Guide to Building Regulations changes 2010

Transcription

1 T E C H N I C A L PA P E R - N O. 1 0 / 0 2 The authors HUW EVANS has a post-graduate degree in Technical Authorship from Sheffield Hallam University. He has a particular interest in building physics and the energy efficiency of buildings and, in collaboration with JPA Technical Literature Ltd., provides training in Part L of the Building Regulations and the use of software to assess energy performance and produce Energy Performance Certificates. Introduction This guide describes the key changes to Parts F, G, J and L of the Building Regulations being introduced in England and Wales in 2010, with particular reference to energy efficiency. The changes to Part G came into effect in April 2010, whilst the changes to Parts F, J and L are effective from 1 October The guide also takes account of the introduction of the Building Regulations The Building Regulations 2010 The Building Regulations 2010 came into force on 1 October 2010 and replace the Building Regulations 2000, which have been revoked in their entirety. The 2010 Regulations are largely intended to consolidate the requirements of the 2000 Regulations and subsequent amendments. The differences are therefore mainly in numbering and ordering, with the text not substantively amended during consolidation. There is one change to Part L of Schedule 1 of the Regulations, as L1(c) provision of information to building owners has been removed, and is now Regulation 40. Part L - Conservation of fuel and power The changes to Part L are being introduced as part of the government's long-term commitment to reduce carbon dioxide emissions to 80% below1990 levels by In order to achieve that overall target the CO2 levels for new dwellings are set to be to: 25% below 2006 levels by 2010; 44% below 2006 levels by 2013; Zero carbon by The comparable target for new buildings other than dwellings is that they be zero carbon by The 2010 revisions of Part L are designed to give a reduction in emission levels for new buildings of 25% compared to That reduction is being applied equally to all dwellings, but for buildings other than dwellings, where energy use varies significantly between building types, the revisions are designed to produce an aggregate reduction of 25% across all nondwellings. Other changes result from research into the performance of completed buildings and the need to bring design performance and as-built performance closer together. Whilst the consequences for design and construction of those targets are substantial, for the most part the revisions build upon the 2006 changes to Part L: there are still four Approved Documents supporting Part L, and the five compliance criteria for new buildings are unchanged. Procedural changes In addition to the overall reductions in carbon dioxide emissions the revisions introduce several procedural changes: 1 The existing requirement to submit 'as-built' carbon dioxide emissions calculations to the Building Control Body (BCB) on completion of building work has been supplemented by a requirement to submit 'as-designed' emissions calculations before building work begins. The intention is to enable BCBs to identify and monitor the features of the specification which are significant for achieving the design performance: it may also prevent work beginning on noncompliant designs. The current exemption from Part L for conservatories and porches of less than 30 m2 has been modified, and now only applies if the conservatory or porch is not heated by the main heating system, and is thermally separated from the rest of the building. This change is part of a long-

2 Part L - Conservation of fuel and power (cont) term process to remove the exemption completely. The requirement for commissioning has been extended to ensure all fixed building services, including New dwellings - L1A mechanical ventilation systems in dwellings use no more fuel and power than is reasonable. The requirement does not apply if testing and adjustment is not possible, or would have no effect on energy efficiency. 1. Building a greener future, Budget statement, 2008 The criteria for compliance are set out in Approved Document L1A 2010 Conservation of fuel and power in new dwellings. Achieving the TER The principle for compliance with criterion 1 is unchanged: the rate of carbon dioxide emissions from the dwelling (DER) must not exceed the target emission rate (TER) derived from the emissions from a notional building. However, there are significant changes in the calculation process: both the TER and DER are now calculated using SAP 2009 (see SAP 2009, page 3). the carbon dioxide emission factors of fuels have been revised, and are higher for almost all fuels. the TER is reduced by a further 25%. The equation for deriving the TER is now: TER = (C H x FF x EFA H + C L x EFA L ) x (1-0.20) x (1-0.25) where: C H and C L are the carbon dioxide emission for heating and hot water, and lighting respectively, calculated using SAP 2009, but using the SAP 2005 emission factors for mains gas and electricity. FF is the fuel factor, which increases the TER where the main heating fuel has a higher emission rate than mains gas. EFA is the Emissions Factor Adjustment, which allows for the difference between the SAP 2005 and SAP 2009 emission factors for the same fuel (the EFA is calculated for a fuel type by dividing its 2009 emission factor by its 2010 emission factor: fuels with a fuel factor of 1 have the same EFA as mains gas). (1-0.20) is the 20% reduction in emissions introduced in 2006 (1-0.25) is the 25% reduction in emissions required by The DER is calculated for the building as designed, then as built. Secondary heating is included in the DER calculation only if an appliance is installed or there is provision such as a gas supply or a flue: low energy lighting is included in the proportion planned/installed. Table 1 - Limiting U-values for dwellings (area weighted averages) Element 2010 (W/m 2 K) 2006 (W/m 2 K) Roof Wall Party wall 0.20 N/A Floor Windows, doors, rooflights Limiting values The limiting values for building fabric and services have been retained, but generally tightened. U-values: the area weighted U-values have been tightened (see Table 1), although the limit for floors remains unchanged. Complying with the minimum values will not usually enable a dwelling to achieve the TER (Whilst Approved Document L1A no longer sets upper limits for individual elements, Approved Document C still sets maximum U-values for elements in order to prevent surface condensation.) Air permeability: the limit is unchanged at 10 m 3 /m 2.hr. Building services, including mechanical ventilation and air conditioning systems, must meet the minimum efficiency values in Domestic Building Services Compliance Guide. Fixed internal lighting: 75% of units must now be low energy. Summer overheating In order to avoid excessive internal temperatures, solar gain within a dwelling must be limited. The methodology in Appendix P of SAP 2009 must be used to assess the likelihood of overheating during the summer. The calculation is carried out for June, July and August, using regional monthly weather data, together with the thermal mass defined in the SAP calculation. Although space cooling is now incorporated into the SAP calculation the overheating assessment must be carried out without space cooling operating. 2

3 New dwellings - L1A (cont) Quality of construction and commissioning To ensure the performance of the completed dwelling is consistent with the calculated DER the building fabric should have reasonably continuous insulation, and air permeability should be within reasonable limits. Continuity of insulation party walls: Under AD L1A 2006 heat loss through party walls was regarded as negligible and ignored: recent research, in particular that carried out on the Stamford Brook development, has demonstrated that air flow in party cavity walls can result in substantial heat loss. Consequently, party walls must now be included in SAP assessments, but using the U-values shown in Table 2, rather than calculated values. Table 2 - U-values for party walls multiplying the total area of exposed elements by a coefficient y, where y = Air pressure testing: The minimum test sample for air pressure testing for a development is three dwellings of each type (or 50% of the type if that is less); testing should be scheduled so half the tests are carried out on the first 25% of each dwelling. For each tested dwelling the air permeability should not exceed 10 m 3 /m 2.h at 50 Pa, and the DER calculated with the tested air permeability should not exceed the TER. For those dwellings which are not tested the DER should be calculated using the type average air permeability plus two. In order for those untested dwellings to comply, the type average must therefore not exceed 8 m 3 /m 2 /hr. Party wall construction U-value (W/m 2 K) Solid 0.0 Unfilled cavity with no effective edge sealing 0.5 Unfilled cavity with effective edge sealing 0.2 around all exposed edges and in line with insulation layers at abutting elements A fully filled cavity with effective sealing at 0.0 all exposed edges and in line with insulation layers in abutting elements As the lower U-values require cavities to be sealed and/or filled there is potentially a conflict with some of the requirements for controlling sound transmission in Approved Document E. Continuity of insulation junctions: The heat loss at junctions between building elements and at openings must be assessed by using measured junction lengths and appropriate values for linear thermal transmittance (psi-values) in the DER calculation. Psi-values given for accredited construction details may be used as given, while calculated values must be increased by the greatest of 0.2 or 25% because they have not been assessed for buildability and site quality. In the absence of valid psi-values the heat loss is calculated by If a dwelling fails the pressure test then remedial work must be carried out and the dwelling re-tested: the test sample is also increased by one, and remedial measures should be carried out to untested dwellings of the same type. Testing can be avoided on developments of one or two dwellings by using an air permeability of 15 m 3 /m 2.hr in the DER calculation: compensating measures will then be required to achieve the TER. Commissioning: Fixed building services, including air cooling and ventilation systems must be commissioned, provided their efficiency could be improved by testing and adjustment. Commissioning should follow the procedures in the Domestic 3 building services compliance guide and the Domestic Ventilation Systems Compliance Guide. Provision of information Where paragraph L1 imposes a requirement the person carrying out the work must, within five days of completion of the work, provide the building owner with sufficient information about the building, its fixed services and their maintenance requirements to enable the building to be operated reasonably efficiently. This requirement is now in Regulation 40 and not in Part L. SAP 2009 SAP 2009 (version 9.90) represents a comprehensive overhaul of the Standard Assessment Procedure, with substantial changes in the calculation methodology, including: the use of monthly data for factors such as wind speed, air infiltration, hot water heating losses, solar thermal, solar gain and space heating. the assumption of an intermittent heating pattern (2 + 7 hours of heating on weekdays with 16 hours at weekends) when assessing the space heating requirement. explicit calculation of the thermal mass of the building fabric; the data is used determine the amount of energy required to bring the dwelling up to temperature, and the rate at which it cools between heating periods. As part of the thermal mass calculation, SAP assessors must measure the surface areas of internal walls, floors and ceilings, and calculate the heat capacity (k-value) of both external and internal elements. In addition, party walls must now be included in the SAP calculation as heat loss elements, with U- values taken from the standard values in Approved Document L1A (see table 2). The changes in the treatment of heat loss at junctions (see Quality of construction and commissioning) means the aggregate method of calculating Htb will only be accepted for dwellings without calculated psi-values. In order to avoid the high levels of heat loss produced by that method SAP assessors will have to measure junction lengths and enter them together with the appropriate psivalues.

4 New buildings other than dwellings - L1B The criteria for compliance are set out in Approved Document L2A 2010 Conservation of fuel and power in new buildings other than dwellings. Carbon dioxide emission rates The principle for compliance with criterion 1 is unchanged: the rate of carbon dioxide emissions from the building (BER) must not exceed the target emission rate (TER) derived from the emissions from a notional building. However, the methodology for calculating the TER has changed and there are no longer improvement factors or LZC (low and zero carbon technologies) factor. The TER is calculated using either version 4 of the government's free issue isbem software or approved dynamic modelling software. The TER is derived from the emissions from a notional building which has the same form as the actual building; the demand for heating, lighting and hot water being based on the activity type specified for each zone of the actual building. The methodology distinguishes between buildings which are largely side lit by vertical windows and those lit by a substantial proportion of roof windows. The specifications for the proportion and type of glazing and the efficiency of fixed building services within the notional building therefore vary according to whether the actual building is side-lit or top lit. The TER is then the carbon dioxide emissions per m 2 of floor area from the notional building. Limiting values The limiting values for building fabric and services have been retained and slightly tightened: U-values: The area weighted values are unchanged, except for those for high usage entrance doors and roof ventilators which have been reduced from 6 W/m 2 K to 3.5 W/m 2 K (Table 3). (Upper limits for individual elements are set in Approved Document C in order to prevent surface condensation). Air permeability: the limit is unchanged at 10 m 3 /m 2.hr. Building services must meet the minimum efficiency values in the Non-domestic Building Services Compliance Guide. Table 3 - Limiting U-values for buildings other than dwellings (area weighted averages) Element U-value (W/m 2 K) Roof 0.25 Wall 0.35 Floor 0.25 Windows, roof windows, rooflights, 2.20 pedestrian doors, curtain walling Vehicle access and similar large doors 1.50 High-usage entrance doors 3.50* Roof ventilators including smoke vents 3.50* * 6.0 W/m 2 K in AD L2A 2006 Table 4 - Reference glazing systems Overheating Solar gain during the summer must be limited, to reduce either need for air conditioning or its installed capacity. For each space which is occupied (by the same person for a substantial part of day) or mechanically cooled, the aggregated solar gains for April- September should be no worse than those predicted for the appropriate reference system (table 4). Designers should be aware that meeting the overheating criterion for a naturally ventilated building does not guarantee satisfactory internal conditions. Condition Side lit any height Top lit 6 m high Top lit > 6 m high Glazed element East facing façade Horizontal roof Horizontal roof Area of glazing 1 m x full width 10% viewed from 20% viewed from inside inside Framing factor 10% 25% 15% g-value (normal solar energy transmittance) 4

5 New buildings other than dwellings - L1B Quality of construction and commissioning The performance of the building as constructed and equipped should be consistent with the calculated BER. Building fabric: Insulation should be reasonably continuous with no reasonably avoidable gaps at junctions between elements and at openings. The BER calculation may be conducted with linear thermal transmittances (psivalues) derived from: quality-assured accredited construction details: psi-values may used without modification; calculation by a qualified person: psivalues should be increased by 25% or 0.02, whichever gives the greatest increase. unaccredited details with no quantification of heat loss: psi-values should be the generic values in BRE Information Paper IP 1/06 increased by 50% or 0.4, whichever gives the greatest increase. Air pressure testing: The standard is unchanged from 2006: on testing, a building must achieve an air an permeability no greater than 10 m 3 /m 2.h and the BER calculated with the measured air permeability must not exceed the TER. Remedial work and retesting is required if the result is greater than 10 m 3 /m 2.hr, but other improvements may be adopted to achieve the TER. Testing can be avoided on buildings with useful floor area of less than 500 m 2, by using an air permeability of 15 m 3 /m 2.hr in the BER calculation: compensating measures will then be required to achieve the TER. Table 5 - Ductwork pressure classes Commissioning: Building services must be commissioned in accordance with CIBSE Commissioning Code M: Commissioning management. Ductwork leakage testing: Ductwork should be tested for leakage in accordance with DW/143 3 if: it is served by fans with a design flow rate greater than 1 m 3 /s; DW/143 recommends testing for the pressure class; the BER calculation assumes a better leakage rate than the standard for that particular class. Ductwork should satisfy the leakage limits in table 5, otherwise remedial work and re-testing will be necessary. Pressure class Design static pressure (Pa) Maximum Air leakage air velocity (m/s) limit (l/(s.m 2 ) of duct surface area) Maximum Maximum positive negative Low pressure rp 0.65 (class A) Medium rp 0.65 pressure (class B) High pressure rp 0.65 (class C) 3. DW/143 A practical guide to ductwork leakage testing. HVCA CIBSE TM 31 Building log book tool kit Provision of information Building owners should be provided with sufficient information to enable the fixed building services to be operated efficiently, for example, by providing a log book which follows CIBSE TM Special cases Modular and portable buildings: The placing of an existing module on a new site is treated as the construction of a new building. In such cases the TER can be adjusted to allow for modules which were built to comply with earlier versions of the Approved Documents to Part L. The requirements are further relaxed for portable buildings with a planned life of less than two years Shell and fit-out: Buildings intended for sale or letting for subsequent fit-out work should have the design stage TER/BER submission based on the proposed shell and a set of assumed efficiencies for services. At practical completion the TER/BER should be based on the building and systems actually constructed. The fit-out work also requires TER/BER calculations, which should be based on the shell as constructed and the installed services. 5

6 Existing buildings The guidance on existing buildings is given in AD L1B 2010 Conservation of fuel and power in existing dwellings and AD L2B 2010 Conservation of fuel and power in existing buildings other than dwellings. The compliance methods are similar for both types of building and address: extensions; material changes of use; change of energy status, where building work results in a previously exempt building losing its exemption (e.g. by the provision of heating); consequential improvements. The guidance also applies to refurbishment work to modular buildings and subsequent fit-out work in shell and core buildings. Extensions Extensions can comply by three methods: an elemental method: thermal elements should comply with table 8, and the proportion of openings should not exceed that in table 6; an area weighed U-value method: the area weighted U-value of all elements should be no greater than that of a extension of the same size and shape which complies by the elemental method; a whole building method: an appropriate calculation tool may be used to demonstrate that carbon dioxide emissions from the building with the proposed extension do not exceed those for the building plus a notional extension which complies with the elemental method. In all cases, the fixed building services should comply with the domestic or non-domestic building services compliance guide. Large extensions to buildings other than dwellings should be treated as a new building under Approved Document L2A if its total useful floor area: exceeds 100 m 2 ; and it is greater than 25% of the total useful floor area of the building. Table 6 - Opening areas in extensions Building type Windows and Rooflights as % personnel doors of roof area as % of exposed wall Residential Places of assembly, offices, shops Industrial and storage Vehicle access doors As required Not applicable Smoke vents Not applicable As required Material change of use and change of energy status Where a building undergoes a material change of use or undergoes a change of energy status, thermal elements, controlled fittings and controlled services should comply with the requirements below. Where the area of openings would be more than 25% of floor area, that area should either be reduced or compensating measures taken, based on comparative carbon dioxide emissions calculations. 6

7 Existing buildings (cont) Table 7 - Maximum U-values for new and replacement thermal elements Element U-value (W/m 2 K) Wall 0.28 Pitched roof insulation at ceiling level 0.16 Pitched roof insulation at rafter line 0.18 Flat roof or roof with integral insulation 0.18 Floor 0.22 Swimming pool basin 0.25 Table8 - U-values for refurbishing and upgrading thermal elements Element (a) Threshold U-value (b) Improved U-value (W/m 2 K) (W/m 2 K) Wall - cavity insulation Wall - external or internal insulation Floor Pitched roof - insulation at ceiling level Pitched roof - insulation at rafter line Flat roof or roof with integral insulation Table 9 - Standards for controlled fittings Building type Fitting Standard Dwelling Window, roof window, WER* = Band C, or rooflight U-value 1.6 W/m 2 K Doors U-value 1.8 W/m 2 K Other buildings Windows, roof windows Centre pane U-value and glazed rooflights 1.5 W/m 2 K Whole unit U-value 1.2 W/m 2 K Windows in domestic buildings WER* = Band B or C (e.g. student accommodation, care homes) Plastic rooflight U-value 1.8 W/m 2 K Pedestrian doors > 50% Whole unit U-value internal face glazed 1.8 W/m 2 K High usage entrance doors U-value 3.6 W/m 2 K for people Vehicle access and similar U-value 1.5 W/m 2 K large doors Other doors U-value 1.8 W/m 2 K Roof ventilators (including U-value < 3.5 W/m 2 K smoke extract) *Window Energy Rating 7 Thermal elements Thermal elements comprise floors, walls and roofs which separate the interior of the building from outside, from unconditioned spaces or from spaces conditioned to a different heating pattern. New and replacement thermal elements should comply with table 7, while renovated thermal elements should be improved to comply with column (b) of table 8. An existing elements may need to be upgraded if: it is an existing thermal element in a building subject to material change of use; it becomes a thermal element where previously it was not; it is an existing element being upgraded as a consequential improvement. If the performance of the element is worse than column (a) of table 8 it should be upgraded to comply with column (b), provided that is technically, functionally and economically feasible (judged on a simple pay back of 15 years). Lesser provision may be acceptable for thermal elements where meeting the standards could result in the loss of more than 5% of floor area, or there would be significant problems in adjoining floor levels. Controlled fittings and services Controlled fittings, such as windows and doors should meet the performance standards in table 9. Controlled services should meet the minimum standards in the the appropriate domestic or non-domestic compliance guide

8 Quality of construction and commissioning Consequential improvements Building work to a non-dwelling with a floor area greater than 1,000 m 2 can trigger a requirement to make improvements to other parts of the building. Such consequential improvements will be required where the work includes: an extension; initial provision of a fixed building service; an increase in the installed capacity of a fixed building service. The guidance for consequential improvements is broadly the same as AD L2B There remains a cost limit on improvements of 10% of the value of the principal works when a building is extended: there is no such limit on improvements consequent on changes. Part F - Ventilation The ventilation levels set in earlier editions of Approved Document F relied to some extent upon 'adventitious ventilation' resulting from air leakage through the fabric. As the 2006 changes to Part L reduced the amount of air leakage there was a risk that buildings with air permeabilities of 5 m 3 /m 2.hr and lower would be insufficiently ventilated. Also, recent research has shown that the installed performance of mechanical ventilation systems is often well below their design performance. The 2010 revisions are designed to address both those concerns. Ventilation in dwellings The major change in the guidance has been to set alternative ventilation rates for dwellings with as-built air permeabilities greater than 3 m 3 /m 2.hr. It is recommended that the lower ventilation rates only be used if the design air permeability is greater than 5 m 3 /m 2.hr and the person carrying out the work has previous experience of closely matching design with as-built air permeability levels. Procedural changes There are a number of procedural changes associated with Part F: Commissioning: mechanical ventilation systems in dwellings must now be commissioned to ensure they operated efficiently; Testing: the air flow rate of mechanical ventilation systems in new dwellings must be tested and the result reported to the BCB. Information: building owners must now be provided with information to enable them to maintain mechanical ventilation systems and operate them efficiently. Approved Document F is now supplemented by the Domestic Ventilation Compliance Guide. Part J Fuel burning appliances The rates of ventilation for fuel burning appliances set in previous editions of Approved Document J presumed that adventitious ventilation' (air leakage through the fabric) provided some of the combustion air. The reduction in air leakage rates following the introduction of air permeability standards and pressure testing has required a review of ventilation provision to ensure fuel burning appliances have sufficient air supply. The guidance in Approved Document J 2010 is, for the most part, the same as that in the 2002 edition; however, the ventilation requirements for fuel burning appliances have been revised: in most cases the rate of ventilation per rated kw has been retained, but the lower limit of application has been removed (for example, in cases where Approved Document J 2002 required openings of 500 mm 2 per rated kw input in excess of 7 kw, Approved Document J 2010 retains the rate of 500 mm 2 /kw, but requires it for every rated kw). 8 There is also a new requirement, J3, to fit carbon monoxide detectors when new solid fuel appliances are installed: the existing requirements J3 J6 have been renumbered in the Building Regulations 2010 to run from J4 J7. Part G Water efficiency Part G Sanitation, hot water safety and water efficiency has been substantially revised in Whilst most of thee changes address health and safety concerns, a new requirement G2 (Water efficiency) addresses sustainability and water consumption. Fittings and appliances must now use water efficiently, and under the new Regulation 36, the predicted consumption of wholesome (potable) water for a new dwelling must not exceed 125 litres/person/day. The calculation uses the same methodology as the Code for Sustainable Homes, but with an additional allowance of 5 litres/person/day for activities such as washing cars and watering plants. As the calculation measures wholesome water usage, not on total water usage, there are two methods by which the required performance may be achieved: reducing overall water consumption by specifying and installing fittings with lower flow rates; reducing wholesome water consumption by using harvested rainwater or reclaimed 'greywater' for those functions which do not require wholesome water (such as washing clothes or flushing toilets). A lower rate of water usage results in less energy being required to provide domestic hot water, which is reflected in a 5% reduction in calculated hot water usage within SAP for a dwelling with a total water consumption of less than 125 l/person/day.

9 Glossary Disclaimer Air permeability: the rate of air infiltration through a building's fabric, expressed in m 3 /m 2.hr at a pressure differential of 50 Pa. Building Emission Rate BER: the predicted rate of carbon dioxide emissions from a proposed or completed building (other than a dwelling), expressed in kilograms of CO 2 emitted per square metre of floor area per year (kgco 2 /m 2 ). The BER must be equal to or lower than the building's TER. Consequential improvements: improvements required to the fabric and/or services of existing non-domestic buildings when the building is extended, or building services are provided or their capacity is increased. Dwelling Emission Rate DER: the predicted rate of carbon dioxide emissions from a proposed or completed dwelling, expressed in kilograms of CO 2 emitted per square metre of floor area per year (kgco 2 /m 2 ). The DER must be equal to or lower than the dwelling's TER. Dynamic Simulation Modelling DSM: software which can analyse energy use within buildings taking account of changing environmental conditions and patterns of use. Approved DSM software can be use for TER/BER calculations. Emissions Factor: the amount of greenhouse gases released for each unit of energy produced by a type of fuel, expressed in kgco 2 /kwh. Although the measure is treated as measuring CO 2 the 2010 emission factors include the impact of other greenhouse gases (N 2 O and CH 4 ). Emissions Factor Adjustment EFA: an figure which adjusts the TER for dwellings to allow for the change in carbon dioxide emission rates between 2006 and Fuel factor FF: a figure which adjusts the TER for dwellings in which the main heating fuel for the actual dwelling has a higher emissions rate than mains gas. Htb: for dwellings, the total rate of heat loss occurring through junctions between building elements and around openings. It can be calculated accurately, using psivalues, or estimated within a SAP calculation. isbem: the government's free-issue, data gathering software for carrying out SBEM calculations. Low and Zero Carbon Technologies LZC: renewable systems such as biomass boilers, heat pumps and photovoltaic panels. Notional building; a theoretical building which is used to calculate carbon dioxide emission limits for an actual building. The notional building has the same size and shape as the actual building, but the performance of its fabric and services is specified as part of the National Calculation Methodology. Psi-value: the rate of conduction heat transfer at a junction between building elements and around openings, expressed in W/mK. Simplified Building Energy Model SBEM: the national calculation methodology for assessing energy use and carbon dioxide emissions from buildings other than dwellings. For more complex buildings, such as those with atria, DSM software is required. Standard Assessment Procedure SAP: the approved methodology for assessing energy use and carbon dioxide emissions for dwellings. SAP 2009 (version 9.90) must be used to demonstrate compliance with Part L Target Emission Rate TER: the maximum permitted carbon dioxide emission rate for a proposed or completed building, expressed in kilograms of CO 2 emitted per square metre of floor area per year (kgco 2 /m 2 ). The TER is calculated from the emission rate for a notional building of the same size and shape as the actual building. Thermal element: a wall, roof or floor which separates the building interior from outside, from unconditioned spaces or from spaces conditioned to a different heating pattern. U-value: the rate of conduction heat transfer through a building element, expressed in W/m 2 K. Window Energy Rating WER: A rating system which takes account of a window's U-value, air leakage rate and solar gain. Rating run from A to G, with A being the most efficient. 9 The information provided in this document is offered in good faith and every effort has been made to check its accuracy, however readers should always make their own checks. Neither the author nor JPA Technical Literature Ltd accept any responsibility for misstatements made in it or misunderstandings arising from it. JPA Technical Literature Ltd JPA Technical Literature Ltd provides a wide range of services to the construction industry, including technical documentation and research, thermal calculation software and training. Website: