Building Regulations — Part L NZEB

The requirements regarding the conservation of fuel and energy in dwellings are laid out in the Technical Guidance Document Part L (TGDL) of the Building Regulations. The ultimate goal of Part L is to achieve carbon neutral dwellings in the near future. The requirements to achieve Part L compliance have changed dramatically over the last number of years and the current Part L 2019 represents a 70% improvement in energy efficiency in comparison to Part L 2005. This ensures that new dwellings comply with the European Union NZEB — Nearly Zero Energy Buildings requirement. Nearly Zero Energy Buildings have a very high level of energy performance. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby. The NZEB requirements for new dwellings equate to a BER A2.

The Dwelling Energy Assessment Procedure (DEAP) is the official Irish methodology for calculating the energy performance and associated carbon dioxide emissions for the provision of space heating, ventilation, water heating and lighting in dwellings. DEAP is also the compliance tool specified in Part L of the Irish Building Regulations. DEAP performs compliance checking calculations for Part L and generates a conformance report summarising the relevant information for the purposes of building control.

The calculation checks that the primary energy consumption associated with the operation of the dwelling and the related CO2 emissions do not exceed the Maximum Permitted Energy Performance Coefficient (MPEPC) and the Maximum Permitted Carbon Performance Coefficient (MPCPC) when compared to a reference dwelling defined in the Building Regulations Part L Technical Guidance Document (TGD L). DEAP also checks minimum individual performance levels for fabric insulation, air permeability, heating system, heating controls and the RER — Renewable Energy Ratio.

It is essential that new dwelling designs, including heating and ventilation systems, are tested in DEAP at the earliest possible stage. This will give the greatest flexibility and choice to the Designer/Homeowner. DEAP can be used throughout the build process to check various options and combinations of systems and facilitate finding the most desirable and cost effective ways to achieve good energy efficiency and Building Regulation compliance. It is also important to note that meeting individual targets like back-stop u-values will not ensure compliance in relation to the whole dwelling performance as measured by MPEPC and associate MPCPC. The use of non-default values for Thermal Bridging, supported with appropriate documentation, is critical in achieving compliance. TGDL 2019 does not specify how targets are to be reached and designers and builders are given discretion in choosing their own approach to achieving the required standard.

The key parameters for achieving Part L 2019 NZEB compliance are:

  • Maximum Permitted Energy Performance Coefficient: 0.30
  • Maximum Permitted Carbon Performance Coefficient: 0.35
  • Renewable Energy Ratio: 0.20

NZEB requires that where major renovations (defined as a renovation where more than 25% of the surface envelope of the building undergoes renovation) are carried out on a building, the building should achieve a cost optimal level of energy performance insofar as is technically, functionally and economically feasible. This cost optimal energy performance level is equivalent to a BER B2.

Reference: Technical Guidance Document Part L 2019