6.1 Carbon dioxide emissions

Mandatory Standard

Standard 6.1

Every building must be designed and constructed in such a way that:

  1. the energy performance is estimated in accordance with a methodology of calculation approved under regulation 7(a) of the Energy Performance of Buildings (Scotland) Regulations 2008 and

  2. the energy performance of the building is capable of reducing carbon dioxide emissions.

Limitation:

This standard does not apply to:

  1. alterations and extensions to buildings, other than alterations and extensions to stand-alone buildings having an area less than 50 square metres that would increase the area to 50 square metres or more, or alterations to buildings involving the fit-out of the building shell which is the subject of a continuing requirement

  2. conversions of buildings

  3. non-domestic buildings and buildings that are ancillary to a dwelling that are stand-alone having an area less than 50 square metres

  4. buildings, which will not be heated or cooled, other than by heating provided solely for the purpose of frost protection or

  5. limited life buildings which have an intended life of less than 2 years.

6.1.0 Introduction

Standard 6.1 focuses on the reduction of carbon dioxide emissions arising from the use of heating, hot water and lighting in a new dwelling. The guidance sets an overall level for maximum carbon dioxide emissions in buildings by use of a methodology which incorporates a range of parameters that influence energy use. This means that, for new dwellings, a designer is obliged to consider energy performance as a complete package rather than looking only at individual elements such as insulation or boiler efficiency - a ‘whole dwelling approach’ to energy, which offers a significant degree of design flexibility.

For the majority of new buildings, Standard 6.1 has the greatest influence on design for energy performance. Standards 6.2 to 6.10, in the main, recommend benchmark and backstop levels to be achieved for individual elements or systems. To achieve compliance with Standard 6.1 it will be necessary to improve on these backstop levels or incorporate additional energy efficiency measures, such as low carbon equipment (LCE).

Directive 2009/28/EC http://europa.eu/legislation_summaries/energy/renewable_energy/en0009_en.htm promotes the use of energy from renewable sources. Where the building design will include use of renewable energy for heating, Article 13 of the Directive recommends, amongst other measures, consideration of use of the following:

  • for biomass equipment, conversion efficiencies of 85%

  • for heat pumps, those that fulfil the minimum requirements of eco-labelling established in Commission Decision 2007/742/EC of 9 November 2007 establishing the ecological criteria for the award of the Community eco-label to electrically driven, gas driven or gas absorption heat pumps and

  • for solar thermal systems, those that are subject to EU standards, including eco-labels and other technical reference systems established by the European standardisation bodies.

Directive 2010/31/EU http://eur-lexhttp//.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:153:0013:0035:EN:PDF requires that, for all new buildings, the technical, environmental and economic feasibility of high-efficiency alternative systems (such as decentralised energy supply systems using renewable energy, co-generation, district or block heating/cooling and heat pumps) are considered and taken into account in developing proposals.

This should be documented and available for verification purposes and a statement should therefore accompany the building warrant application. Further information on this process is available in the guidance note EPC 10 - 'Consideration of high-efficiency alternative systems in new buildings'. http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/enerperfor

Conversions - in the case of conversions as specified in regulation 4, this standard does not apply.

6.1.1 Dwellings

Objective - the calculated carbon dioxide emissions (measured in kilograms per square metre of floor area per annum) for the proposed dwelling, the dwelling emissions rate (DER), should be less than or equal to the target carbon dioxide emissions for a ‘notional dwelling’, the target emissions rate (TER).

Summary of procedure - in order to establish the target carbon dioxide emissions rate (TER) for the ‘notional dwelling’ (i.e. a dwelling of the same size, shape and 'living area fraction' as the proposed dwelling), the dimensions and 'living area fraction' of the proposed dwelling and a set of standard values are input into the methodology. To calculate the emissions for the proposed dwelling (DER) a second calculation is carried out where the proposed values are input into the methodology. An alternative way of meeting Standard 6.1 which avoids the use of the calculation methodology is to design to the set of values used for the ‘notional dwelling’. This elemental approach is described in clause 6.1.6.

The Government’s Standard Assessment Procedure for Energy Rating of Dwellings (SAP 2009) http://www.bre.co.uk/sap2009/page.jsp?id=1642 is the calculation tool used with the methodology which conforms with the European Directive 2002/91/EC http://europa.eu/legislation_summaries/other/l27042_en.htm and is approved to calculate the energy performance and the carbon dioxide emissions of an individual dwelling. At all stages, the conventions in the SAP document should be read in conjunction with the specific guidance given in the clauses to this section.

Non-domestic use within dwellings - some new dwellings may incorporate surgeries, consulting rooms, offices or other accommodation of a floor area not exceeding 50m² in aggregate, used by an occupant of the dwelling in a professional or business capacity. Where this occurs, the accommodation should be considered as a part of the dwelling.

6.1.2 Setting the target carbon dioxide emissions level

To set the target carbon dioxide emissions level, (i.e. the level that should not be exceeded, the TER), refer to the table to this clause. The package of measures for the fuel type for the main space heating of the proposed dwelling is selected. This package of measures is used in the methodology and no improvement factors are applied. In addition, this ‘notional dwelling' is to have the same size, shape (including floor, roof, exposed wall areas and storey heights) and 'living area fraction' as the proposed dwelling. These terms are explained in SAP 2009.

Software vendors providing BRE - approved SAP 2009 software http://www.bre.co.uk/ will incorporate a function that, with ‘Scotland’ selected, automatically generates the target CO2 emissions level once the fuel type is selected and the ‘notional dwelling’ dimensions and 'living area fraction' have been input into the programme.

Measures to calculate target carbon dioxide emissions for the 'notional dwelling'

The measures identified in this table are set to deliver on aggregate, 30% fewer carbon dioxide emissions than the 2007 Standards. Whilst it is possible to construct a dwelling using one of the packages of measures (see clause 6.1.6), this table is provided for the purpose of setting the target emission rate (TER) for the ‘notional dwelling'.

Table 6.1. Main space heating system fuel [1] [2]

Element or system Gas (Package 1) LPG (Package 2) Oil (Package 3) Electricity (Package 4) Biomass [3] (Package 5)
Walls U = 0.19 U = 0.19 U = 0.19 U = 0.19 U = 0.19
Floors U = 0.15 U = 0.15 U = 0.15 U = 0.15 U = 0.15
Roofs U = 0.13 U = 0.13 U = 0.13 U = 0.13 U = 0.13
Openings [4] U = 1.5 U = 1.5 U = 1.5 U = 1.5 U = 1.5
Allowance for thermal bridging [5] 0.08 x total exposed surface area 0.08 x total exposed surface area 0.08 x total exposed surface area 0.08 x total exposed surface area 0.08 x total exposed surface area
Open flues None One One None One
Heating system (pump in heated space) [10] Gas boiler room sealed fan flued, 90.2% efficiency LPG boiler room sealed fan flued, 90.2% efficiency Oil boiler room sealed fan flued, 93% efficiency Air to water heat pump [6] Wood pellet boiler HETAS approved
Heating system controls Programmer +room thermostat +TRVs +Boiler interlock +weather compensation+delayed start Programmer +room thermostat +TRVs +Boiler interlock +weather compensation +delayed start Programmer +room thermostat +TRVs +Boiler interlock +weather compensation +delayed start Programmer +room thermostat Programmer +room thermostat +TRVs +weather compensation + delayed start
Hot water (HW) system Stored HW (from boiler) separate time control for space and water heating Stored HW (from boiler) separate time control for space and water heating Stored HW (from boiler) separate time control for space and water heating Stored HW by electric immersion Stored HW (from boiler) separate time control for space and water heating
Secondary space heating none 10% closed wood log-burning room heater [7] 10% closed wood log-burning room heater [7] 10% electric none
Solar thermal system Yes [8] Yes [8] Yes [8] Yes [8] Yes [8]


Table 6.2. For the 'notional dwelling' in addition all of the following applies in every fuel type

Windows, doors and rooflights area 25% of total floor area [9]
Orientation all glazing orientated east/west
Shading average overshading
Number of sheltered sides 2
Chimneys none
Ventilation system natural ventilation with intermittent extract fans. 4 for dwellings with floor area more than 80 m2, 3 for smaller dwellings
Air infiltration through building fabric 7m3/m2h at 50 Pa
Hot water cylinder (combined cylinder with 75 litre solar store) 150 litre cylinder insulated with 50mm of factory applied foam (cylinder in heated space); cylinder temperature controlled by thermostat
Primary water heating losses (where applicable) primary pipework insulated
Low energy light fittings 100% of fixed outlets
Thermal mass parameter The value identified for the proposed building should be used
Party wall heat loss (applicable to cavity separating walls) 0.2 W/m2K


Notes:

  1. Where a multi-fuel appliance is proposed, assessment of both TER and DER should be based upon the fuel option with the highest carbon factor (e.g. multi-fuel stove capable of burning coal or wood is assessed as solid mineral fuel). Where heat is supplied to a dwelling from more than one source, through a generation mix (e.g. community heating using both oil and biomass where heat is provided from both sources simultaneously), the primary heating element within the TER should be calculated pro rata, on the basis on the basis of the identified fuel mix. The same mix should be used in calculation of the DER, including any pro rata contribution made by solutions such as CHP. This does not apply where heat demand can be provided solely from one of the identified generating sources, in which case other identified heat sources should be considered as back-up systems and excluded from the assessment.

  2. Where solid mineral fuel is proposed for the main space heating system, the TER should be calculated using the values identified for oil as a fuel (package 3). This will require improvements in performance within the DER specification for compliance.

  3. The biomass column should be used not only where biomass fuel is to be used but also for biogas, large scale waste combustion from boilers and waste heat from power stations.

  4. U is the average U-value of all openings (windows, doors, rooflights) based on one opaque door 1.85 m2 of U =1.5, any other doors fully glazed. For windows, doors etc a frame factor of 0.7, light transmittance of 0.80 and solar energy transmittance of 0.63 are assumed.

  5. For the purposes of setting the TER, a y-value of 0.08 is identified, which assumes construction using the principles set out in the BSD document ‘Accredited Construction Details (Scotland) 2010' (http://www.scotland.gov.uk/topics/built-environment/building/building-standards). In determining the DER, guidance on designing to limit heat loss from non-repeating thermal bridges is given in clause 6.2.3.

  6. For calculation of the TER, radiators should be identified as the distribution system (seasonal performance factor 1.75).

  7. The closed wood log-burning room heater should be capable of burning wood only, not multi-fuel.

  8. Evacuated tube (collector efficiency ηο= 0.6, heat loss coefficient a1 = 3), oriented between SE and SW, pitch not more than 45º from horizontal, solar powered circulation pump. Panel size for TER calculation, rounded to the nearest 0.1 m2, determined as follows:

    Dwelling area < 100m2 : 0.75 + (0.0375 x total floor area)

    Dwelling area > 100m2 : 4.3 + (0.002 x total floor area)

    For dwellings smaller than 35m2, a panel size of 2m2 should be used in the TER calculation.

  9. If total exposed facade area is less than 25% of the floor area, the area of windows, doors and roofs should be taken as the area of the total exposed facade area.

  10. For gas and oil, boiler efficiency values for the specific notional dwelling are SEDBUK (2005). Equivalent values for SEDBUK (2009) are Natural gas and LPG-89%, oil-90%.

6.1.3 Calculating carbon dioxide emissions for the proposed dwelling

The second calculation involves establishing the carbon dioxide emissions for the proposed dwelling (DER). To do this the values proposed for the dwelling should be used in the methodology i.e. the U-values, air infiltration, heating system, etc.

The exceptions to entering the dwelling specific values are:

  1. it may be assumed that all glazing is orientated east/west

  2. average overshading may be assumed if not known. 'Very little' shading should not be entered

  3. 2 sheltered sides should be assumed if not known. More than 2 sheltered sides should not be entered

  4. where secondary heating is proposed, if a chimney or flue is present but no appliance installed the worst case should be assumed i.e. a decorative fuel-effect gas appliance with 20% efficiency as secondary heating. If there is no gas point, an open fire with 37% efficiency should be assumed as secondary heating burning solid mineral fuel for dwellings outwith a smokeless zone and smokeless solid mineral fuel for those that are within such a zone.

All other values can be varied, but before entering values into the methodology, reference should be made to:

  • the back-stop U-values identified in guidance to Standard 6.2 and

  • guidance on systems and equipment within Standards 6.3 to 6.6.

6.1.4 Buildings with multiple dwellings

Where a building contains more than one dwelling (such as a block of flats or terrace of houses) the average carbon dioxide emissions for the proposed block or terrace (DER) may be compared to the average target CO2 emissions (TER) for the ‘notional block or terrace'.

The average emissions for the block or terrace is the floor-area-weighted average for all the individual dwelling emissions, i.e:

{(emissions1 x floor area1)+(emissions2 x floor area2)+(emissions3 x floor area3)+…..)} ÷ {(floor area1+ floor area2 + floor area3) + …..}.

The degree of flexibility which is provided by averaging out building emissions should be used carefully. It is not intended that one or more dwellings are super-insulated (in a building consisting of dwellings) so that another may be constructed with a high percentage of glazing.

6.1.5 Common areas in buildings with multiple dwellings

Communal rooms or other areas in blocks of dwellings (which are exclusively associated with the dwellings) should be assessed either by:

  1. using the guidance to Standard 6.1 for non-domestic building or

  2. ensuring that the glazing does not exceed 25% of the total communal floor area of the building; and the U–values, thermal bridging, air infiltration values equal or better those given for the gas 'notional dwelling' (package 1 in the table to clause 6.1.2).

However where the common areas are less than 50m2 in total these rooms or areas may be treated as a stand-alone building and are not therefore subject to Standard 6.1.

6.1.6 A simplified approach

Where a dwelling is designed to one of the packages of measures in the table to clause 6.1.2, it can be considered to reduce carbon dioxide emissions to the same level as by use of the methodology, calculating and comparing DER with TER.

In using a package of measures east/west orientation, average overshading and 2 sheltered sides may be assumed for the proposed dwelling.

The simplified approach may still be used where there are minor deviations of input values that will clearly achieve the same or a better level of emissions. For example:

  • a thermal mass parameter value of 'medium' should be assumed

  • a boiler with a higher SEDBUK efficiency

  • a ground source heat pump instead of an air source heat pump

  • where secondary heating forms part of the TER calculation, a secondary space heating system of equal or better performance (e.g. a closed, biomass-burning room heater)

  • area of openings between 20% and 25% of total floor area (windows, doors, rooflights, and roof windows)

  • a declared air infiltration of 7m3/m2.h at 50Pa or lower

  • a hot water cylinder with a declared heat loss figure (BS 1566-1: 2002) not exceeding 2.11kWh/day.

This simplified approach should not be used where there is any deviation from values in the table which will result in higher CO2 emissions. An example is if the dwelling has more than 4 extract fans or windows of a poorer U-value. Likewise, if some elements offer poorer performance and others offer higher performance, the simplified approach should not be used.

This approach should also not be used where there is a likelihood of high internal temperature in hot weather or where air-conditioning is proposed. Reference should be made to the guidance to Standard 6.6.

Note that an Energy Performance Certificate (EPC) will still be required, on completion of the dwelling, to meet Standard 6.9.

6.1.7 Conservatories and stand-alone buildings

Conservatories of less than 50m2 in area are stand-alone buildings, thermally separated from the dwelling. A dwelling to which one is attached should be assessed as if there was no conservatory proposed.

For conservatories and other ancillary stand-alone buildings of 50m2 or more the guidance and methodology for non-domestic buildings should be followed.