FABRIC ENERGY EFFICIENCY FOR PART L 2013

Transcription

1 Informing the Part L 2013 consultation FABRIC ENERGY EFFICIENCY FOR PART L 2013 WORKED EXAMPLES AND FABRIC SPECIFICATIONS February 2012

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3 Introduction This report has been produced by the Zero Carbon Hub and AECOM in support of the 2012 Building Regulations Part L consultation package. The consultation proposals for Part L 2013 standards relating to new homes include the recommendation that they should comply with a mandatory minimum fabric performance standard (Target Energy Efficiency, TFEE) in addition to the mandatory carbon emissions standard (Target CO 2 Emission Rate, TER). This is a change from the current requirements, where the Approved Document includes a set of elemental backstops for the building fabric as guidance only. The consultation proposes that the minimum fabric performance standard should be based on the methodology of the Fabric Energy Efficiency Standard as put forward by a Zero Carbon Hub Task Group in 2009 and subsequently adopted for Ene2 of the Code for Sustainable Homes (CSH) in November The consultation gives two possible levels at which to set the fabric standard, referred to as Interim FEE and Full FEES. No preference is expressed as to which standard should be set. The specifics of these levels and the Fabric Energy Efficiency (FEE) methodology as a whole are discussed later in this document, as is the interaction between the possible fabric standards and the preferred CO 2 emissions standard for The FEE is a performance standard and hence the specification required to meet any particular level will vary depending on the design of a particular dwelling type. To aid consideration and responses by consultees to the Part L 2013 proposals, this report gives example specifications for four illustrative dwelling types in achieving the Interim FEE and Full FEES levels. The 2012 Part L consultation documents are available from publications/planningandbuilding/brconsultationsection2, and the consultation for new homes is open until 27 th April Terms used in this guide FEE FEES DFEE TFEE Fabric Energy Efficiency Fabric Energy Efficiency Standard Dwelling Fabric Energy Efficiency Target Fabric Energy Efficiency 1

4 The Fabric Energy Efficiency Standard The Fabric Energy Efficiency Standard (FEES) was first developed specifically in response to developing a strategy for the 2016 zero carbon homes requirement by a Task Group led by the Zero Carbon Hub in Subsequently the Fabric Energy Efficiency methodology was adopted within the Code for Sustainable Homes (November 2010 version) section Ene2, with up to 9 credits available for achievement of a range of specific fabric performance levels. The Fabric Energy Efficiency methodology considers the space heating and cooling demand of a dwelling and the FEE achieved (the DFEE 1 ) is affected by: Building fabric U-values; Thermal bridging; Air permeability; Thermal mass; Features which affect lighting and solar gains. The FEE is measured in kwh/m²/yr, and is not influenced by building services, for example heating system, fixed lighting or ventilation strategy. It is a performance standard, meaning that different combinations of fabric specification can be used to reach a particular level. This allows flexibility when developing a fabric specification. Interaction of fabric and CO 2 standards in Part L 2013 Achievement of the fabric standard is independent of the services strategy to provide space and water heating and space cooling (if any) to a dwelling. Alongside a minimum fabric energy efficiency standard, the Part L consultation proposes as the preferred approach, a 2013 CO 2 emissions target (TER) which gives, on aggregate, around 8% reduction from 2010 regulations. This 2013 TER is defined by a concurrent notional building of the same size and shape as the actual building, but which achieves Full FEES by its fabric specification and has gas-based efficient services applied. This CO 2 target can then be met by the actual building by any means available, noting that the minimum fabric performance standard will still have to be met. The ventilation strategy will have to comply with the relevant version of Building Regulations for Ventilation (ADF2010). If the Full FEES target is chosen as the minimum fabric standard for 2013, then dwelling designs intending to use gas boilers would comply with the CO 2 standard with the application of 'efficient services' as per the concurrent notional building, described in Chapter 5 of the technical consultation document 2. If the Interim FEE target is chosen as the minimum fabric standard for 2013, then the proposed CO 2 emissions target will not automatically be met by the addition of gas-based efficient services. In this case the TER can be met by: further improvements in the fabric performance; even more efficient services; the use of low and zero carbon technologies; or a combination of these. Target Fabric Energy Efficiency for Part L 2013 The Part L 2013 consultation refers to two possible levels at which to set the minimum fabric energy efficiency, referred to in the regulations as the Target Fabric Energy Efficiency, or TFEE: Interim FEE, equivalent of achieving five Ene2 credits. In this case, TFEE would be set at: 43 kwh/m²/yr for apartment blocks and mid-terrace houses 52 kwh/m²/yr for end-terrace, semi-detached and detached houses Full FEES, equivalent to achieving seven Ene2 credits. In this case, TFEE would be set at: 39 kwh/m²/yr for apartment blocks and mid-terrace houses 46 kwh/m²/yr for end-terrace, semi-detached and detached houses Full FEES is the standard which a task group led by the Zero Carbon Hub recommended as the minimum requirement for zero carbon homes. 1 Dwelling Fabric Energy Efficiency 2 Chapter 5, Table 1 (page 87), Section 2 Part L: Proposed changes to technical guidance, gov.uk/documents/planningandbuilding/pdf/ pdf 2

5 Calculation methodology The full procedure for calculating the DFEE is defined in Section 11 of the SAP2012 Specification ( 3. For Part L 2013, it is proposed that UK average weather data should be used for both heating and cooling for the purposes of this calculation 4. Dwelling type classification The TFEE is defined by dwelling type. Many dwelling designs are simple to categorise as either detached, semi-detached/end-terrace, mid-terrace or a unit within an apartment block. Where this is not the case some additional flexibility has been proposed. For mid-terrace houses where there are additional heat loss areas; for example due to inclusion of integral garage, drive-through, or steps and/or staggers in the terrace, allowance could be made for this in the TFEE by way of a sliding scale. For small blocks containing apartments with characteristics similar to detached or semi-detached houses, allowance could be made to apply the higher (less onerous) TFEE value. The calculation method to derive a TFEE where the sliding scale applies is given in the Code for Sustainable Homes Technical Guide 5 and further detailed in a supporting document downloadable from This document also gives additional guidance on dwelling type classification. Buildings containing multiple dwellings Where a building contains multiple dwellings, for Part L 2013 it is proposed that the DFEE and in some cases the TFEE can be averaged in the following way: For apartment blocks: DFEE for the block is the floor-area-weighted average of all the individual DFEEs TFEE is already defined by building type, so no adjustment is necessary For a terrace of houses: DFEE for the terrace is the floor-area-weighted average of all the individual DFEEs TFEE for the terrace is the floor-area-weighted average of all the individual TFEEs (including stepped and/or staggered units if relevant) Note that it is not mandatory to adopt the averaging approach. 3 The procedure for calculating FEE is also defined in Section 11 of SAP2009 Specification ( although this implementation did not specify cooling demand to be calculated using UK average weather data. 4 DCLG, 2012 Consultation on changes to the Building Regulations in England, Section two - Part L, Proposed changes to technical guidance, page 90, paragraph 31 5 November 2010 version, available from techguide.pdf FEE specification scenarios This document is intended as a guide to provide practical example fabric specifications that meet the 2013 target fabric standards proposed in the Part L consultation. Four dwelling types are considered: Detached house Semi-detached/end-terrace house Mid-terrace house 4-Storey apartment block, containing 16 one-bed and 16 two-bed apartments For each dwelling type, two example specifications which meet the Interim FEE target and two example specifications which meet the Full FEES target are provided. The first example in each case maintains air permeability above 5 m³/hr/m²@50pa, and takes the approach of achieving the TFEE via a balanced overall improvement in U-values. The second example in each case also maintains air permeability at around 5 m³/hr/m²@50pa, but sets the wall, floor and roof U-values at the limiting values proposed in the 2012 Part L consultation 6. In this case the specification of other elements are altered in order to achieve the TFEE. It should be noted that these limiting values form part of the consultation and feedback on this aspect is encouraged. The air permeability values were chosen to represent the current typical levels for new build homes. In addition to the dwelling scenarios above, an example of calculating the average TFEE and DFEE for a linear terrace is provided on page 8. The average DFEE calculation for the 4-storey apartment block is also detailed here. Modelling of scenarios All modelling was carried out using SAP2009 (v.9.90), using NHER Plan Assessor v A consultation on SAP2012 (which will, when finalised, be used by Part L 2013) was published on 4 th January 2012 and contains a number of proposed changes to SAP which may affect the FEE calculations. It is expected that the mandatory TFEE values that are being proposed in the 2012 Part L consultation would have to be re-based to take these changes into consideration. At time of writing, a consultation version of SAP2012 was not available and hence the potential impact on the TFEE values or DFEE specifications were not able to be assessed. 6 Proposed limiting values are listed at paragraph 4.22, Section 2 Part L: Proposed changes to technical guidance, 3

6 House type 1: House type 1: detached house Detached house The detached house has four bedrooms and an internal floor area of 118 m 2. Interim FEE (52 kwh/m 2 /yr) Full FEES (46 kwh/m 2 /yr) Example 1 Example 2 Example 1 Example 2 External wall U-value (W/m 2 K) Ground floor U-value (W/m 2 K) m Roof U-value (W/m 2 K) Windows U-value (W/m 2 K) 1.0 (triple glazed) (triple glazed) Doors U-value (W/m 2 K) Air permeability (m 3 /hr/m 50Pa) m 1.13 m 9.18 m 1.05 m 9.08 m 7.45 m 7.83 m Calculated thermal bridging (W/m 2 K) DFEE (kwh/m 2 /yr) m 6.93 m 8.57 m Gross internal area: m 2 Ground floor area: m 2 Roof area: m 2 Zone 1 area: m 2 External wall area: m 2 Opening area: m 2 Average internal heights: Ground floor: 2.40 m First floor: 2.70 m Ground floor plan First floor plan 0.93 m m 8.39 m

7 Interim FEE (52 kwh/m 2 /yr) Full FEES (46 kwh/m 2 /yr) Example 1 Example 2 Example 1 Example 2 External wall U-value (W/m 2 K) Party Wall U-value (W/m 2 K) Ground floor U-value (W/m 2 K) Roof U-value (W/m 2 K) Windows U-value (W/m 2 K) 1.2 Doors U-value (W/m 2 K) Air permeability (m 3 /hr/m 50Pa) Calculated thermal bridging (W/m 2 K) (ACD) DFEE (kwh/m 2 /yr) House type 2: Semi-detached / end-terrace house The semi-detached / end-terrace house has three bedrooms and an internal floor area of 76 m². For examples of averaging across a terrace, please refer to page 8. House type 2: semi-detached house 7.83 m 7.83 m Gross internal area: m 2 Ground floor area: m 2 Roof area: m 2 Zone 1 area: m 2 External wall area: m 2 Party wall area: m 2 Opening area: m 2 Average internal heights: Ground floor: 2.40 m First floor: 2.70 m Ground floor plan First floor plan 5

8 House type 3: Mid-terrace house The mid-terrace house has three bedrooms and an internal floor area of 76 m². For examples of averaging across a terrace, please refer to page 8. Interim FEE (43 kwh/m 2 /yr) Full FEES (39 kwh/m 2 /yr) Example 1 Example 2 Example 1 Example 2 External wall U-value (W/m 2 K) Party Wall U-value (W/m 2 K) Ground floor U-value (W/m 2 K) Roof U-value (W/m 2 K) Windows U-value (W/m 2 K) Doors U-value (W/m 2 K) m 4.05 m 1.05 m Air permeability (m 3 /hr/m 50Pa) Calculated thermal bridging (W/m 2 K) DFEE (kwh/m 2 /yr) House type 3: mid-terrace house 9.18 m 9.08 m 7.45 m 7.83 m 8.39 m 6.93 m Gross internal area: m 2 Ground floor area: m 2 Roof area: m 2 Zone 1 area: m 2 External wall area: m 2 Party wall area: m 2 Opening area: m m 1.9 m 1.13 m Average internal heights: Ground floor: First floor: 2.40 m 2.70 m Ground floor plan First floor plan 6

9 1.13 m 9.18 m 1.05 m 3.2 m 1.9 m Windows U-value (W/m 2 K) Interim FEE (43 kwh/m 2 /yr) Full FEES (39 kwh/m 2 /yr) Example 1 Example 2 Example 1 Example 2 External wall U-value (W/m 2 K) Party Wall U-value (W/m 2 K) Sheltered wall U-value (W/m 2 K) Ground floor U-value (W/m 2 K) Roof U-value (W/m 2 K) House type 4: Apartment block The apartment block comprises of 8 flats per floor, and extends over four storeys (total 32 flats). Each floor has four single aspect one-bedroom flats with an internal area of 43 m² and four 2-bedroom corner flats with a floor area of 67 m². Doors U-value (W/m 2 K) Air permeability (m 3 /hr/m 50Pa) Calculated thermal bridging (W/m 2 K), average for block (ACD) (ACD) DFEE (kwh/m 2 /yr) m 9.08 m 8.39 m One-bed Two-bed 7.45 m Gross internal area: m m 2 Zone 1 area: m m 2 Sheltered wall area: m m 2 External wall area: m m 2 Party wall area: m m 2 Opening area: m m m 6.93 m 0.9 m Average internal heights: Average floor height: 2.40 m 2.40 m One-bed apartment 9.08 m Two-bed apartment 8.39 m House type 4: apartment block 7.45 m 7.83 m 6.93 m 8.57 m 7

10 Worked example: Linear terrace The examples given in this document for mid and end-terrace houses have demonstrated how individual compliance could be achieved for both Interim FEE and Full FEES. However, a proposal has been made as part of the 2012 consultation on Part L to allow averaging of the TFEE and DFEE across a terrace of houses. This approach is similar to the TER and DER averaging method detailed in section 4.6 and 4.14 of ADL1A. The purpose of averaging the TFEE across terraces will be to allow the optimisation of the fabric specification for all the dwelling types that comprise the terrace. Three simple examples are shown to the right, for terrace lengths of 3, 5 and 7 dwellings. These examples utilise the mid and end-terrace houses used in the individual dwelling scenarios earlier in this document, without any steps or staggers. For each case, one example specification is shown for the Interim FEE target and one for the Full FEES target. It can be seen that the specifications that have been applied to demonstrate compliance with the terrace average TFEE are slightly different from those that have been listed for the dwelling types to demonstrate compliance individually. Terrace of 3 Terrace of 5 Terrace of 7 Interim FEE Full FEES Interim FEE Full FEES Interim FEE Full FEES External wall U-value (W/m 2 K) Party Wall U-value (W/m 2 K) Ground floor U-value (W/m 2 K) Roof U-value (W/m 2 K) Windows U-value (W/m 2 K) Doors U-value (W/m 2 K) Air permeability (m 3 /hr/m 50Pa) Calculated thermal bridging (W/m 2 K), average for terrace Terrace DFEE (kwh/m 2 /yr) Terrace TFEE (kwh/m 2 /yr) Worked example: Apartment block For apartment blocks, the FEES methodology envisaged that block averaging of the DFEE would likely take place to share the benefits of mid-floor apartments generally having less heat loss than ground or top-floor apartments. Within any particular target level (e.g. Interim FEE or Full FEES ) this was the basis for assigning the lower value to apartment blocks. The general formula for calculating the block DFEE is: {(DFEE 1 x Floor area 1 ) + (DFEE 2 x Floor area 2 ) + (DFEE 3 x Floor area 3 ) + } {Floor area 1 + Floor area 2 + Floor area 3 + } For the 4-storey block used as an example in this document, we have assumed an identical layout of flats per floor and therefore the DFEE calculation is as follows (the Interim FEE Example 1 values are used in this illustration): Units in block TFA (m 2 ) DFEE (kwh/m 2 /yr) Units x TFA Units x TFA x DFEE Small flat - ground floor Small flat - mid floor Small flat - top floor Large flat - ground floor Large flat - mid floor Large flat - top floor Total Block DFEE = (Units x TFA x DFEE ) / (Units x TFA) = kwh/m 2 /yr 8

11 Modelling assumptions All modelling was undertaken using SAP2009 (v.9.90), using NHER Plan Assessor v The following general assumptions were made: Thermal Mass Parameter (TMP) = Medium Thermal bridging was calculated for each dwelling and four scenarios have been considered for the purpose of the modelling exercise in this document. Thermal bridging calculations were made with the assumed use of accredited construction details (ACD) and for EST enhanced construction details. In addition to this an intermediate value was considered for cases where a combination of accredited and enhanced construction details would be used. A y-value of 0.04 W/m²K (or lower in the case of the detached house) was used in the modelling where necessary, with the assumption that this could be achieved with bespoke junction detailing. These variations have been indicated in the specifications tables. The following assumptions were made regarding glazing specification. The SAP default values relating to emissivity and transmittance (g-value) were used, together with a frame factor of 0.7 : U-value of window Window type Low-e coating 1.6 W/m 2 K Double glazed Hard coat W/m 2 K Double glazed Soft coat 1.2 W/m 2 K Double glazed Soft coat 1.0 W/m 2 K Triple glazed Hard coat 0.8 W/m 2 K Triple glazed Soft coat Dwelling facades with the largest glazing proportion were assumed to be facing East. 9

12 Contact Head Office Zero Carbon Hub NHBC House, Davy Avenue Milton Keynes MK5 8FP T F info@zerocarbonhub.org