The SAP default U-value for such a wall is determined by the age of the construction, and set out in Table S7 of Appendix S (see the row 'Cavity as built'). For the largest percentage of dwellings with unfilled cavities (built between the 1920s and 1975) the default U-value would 1.6 W/m2K. Later age bands have a lower starting U-value, reflecting the impact of the Scottish Building Regulations.

8.23 Where cavity wall insulation was assessed, the improved U-value was again taken from Table S7, but from the row 'Filled cavity'. Where the starting point was 1.6, this would improve the U-value to 0.5 W/m2K. Later age bands would achieve a slightly lower U-value.

8.24 The party walls were not assumed to be insulated as part of any of the improvement measures.

8.25 It is possible that the default U-values for cavity wall insulation will underestimate the potential impact of this improvement measure, as the defaults are based on a 50mm cavity being filled with blown fibre with a thermal conductivity of 0.04 W/mK. Many cavities in Scotland are wider than 50mm so more insulation could be injected into them. Secondly, many installers are beginning to use bead materials with a lower thermal conductivity (e.g. silver bead with a thermal conductivity of 0.032 W/mK). Using a U-value calculator, insulating a cavity wall with a 50mm cavity with blown fibre material with a thermal conductivity of 0.04 W/mK would achieve a U-value of 0.58 W/m2K, while the same wall being insulated with 70mm of silver bead would achieve a U-value of 0.38 W/m2K. In such circumstances, RdSAP would expect the U-values to be calculated and the defaults to be over-written.

8.26 There are a number of stone wall archetypes where cavity wall insulation was assessed as an improvement option, not because the modelling assumed the stone walls were being filled, but because the dwellings had extensions with cavity walls that were surveyed as being not insulated.

8.27 Not recommended: if there was a cavity wall construction that was identified as being uninsulated then cavity wall insulation was always assessed.

8.28 Not applicable: no cavity wall.

M5. Solid Wall insulation

8.29 The starting point was taken as the SHCS survey identifying the wall construction as sandstone, granite, whinstone, solid brick or system built, and that there was no cavity within the wall construction. Such walls would need insulation applied to either the external face or the internal surface if their thermal performance was to be improved. The default U-values would be dependent on the age of the dwelling and the wall construction, as set out in Table S7 of Appendix S. With sandstone, granite and solid brick walls, the U-value is adjusted if an internal air gap is present (e.g. lathes and plaster or plasterboard on battens or dabs). The U-value for uninsulated pre -1976 sandstone and granite walls are further adjusted for the thickness of the wall (according to equations set out in Section S5.1.1 of Appendix S).

8.30 Where these walls had no insulation added already (some did, and were identified as 'already present'), it was assumed that 100mm of wall insulation was added to the external wall. In RdSAP, the application of 100mm of wall insulation produces a default U-value of 0.35 W/m2K with pre-1976 sandstone, granite, solid brick and system built walls (see Table S7 of Appendix S) regardless of whether the insulation is applied to the internal or external surface of the wall. The default U-value of 0.35 W/m2K was used in the modelling of solid wall insulation where it was assessed as an improvement measure for an archetype.

8.31 RdSAP makes no specific determination on the type of material used in insulating a solid wall, other than set out that the basis of the default U-value improvement for solid wall insulation is 100mm of a material with a thermal conductivity of 0.04 W/mK. So this default improvement could be achieved by installing 100mm of mineral wool, or 100mm of sheep's wool, or 100mm of cellulose fibre insulation.

8.32 RdSAP, within its convention protocols, does allow assessors to double the thickness of the insulation recorded within an RdSAP assessment where high density insulation materials such as polyurethane (aka PUR) or polyisocyanuarte (aka PIR) insulation materials are used, and can be documented. So, notionally, the default U-value of 0.35 W/m2K could also be achieved with 50mm of PIR or PUR insulation board. If 100mm of such insulation was installed, it would be recorded as having a thickness of 200mm in RdSAP 2012, and the default U-value would be reduced to 0.18 W/m2K.

8.33 RdSAP also makes no determination on whether the insulation installed needs to be 'vapour open' or 'vapour closed'.

8.34 Not recommended: From the information available to the modelling exercise there was no reason to not recommend solid wall insulation where the dwelling was constructed of one of these wall types and it was not already insulated. Contraindications to not carrying out solid wall insulation would need to be identified onsite.

8.35 Not applicable: the dwelling was not constructed from one of the solid wall constructions.

M6. Floor Insulation

8.36 The starting point was taken as the SHCS survey identifying the floor construction and the presence of any insulation. In RdSAP, the calculation of the floor U-value also takes account of the exposed perimeter to floor area ratio of the heat loss ground floor. Each existing heat loss floor U-value was calculated individually by putting these details into an RdSAP 2009 v9.91 program, and the resultant U-value noted.

8.37 For the improvement measure, only dwellings with uninsulated heat loss ground floors were assessed (so upper floor flats were not assessed, nor were exposed floor areas over passageways in mid-terrace dwellings).

8.38 For an uninsulated suspended timber floor, it was assumed that 100mm of insulation quilt was fitted between the joists below the floor and suspended on netting.

8.39 For solid floors, it was assumed that 50mm of insulation with a hard finish was fitted on top of the existing solid floor.

8.40 RdSAP assumes the insulation to have a thermal conductivity of 0.4W/mK. Each U-value resulting from the addition of the floor insulation was re-calculated in RdSAP, and then entered into the full SAP assessment.

8.41 Not recommended: from the information available to the modelling exercise there was no reason to not recommend floor insulation where the dwelling had a heat loss ground floor and it was not insulated. If it was insulated this was recorded as 'already present'.

8.42 Not applicable: only where there was no heat loss ground floor present: mid and top floor flats.

M7. Double Glazing to a U-value of at least 1.8 W/m2K; M8. Secondary Glazing to a U-value of 2.4 W/m2K; and M9 Triple Glazing to a U-value of at least 1.4 W/m2K

8.43 The extent of multiple glazing within a dwelling, and the type of multiple glazing (see Table S14 of Appendix S) is assessed during the SHCS. The frame type is also assessed in the SHCS which has implications in full SAP but has been ignored in RdSAP until RdSAP v9.92 was introduced in December 2014.

8.44 Where the dwelling had single glazing, then all three multiple glazing options were assessed. The U-value of 2.4 W/m2K for secondary glazing is the RdSAP default.

8.45 The double glazing U-value of 1.8 W/m2K comes from Table 6e of the SAP manual and notionally represents a wood or uPVC-framed double glazed unit with a 16mm gap and soft coat low-emissivity coating, and is argon filled. Other double glazing permutations exist in Table 6e that would achieve the same U-value.

8.46 The triple glazing U-value of 1.4 W/m2K also comes from Table 6e of the SAP manual, and notionally represents a uPVC or wood framed triple glazed unit with a 16mm gap and soft coat low-emissivity coating, and is argon filled. Again, other triple glazing permutations exist in Table 6e that would achieve the same U-value.

8.47 RdSAP conventions allow for the U-values from Table 6e of the SAP manual to be used in the program, and are not just limited to those in Table S14 in Appendix S.

8.48 Better performing glazing units exist in both Table 6e and on the open market.

8.49 If the dwelling had uPVC or wood framed pre-2003 double glazing already, then only the triple glazing option was assessed.

8.50 If the dwelling had pre-2003, metal frame double glazing, which in full SAP has a higher U-value than the RdSAP default of 3.1 W/m2K for double glazing, then double and triple glazing were assessed as improvement options.

8.51 Not recommended: if the dwelling had post-2002 double glazing, then no alternative glazing measure was assessed. The small improvement in the U-value would have made this a very expensive option for a very small gain, if any gain at all, in the SAP score.

8.52 From the information available to the modelling exercise there was no reason to not recommend secondary, double or triple glazing as appropriate. However, these options may not be available for dwellings in conservation areas or in listed buildings. The SHCS does not collect that information about the property.

8.53 Not applicable: not an option here. Assessing the measure as an improvement, or recording it as not recommended or already present covered all of the options.

M10. Insulated External Doors

8.54 All external doors were assumed to be uninsulated solid wood external doors with a default U-value of 3.0 W/m2K. The SHCS does not collect specifically this data item, therefore under RdSAP conventions, unless documentation is available to the contrary, then surveyors are to assume that the doors are not insulated. A house was assumed to have 2 external doors; a flat was assumed to have 1 external door and located in the unheated corridor wall (if this was present in the flat). These are the RdSAP defaults prior to doors being counted in RdSAP v9.91 (i.e. after October 2012).

8.55 Insulated doors were assumed to achieve a U-value of 1.0 W/m2K. In RdSAP, if insulated doors are included then the U-value must be entered into the program.

8.56 Insulated doors were assessed in all instances.

M11. Hot Water Tank Jacket 80mm

8.57 The SHCS collects data on the type of insulation (spray foam or jacket) and its thickness on a dwelling's hot water cylinder. Where there was no access to the hot water cylinder, then the RdSAP defaults were used. These are set out in Table S17 and Table S18 of the SAP 2012 manual, and are dependent upon the installed heating and the age of the property

8.58 Where the hot water cylinder was uninsulated, then an 80mm jacket was modelled.

8.59 Where the existing cylinder insulation was a jacket of 50mm or less, an additional 80mm jacket was added on top of the existing jacket.

8.60 Where the existing cylinder was 40mm of spray foam or less, an additional 80mm jacket was added over the existing spray foam. This is modelled in RdSAP by increasing the thickness of the spray foam by half the thickness of the insulating jacket (i.e. by increasing the thickness of the spray foam by 40mm) as spray foam is considered twice as effective at retaining heat as a jacket.

8.61 Not recommended: from the information available to the modelling exercise there was no reason to not recommend insulation of the hot water tank where it was present and not already insulated as set out above. If it was insulated as not above, then it was recorded as already present.

8.62 Not applicable: given the prevalence of combi boilers within the Scottish dwelling stock, this was a common occurrence within the data set.

M12. Draughtproof Windows and Doors

8.63 The SHCS data set does not include information on whether windows and doors are draughtproofed as this item was only introduced into RdSAP in Scotland with version 9.91 from October 2012, i.e. after the current SHCS survey form had been designed. So the RdSAP 2009 v9.90 assumptions were used in the modelling of the archetypes - if the windows are double glazed then the assumption is that they are draughtproofed; if they are single glazed then the assumption is that they are not draughtproofed (with the exception of post-1991 dwellings with single glazing as the Building Regulations would have required them to be draughtproofed).

8.64 Doors were assumed not to be draughtproofed unless a dwelling was built post-1991, or the dwelling had post-2002 double glazing fitted on the assumption that the household upgraded the door at the same time. This would be recorded as 'already present'.

8.65 While this measure was commonly applied within the modelling of the archetypes, it often only applied to the draught proofing of the doors, so in houses, 2 doors; in flats, 1 door, and therefore of limited impact. Where the windows in these houses were surveyed as having double or triple glazing of any type, they were recorded as being draught proofed.

8.66 Not recommended: from the information available to the modelling exercise there was no reason to not recommend the draught proofing of doors and single glazed windows. Within listed buildings, the draught proofing of windows may be restricted.

8.67 Not applicable: not an option here: either draught proofing was already present or it was modelled.

M13. Fit Baffle / Damper to open fire

8.68 The SHCS records the number of open fireplaces in a dwelling, as does RdSAP, which has an effect of increasing the dwelling's ventilation rate: the more open fireplaces, the greater the increase in the ventilation rate, and thus the greater the calculated energy consumption.

8.69 Fitting a baffle / damper (a device for closing down the chimney when the open fire is not being used, thus reducing the air infiltration via the chimney) to the open fireplace reduces the ventilation losses (in full SAP, this is done by converting the open fireplace to a flue, and in RdSAP, by reducing the count of open fireplaces).

8.70 Fitting a baffle / damper to the open fireplace does not reduce its usability as an open fire.

8.71 Not recommended: from the information available to the modelling exercise there was no reason to not recommend fitting a baffle / damper to an open fire if an ope fire place was present and did not have a baffle / damper already fitted. It would not be possible to identify 'already present' from the data, as the RdSAP conventions and SHCS guidelines to surveyors deem open fireplaces with a damper to be recorded as a flue.

8.72 Not applicable: there were no open fireplaces in the property.

M14. Replace gas boiler with 88% efficient condensing boiler

8.73 For this option to be modelled the dwelling must have already had a non-condensing gas boiler central heating system installed, whether it be a regular boiler, combi boiler, or a back boiler.

8.74 The assumption here was that this improvement was a boiler only replacement, with respectively a condensing regular, combi or back boiler with a minimum SAP 2009 efficiency of 88% being installed. For the condensing back boiler, the actual efficiency used was 88.8% (i.e. the SAP 2009 efficiency for the Baxi BBU 15HE, the only condensing gas back boiler on the market known to the contractor).

8.75 Not recommended: should not be an option. If there was an existing condensing boiler within the dwelling, then it was recorded as 'already present'.

8.76 Not applicable: no gas boiler present.

M15. Replace oil / LPG boiler with 90% efficient condensing boiler

8.77 For this option to be modelled the dwelling must have already had a non-condensing oil or LPG boiler central heating system installed, whether it be a regular boiler or combi boiler.

8.78 LPG boilers can achieve a higher efficiency than mains gas boilers, thus were included in this option rather than in improvement M14.

8.79 The assumption here was that this improvement was a boiler only replacement, with respectively a condensing regular or combi or back boiler with a minimum SAP 2009 efficiency of 90% being installed.

8.80 Not recommended: should not be an option. If there was an existing oil or LPG condensing boiler within the dwelling, then it was recorded as 'already present'.

8.81 Not applicable: no oil or LPG boiler present.

M16. Full Gas Central Heating System including controls

8.82 Where the dwelling does not already have a central heating system, but has a mains gas meter, this improvement includes for fitting a mains gas condensing combi boiler with a SAP 2009 efficiency of at least 88% and a radiator system. The controls include for a programmer, room thermostat and thermostatic radiator valves (TRVs) to be fitted as well.

8.83 An example of a mains gas regular boiler that meets this criterion is the Hoval Top Gas 35 boiler, identified through the Product Characteristic Database, reference number 017241.

8.84 An example of a mains gas combi boiler that meets this criterion is the Sime Planet Dewey 90 boiler, identified through the Product Characteristic Database, reference number 008605.

8.85 There are other boilers within the Product Characteristic Database that meet this criterion, or have a higher efficiency.

8.86 Not recommended: should not be an option. If there was an existing condensing boiler within the dwelling, then it was recorded as 'already present'.

8.87 Not applicable: no gas central heating and no gas meter present.

M17. Full Oil or LPG Central Heating System including controls

8.88 Where the dwelling does not already have a central heating system, and there is no mains gas meter, this improvement includes for fitting an oil or LPG condensing combi boiler with a SAP 2009 efficiency of at least 90% and a radiator system. The controls include for a programmer, room thermostat and thermostatic radiator valves (TRVs) to be fitted as well.

8.89 An example of an oil regular boiler that meets this criterion is the Aquaflame HE22 boiler, identified through the Product Characteristic Database, reference number 008386.

8.90 An example of an oil combi boiler that meets this criterion is the Grant Engineering Horizon Combi 26, identified through the Product Characteristic Database, reference number 017163.

8.91 An example of a LPG regular boiler that meets this criterion is the Viesmann Vitodens 100-W WB1C 30KW, identified through the Product Characteristic Database, reference number 017002.

8.92 An example of a LPG combi boiler that meets this criterion is the Valliant Ultracom 2 24cxi, identified through the Product Characteristic Database, reference number 016326.

8.93 There are other boilers within the Product Characteristic Database that meet this criterion, or have a higher efficiency.

8.94 Not recommended: should not be an option. If there was an existing condensing boiler within the dwelling, then it was recorded as 'already present'.

8.95 Not applicable: no central heating but a gas meter present.

M18. Full Biomass Central Heating System including controls

8.96 Where the dwelling does not already have a central heating system, there is no mains gas supply, and the household is already using solid fuel for their heating, this improvement includes for fitting a wood pellet boiler with a SAP 2009 efficiency of 88.4% and a radiator system. The controls include for a programmer, room thermostat and thermostatic radiator valves (TRVs) to be fitted as well.

8.97 An example of a boiler that meets this criterion is the Grant Engineering Spira 9-36 boiler, identified through the Product Characteristic Database, reference number 700019.

8.98 Not recommended: a biomass system was not assessed as an improvement where the dwelling type was a flat because of the storage needs associated with the wood pellets.

8.99 It was also not recommended where other non-solid fuel heating systems were already installed.

8.100 Not applicable: not an option here. The reasons for not assessing the installation of biomass heating system for every archetype were covered in para 8.98 'Not recommended' and para 8.99.

M19. Fan Electric Storage Heaters with Auto Charge Control

8.101 Where the dwelling already has old block electric storage heating, or more modern slimline electric storage heaters, this improvement assesses replacing them with the more responsive fan storage heaters. Rather than rely on manual charge control (that is, the householder predicting the following day's weather and adjusting the charge level every night) the dwelling is fitted with a weather compensation system. Alternatively in Scotland, they may connect to SSE's Total Heating Total Control tariff or ScottishPower's Weathercall system (both of which utilise dynamic radio-teleswitching to remotely vary the charge level in response to changes in the weather).

8.102 Not recommended: electric storage heating was not recommended where there was a gas or oil central heating system or a solid fuel / wood boiler system present as the change would significantly reduce the SAP rating.

8.103 Not applicable: not an option here. As all of the archetypes assessed were connected to the electricity grid, electric heating could be installed and therefore be assessed as an option. However, assessing the installation of electric heating was not assessed for every archetype for the reasons set out in para 8.102 'Not recommended'.

M20. Quantum Storage Heaters

8.104 'Quantum' is Dimplex's product name for the High Heat Retention Electric Storage Heaters that have been included in SAP 2012 and RdSAP 2012 for the first time. The claim is that they are 27% cheaper to run than comparable static storage heaters, and consume 22% less energy for achieving the same comfort conditions in the dwelling. They have in-built programmers and thermostats.

8.105 These storage heaters can only be selected in SAP 2012 and RdSAP 2012 via the Product Characteristic Database. Two other companies' high heat retention storage heaters are also listed (i.e. Creda and Heatstore) but they are also referred to as 'Quantum' heaters.

8.106 Not recommended: 'Quantum' storage heating was not recommended where there was a gas or oil central heating system or a solid fuel / wood boiler system present as the change would reduce the SAP rating.

8.107 Not applicable: not an option here. As all of the archetypes assessed were connected to the electricity grid, electric heating could be installed and therefore be assessed as an option. However, assessing the installation of electric heating was not assessed for every archetype for the reasons set out in para 8.106 'Not recommended'.

M21. Full Electric Radiator System including controls on an off-peak tariff

8.108 Effectively, direct acting room heaters with individual appliance thermostats coupled, importantly, with a programmer and possibly a room thermostat, with the electricity charged on a 10-hour cheap rate tariff. It is the connection to the off peak tariff that gives them an advantage over direct electric heating. The 10 hours of the cheap rate is usually broken up over 3 periods over the day.

8.109 Unlike electric storage heaters, these systems do not have a storage capacity, and there may be times during the day when they may run on the more expensive part of the electricity tariff if use is not well controlled by the programmer.

8.110 Not recommended: an electric radiator system was not recommended where there was a gas or oil central heating system or a solid fuel / wood boiler system present as the change would reduce the SAP rating. Also not recommended where there was already electric storage heating.

8.111 Not applicable: not an option here. As all of the archetypes assessed were connected to the electricity grid, electric heating could be installed and therefore be assessed as an option. However, assessing the installation of electric heating was not assessed for every archetype for the reasons set out in para 8.110 'Not recommended'.

M22. Air Source Heat Pump: Air to water with full zone control

8.112 Heat pumps extract heat from the environment and then through a process of compression and expansion pass this heat into the dwelling. The great attraction of heat pumps is that they draw their heat for free and therefore you are only paying for the pumps and compressors to drive the system, so that you can notionally get more energy out of the system (as heat output) than you pay for to run the system (i.e. if it is well designed). Heat pumps operate most efficiently when the source temperature is as high as possible and the heat distribution temperature is as low as possible.

8.113 Here, the heat source would be the air. As this heating system would be installed in an existing dwelling then the heat distribution would be via radiators, so the heat would be transferred to the water circulating through the radiators which has implications for reducing the performance of the systems.

8.114 The controls would enable different areas of the dwelling to be programmed for the heating to be used at different times and to achieve different temperatures.

8.115 Not recommended: an air source heat pump system was not recommended where there was a gas or oil central heating system or a solid fuel / wood boiler system present as the change would reduce the SAP rating. Also, this option was not recommended where there was already electric storage heating.

8.116 Not applicable: not an option here. As all of the archetypes assessed were connected to the electricity grid, electric heating could be installed and therefore be assessed as an option. However, assessing the installation of electric heating was not assessed for every archetype for the reasons set out in para 8.115 'Not recommended'.

M23. Ground Source Heat Pump: Ground to water with full zone control

8.117 An alternative form of heat pump to the air source heat pump set out in M22. Here, the heat source is the ground, with the heat being gathered via a vertical bore hole or via coils buried horizontally in the ground. The latter approach would require the dwelling to have the necessary land area surrounding the dwelling in which to bury sufficient lengths of the coils to extract enough heat.

8.118 Again, as this heating system would be installed in an existing dwelling then the heat distribution would be via radiators, so the heat would be transferred to the water circulating through the radiators which has implications for reducing the performance of the systems.

8.119 The controls would enable different areas of the dwelling to be programmed for the heating to be used at different times and to achieve different temperatures.

8.120 Not recommended: ground source heat pump systems were not recommended where there was a gas or oil central heating system or a solid fuel / wood boiler system present. They were also not recommended where there was already electric storage heating. It was not recommended in any obviously urban setting because of the land requirements needed to bury the heat collecting pipes. It was not recommended for flats.

8.121 Not applicable: not an option here. The reasons for not assessing the installation of ground source heat pump for every archetype were covered in para 8.120 'Not recommended'.

M24. Room Thermostat for the heating system

8.122 Where a dwelling does not have a room thermostat, SAP and RdSAP assume that the lack of room thermostat will contribute to the heating system not switching off when the dwelling is up to temperature, that is, the dwelling will over-heat. With a wet central heating system, the lack of the room thermostat is assumed to contribute to the boiler cycling. Fitting a room thermostat reduces the possibility of the dwelling overheating and possibly the boiler cycling.

8.123 The presence of a room thermostat not only reduces the energy consumed in heating the dwelling by reducing overheating of the dwelling, but in tandem with a cylinder thermostat (on an indirect hot water system) is also assumed by RdSAP to improve the overall boiler efficiency by reducing cycling by the boiler (the presence of both a room thermostat and a cylinder thermostat on a wet central heating system are deemed to interlock the boiler).

8.124 Not recommended: this should not be an option, as either there is a room thermostat with a wet central heating or warm air system, and some electric radiator systems, so 'already present', or it is not applicable.

8.125 Not applicable: where there was an electric storage heating system or room heaters as the main form of heating.

M25. Programmer for the heating system

8.126 Where the dwelling does not have a programmer (or a time clock) to control when the heating comes on and goes off, the use of the heating is controlled simply by an off-on switch. Fitting a programmer allows the hours of operation of the heating system to be better controlled.

8.127 Not recommended: this should not be an option, as either there is a room thermostat with a wet central heating or warm air system, and some electric radiator and wet central heating systems, so 'already present', or it is not applicable.

8.128 During the modelling it was found that in some solid fuel systems, fitting a programmer made no difference at all in the energy performance of the dwelling.

8.129 Not applicable: where there was an electric storage heating system or room heaters as the main form of heating.

M26. Thermostatic Radiator Valves (TRVs)

8.130 Unlike a room thermostat which gives a centralised control over the dwelling temperature and can shut the boiler down when the dwelling is up to temperature, TRVs control the temperatures in individual rooms, and only shut down individual radiators. Fitting TRVs provide better control of temperature across the whole dwelling.

8.131 If the dwelling does not have a wet central heating system, then TRVs would not be recommended.

8.132 Not applicable: where there was an electric storage heating system, warm air systems, or room heaters as the main form of heating.

M27. Full Controls Package (room thermostat, programmer and TRVs)

8.133 Where the dwelling has no controls at all on a wet central heating system, then this package of controls would be recommended.

8.134 Not recommended: where some of the controls are present, or the type of installed heating system does not require this full package of controls (e.g. a warm air system would not need TRVs to be fitted) those missing would be recommended as individual improvements via M24, M25 and M26 as appropriate.

8.135 Not applicable: where there was an electric storage heating system, warm air systems, or room heaters as the main form of heating.

M28. Auto Charge Control

8.136 This improvement would only be recommended for an existing electric storage heating system currently reliant upon manual charge control.

8.137 Not applicable: with all other forms of heating

M29. Solar Thermal 4m2

8.138 Whether the dwelling has solar panels for hot water or not is one of the data items collected by the SHCS. Where the dwelling does not have solar panels, the surveyors record whether the dwelling is suitable for them to be fitted. The criteria they are given for this assessment are that the dwelling has 8m2 of roof area facing within 30o of south (which is assessed with a compass), and that they are not over-shaded by taller buildings. Where the SHCS assessment does not recommend fitting solar thermal panels, this improvement was not assessed.

8.139 Where the SHCS indicates that the dwelling is suitable, this improvement assessed fitting a 4m2 (gross area) glazed flat plate collector, assuming a south orientation, at a 30o roof pitch with average over shading. If the dwelling had a hot water cylinder, this was replaced with a 250 litre combined cylinder with 100 litres dedicated to solar heated water storage. This cylinder was assumed to be insulated with 50mm of spray foam.

8.140 If the dwelling did not have a hot water cylinder (e.g. where there was a combi boiler), then the solar thermal was assumed to have its own 100 litre store.

8.141 Not recommended: where SHCS indicated the dwelling was unsuitable for solar panels or already installed.

8.142 Not applicable: where the dwelling did not have its own roof, eg, ground and mid floor flats.

M30. Photovoltaic (PV) Panels - 2 kWp

8.143 Whether the dwelling has PV panels for generating electricity or not is one of the data items collected by the SHCS. Where the dwelling does not have PV panels, the surveyors record whether the dwelling is suitable for them to be fitted. The criteria they are given for this PV assessment are that the dwelling has 8m2 of roof area facing within 45o of south (which is assessed with a compass), and that they are not over-shaded by taller buildings. Where the SHCS assessment does not recommend fitting PV panels, this improvement was not assessed.

8.144 Where the SHCS indicates that the dwelling is suitable, this improvement assessed fitting a PV array with a rated output of 2 kWp, assuming a south orientation, at a 30o roof pitch with average over shading.

8.145 Not recommended: where SHCS indicated the dwelling was unsuitable for PVs or they were already installed.

8.146 Not applicable: where the dwelling did not have its own roof, e.g, ground and mid floor flats.

M31. 2m Diameter Wind Turbine on Roof of Dwelling

8.147 As long as the dwelling had its own roof (so ground and mid floor flats were excluded from this assessment), a small wind turbine, that is one with a blade diameter of 2m with the hub sitting 2m above the apex of the roof was assessed. As the output from a wind turbine varies depending on its location, then each archetype was assigned an urban, suburban or rural designation within SAP 2012 based on its original local authority area.

8.148 Not applicable: where the dwelling did not have its own roof, eg, ground and mid floor flats.

M32. 5m Diameter Wind Turbine on Stand-alone Mast

8.149 A larger wind turbine, that is, one with a blade diameter of 5m with the hub sitting 5m above the ground on its own stand-alone mast was assessed. Such a mast needs to be sited at a safe distance from the dwelling so this improvement was not assessed for all dwelling types (e.g. not with flats) or in all areas. As the output from a wind turbine varies depending on its location, then each archetype was assigned an urban, suburban or rural designation within SAP 2012 based on its original local authority area.

8.150 Not recommended: given the space requirements this option was not recommended in obviously urban areas.

8.151 Not applicable: not an option here. The reasons for not assessing the installation of a stand-alone wind turbine for every archetype were covered in para 8.150 'Not recommended'.

M33. 100% Low Energy Lighting

8.152 The SHCS assesses the percentage of light fittings within a dwelling fitted with low energy lighting. If there was less than 100% already, this improvement increased the percentage to 100%. For the sake of costing the improvement it was assumed that there was one light fitting in each room.

8.153 If the dwelling did not have 100% low energy lighting then this measure was assessed.

8.154 Not recommended: should not be an option, as either all the fixed light fittings had low energy lights already, so 'already present' or the measure was assessed.

8.155 Not applicable: not an option here, as either low energy was recommended or cover by para 8.154 'Not recommended'.

M34. Cylinder thermostat on hot water cylinder

8.156 The SHCS notes whether a cylinder thermostat is fitted to an indirect hot water cylinder. A cylinder thermostat would not be needed for other types of hot water supply: combi boilers do not have a hot water cylinder, while in SAP and RdSAP, where the primary water heating is provided by means of an electric immersion heater, the cylinder thermostat is assumed to be built into the immersion heater.

8.157 The presence of a cylinder thermostat (on an indirect hot water system) not only reduces the energy consumed in heating the hot water but in tandem with a room thermostat is also assumed by RdSAP to improve the overall boiler efficiency by reducing cycling by the boiler (i.e. the presence of both a room thermostat and a cylinder thermostat on a wet central heating system are deemed to interlock the boiler).

8.158 Not recommended: this should not be an option, as either there is a cylinder thermostat, so 'already present', or the measure was assessed, or it was not applicable.

8.159 Not applicable: with combi boilers, and electric immersion heaters and community heating, as RdSAP assumes all of these types of water heating include control of the water temperature.

M35. Air to Air Heat Pump on E10 tariff with full zone control

8.160 Another alternative to the two heat pumps set out above in M22 and M23.

8.161 Here, the heat source is air, but there is no radiator system, as the heat distribution is also via warm air. This could conceivably be a centralised air source heat pump distributing warmed air around the dwelling via ducting. As this heating system would be installed in an existing dwelling then it may be more appropriate to fit individual units into each room. The advantage of an air to air heat pump delivering warm air directly into a room, compared to an air to water source heat pump circulating warmed water through the radiators, is the improved performance because the air temperature does not have to be raised as high as water temperature to pass heat to the occupants.

8.162 The controls would enable different areas of the dwelling to be programmed for the heating to be used at different times and to achieve different temperatures.

8.163 Not recommended: an air source heat pump system was not recommended where there was a gas or oil central heating system or a solid fuel / wood boiler system present as the change would reduce the SAP rating. Also not recommended where there was already electric storage heating.

8.164 Not applicable: not an option here. As all of the archetypes assessed were connected to the electricity grid, electric heating could be installed and therefore be assessed as an option. However, assessing the installation of electric heating was not assessed for every archetype for the reasons set out in the paragraph above.

M36. More Efficient Room Heater

8.165 A number of dwellings were identified as reliant on solid fuel open fires as secondary heating with 32% efficiency rating in SAP and RdSAP, or even worse, mains gas decorative fuel effect fires open to the chimney with a 20% efficiency rating.

8.166 This option assessed replacing a solid fuel, open fire with grate with a HETAS-approved solid fuel stove with a 65% efficiency rating or fitting a solid fuel cassette (effectively, an insert into the fire place that converts the open fireplace into a closed room heater^[79] with the consequential improvement in the efficiency from 32% to 65%).

8.167 Where secondary room heater was the mains gas decorative fuel effect fire open to the chimney (with its 20% efficiency in SAP), the assumption was to replace it with a flush fitting fire sealed to the chimney with a 40% efficiency rating.

8.168 In a couple of dwellings with just one gas room heater, and portable electric heating became the primary or secondary (under SAP conventions where 25% or less of the habitable rooms have fixed room heaters, then portable electric heaters are to be modelled as primary heating; and where between 25% and 75% of the habitable rooms have fixed heating, then portable electric heating is to be modelled with direct electric as the secondary heating) adding additional gas fires to remove the portable electric heating from the assessment has significant benefits in SAP.

8.169 Not recommended: this should not be an option: where there was a solid fuel fire or gas coal effect fire open to the chimney the measure was assessed, or it was not applicable or 'already present'.

8.170 Not applicable: where the dwelling was not inadequately heated; where there was no solid fuel open fire; or where there was no gas or coal effect open to the chimney fire.

M37. Thermaflow Electric CPSU Boiler System

8.171 SAP 2012 and RdSAP 2012 now include an18-hour off peak tariff to assess electric combine primary storage unit (CPSU) wet central heating systems that were previously poorly rated because they were assessed on the wrong tariff. This tariff is only available in the Scottish Power supply area (i.e. Supply Area 18).

8.172 Where a dwelling was off the gas grid, without an existing central heating system, and its original local authority area was within the Scottish Power supply area, this option was assessed.

8.173 Not recommended: An electric wet central heating system was not recommended where there was a gas or oil central heating system or a solid fuel / wood boiler system present as the change would reduce the SAP rating. Also not recommended where there was already electric storage heating. Not recommended for areas falling outside Supply Area 18.

8.174 A few properties already had these systems installed, thus 'already present'

8.175 Not applicable: not an option here. As all of the archetypes assessed were connected to the electricity grid, electric heating could be installed and therefore be assessed as an option. However, assessing the installation of electric heating was not assessed for every archetype for the reasons set out in paragraph above.

M38. Tariff Switch

8.176 Both Scottish Power and SSE have available normal off-peak tariffs and 24-hour based tariffs for electric storage heating. Where a dwelling has an existing storage heating system, then the benefit of switching tariff was assessed. This tariff switch was only included in the improvements assessed if it resulted in an improvement in the SAP score of the dwelling.

8.177 There are also 10-hour off peak tariffs available for direct electric systems.

8.178 Not recommended: where after modelling the inclusion of the tariff switch for a type of electric heating the SAP rating went down.

8.179 Not applicable: where the heating was anything other than electric heating.