¶ Compliance with Part L and improving the BER grade
Clients and homeowners can often ask how they can achieve an “A” rating in their new or existing dwelling, or how can they achieve compliance with the latest Energy and CO2 performance requirements in Part L of the Building Regulations. There is no one specification that will guarantee that the “A” rating or Part L compliance is achieved as there are well over 50 parameters that can impact a BER and Part L assessment outcome.
For the purposes of Part L compliance, the calculated Energy Performance Coefficient (EPC) and Carbon Performance Coefficient (CPC) mustn’t exceed the Maximum Permitted Energy Performance Coefficient (MPEPC) and the Maximum Permitted Carbon Performance Coefficient (MPCPC).
In the 2022 Technical Guidance Document (TGD) to Part L, the MPEPC is 0.3, meaning that the dwelling’s calculated energy usage must be no more than 30% of the TGD L Appendix C reference dwelling EPC. Likewise, the dwelling’s calculated CO2 emissions must be no more than 35% (the MPCPC) of the TGD L 2022 Appendix C reference dwelling CPC. These are the values checked in DEAP.
A BER cert may be published for new dwellings regardless of whether the building meets Part L requirements. However, the BER assessor is required to notify their client in writing which elements of the dwelling design do not comply with Part L as calculated in DEAP.
The client or the dwelling designer may ask the BER assessor to help identify dwelling design changes to achieve Part L compliance in DEAP. It is always recommended to perform the DEAP calculation at early design stage prior to commencement as detailed in TGD L. This calculation should be kept under review and take account of changes to specification during construction e.g. heating system efficiency, window solar gain, thermal bridging details, MVHR specification changing after the original DEAP assessment is carried out.
Non-default performance as listed on relevant databases, third party certificates or CE marked literature should be used in preference to DEAP default values. See the guidance in the DEAP manual on “Accredited or certified data” under the “General Principles” section along with references to other relevant data sources and databases in the DEAP manual. For all DEAP entries, bear in mind the DEAP methodology requirements for valid supporting documentary evidence when carrying out a BER.
When seeking to achieve compliance with TGD L for dwellings it is worth reviewing the sample dwellings available from Department of Housing Planning and Local Government (DHPLG):
If still having difficulty identifying why the dwelling is not complying with Part L after reviewing the above sample dwellings, check through the following list to see potential areas for improvement. The following guidance is not exhaustive and is intended to help assessors identify how to achieve compliance by making improvements to the dwelling being assessed in several areas:
Ventilation
- For new dwellings, a permeability test result should be sought for entry in DEAP. For new-provisional ratings a value may be assumed as per Section 5.4 of this document. For new-final ratings, permeability test results are produced in accordance with IS EN 9972:2015 (Supersedes IS EN 13829) by a person certified by an independent third party to carry out this work, e.g. National Standards Authority of Ireland certified or equivalent. Air pressure testing should be carried out on all dwellings on all development sites, as outlined in TGD L Section 1.3.4.4.
- Open flues and chimneys contribute to ventilation heat losses in DEAP. System designers should minimise these losses using balanced or room-sealed flues or permanent dedicated combustion air supplies where possible (whilst adhering to all other relevant sections of Building Regulations e.g. see TGD J).
- Background permanent ventilation for TGD F purposes will have reduced losses where controllable/closable vents are used (whilst adhering to all other relevant sections of Building Regulations). Combustion for Part J Heat Producing Appliances should be provided through permanent ventilation openings
- Non-default values for mechanical ventilation are taken from SAP Appendix Q’s Product Characteristics Database and generally will result in lower calculated energy usage in DEAP than use of defaults.
- The use of heat recovery systems can result in improved performance where non-default MVHR system parameters from SAP Appendix Q‘s Product Characteristics Database are used. Target increased efficiency and minimise Specific Fan Power when recommending a product from the Product Characteristics Database. When using heat recovery systems in your design, air tightness of the building has significant impact on the CPC and EPC results obtained. Aim for higher levels of air tightness. The dwelling design must adhere to all other relevant sections of building regulations.
Building Elements
- While the dwelling must at least meet the minimum requirements in different sections of Part L (e.g. fabric requirements), the dwelling is more likely to achieve MPEPC/MPCPC compliance if the dwelling exceeds the requirements in different sections. For example, a dwelling with a wall U value of 0.12 W/m2K is more likely to meet MPEPC/MPCPC than a dwelling with a wall U-value of 0.18 W/m2K. The construction and depth of an external wall will change depending on the U-Value required, therefore it is important that the planned U-Value is specified in a DEAP calculation prior to commencement. The U-value required in a sloped roof may also influence the roof construction so again this should be specified in DEAP prior to commencement.
- Aim for a thermal bridging factor of 0.08 (from Acceptable Construction Details) or lower. See the Thermal Bridging section of Global Factors.
- Use certified U-values and solar transmittance values for windows. See Windows and Doors section of Building Fabric. Window orientation, glazing areas and locations can be optimised to capitalise on solar gain (e.g. minimise North facing windows and optimise South facing windows).
Water Heating
- Reduce the “temperature factor multiplier” for hot water storage following options in Table 5.1 of the Options and Storage section in Hot water, (e.g. by having time and temperature control for an indirect cylinder).
- Increased cylinder insulation will reduce the losses from the hot water cylinder (particularly factory fitted insulation).
- Minimise the primary circuit losses e.g. if there is a boiler and cylinder, it is better to have all primary pipework between the boiler and cylinder insulated and ensure there is a cylinder thermostat.
- A well-designed solar water heating system typically has a solar fraction of 50-60% - although this will depend on the needs of the client. Source non-default parameters for the solar collectors (e.g. using HARP). Use a cylinder with a larger dedicated solar storage volume to increase the yield from the solar collectors.
Distribution System Losses and Gains
- Aim for a higher control category and lower temperature adjustment by having a high level of heating system controls. For example, a boiler heating system should at least have a programmer and two or more thermostats. TGD L outlines zoning and controls guidance for new dwellings.
- Boiler systems should have boiler interlock to improve the efficiency adjustment factor. See heating controls in the controls and responsiveness section of the Space heating tab.
- Where there are central heating pumps, use pumps with an energy label showing low wattage and high efficiency. See the footnote to table 4.9 entitled “Note on use of non-default central heating pump electricity consumption”.
- Table 4.6, Table 4.8, and controls and responsiveness in Section 4 discuss several other control options that may improve the dwelling’s EPC and CPC (e.g. delayed start thermostats and load/weather compensation).
Energy Requirements
- Source non-default values for space heating (main and secondary) and water heating. Check HARP and other certified sources for appropriately certified data.
- The adjusted space and water heating efficiency can be optimised according to space heating emitter type, operating temperatures, and system parameters, particularly for heat pumps. See Table 4.8 for details.
General
- Follow the DEAP methodology when checking the dwelling design for Part L compliance using DEAP. The dwelling must comply with all relevant facets of Building Regulations.
- Default values are generally conservative. Use non-defaults supported by the appropriate evidence detailed in the DEAP manual and survey guide. For example, check HARP for heating systems, IAB for insulation thermal conductivities and so on. Non-default values in DEAP must always be supported by valid evidence from the correct database, accredited source, test data, etc. See the DEAP manual for guidance
- Investigate incremental improvements such as:
- Minimise fabric and ventilation losses
- Maximise solar, heat and light gains
- Improved air tightness
- Improved insulation levels
- Use better non-default values for HVAC efficiencies, U values etc.
- Optimise heating controls.
- It may be necessary to specify additional renewable systems subject to how the client and dwelling designer plan to achieve compliance.
- Review the DEAP results tab and see which section has the highest demand (e.g. water heating or space heating). Identify improvements to reduce that section as this is likely to yield the most significant improvement to EPC and CPC.
Training courses are available from 3rd parties to assist in achieving Part L compliance. SEAI is not involved in the delivery or development of these training courses
Additional key references and databases: