Find a range of resources about Part L Building Regulation compliance for dwellings.

Part L of the Building Regulations - Dwellings

Part L of the Building Regulations sets out requirements in relation to the conservation of fuel and energy. Part L was updated in 2019 to include the Energy Performance in Buildings Directive (EPBD) requirement for Nearly Zero Energy Buildings.

The definition for Nearly Zero Energy Buildings in the EPBD is:

"a very high energy performance, as determined in accordance with Annex 1. 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".

In line with the EPBD directive, a cost-optimal analysis was carried out to define NZEB requirements. Part L of the Building Regulations defines the requirements in legislation and DEAP demonstrates compliance with the nearly zero energy performance requirements.

Technical Guidance Document Part L (Dwellings)

Guidance and tools

Cost-optimal study

A cost-optimal study is required under the EPBD to define the energy performance required for new buildings and major renovations. The study accounts for the capital, operational, maintenance and carbon costs of various energy efficient solutions and renewable technologies.

Further information

For more detailed information read Cost Optimal Residential Report Ireland 2018 Cost Optimal Residential Report Ireland 2018.

New dwelling NZEB requirement

For new dwellings, NZEB is equivalent to a 25% improvement on the 2011 Building Regulations. It requires the following as calculated in DEAP:

  • Maximum Permitted Energy Performance Coefficient (MPEPC) of 0.3
  • Maximum Carbon Performance Coefficient (MPCPC) of 0.35
  • Renewable Energy Ratio (RER) of 20%

These requirements are set out in the Technical Guidance Document supporting Part L of the Building Regulations.

You can find worked NZEB examples in these Excel versions of the DEAP software. They are from Appendix E of the Technical Guidance Document Part L.

Existing dwelling major renovation requirement

When 25% or more of a building's envelope surface is renovated, Part L regulations require the building's energy performance be upgraded to the cost-optimal level. This is as far as it is technically, functionally and economically possible.

The cost-optimal level is defined as either:

  • a primary energy performance of less than 125 kWh/m2/yr (B2 BER) when calculated using DEAP
  • an upgrade of the ceiling insulation and heating system

Types of renovation work

The major renovation requirement is activated when renovation work affects more than 25% of the surface area of the dwelling. This work typically includes:

  • External wall, external or internal insulation
  • External wall and window
  • External wall and roof
  • External wall and floor
  • New extension

2021 Updates to Building Regulation Part L

The Energy Performance of Buildings Regulations 2021 (S.I. 393 of 2021) came into effect on 27th July 2021. The main provisions of these regulations are:

  • Electric Vehicle (EV) Recharging Infrastructure for new buildings and buildings undergoing Major Renovation with more than 10 parking spaces.
  • Building Automation and Control Systems (BACs) and EV Recharging Points (for buildings with more than 20 car parking spaces), for existing non-residential buildings by 2025.
  • Self-regulating devices in new buildings, and in existing buildings when heat generators are replaced.

DEAP calculations

In relation to the DEAP calculations, the provision of the infrastructure, as outlined above, has no effect on the MPEPC, MPCPC or RER. TGD L 2019 provisions still apply, therefore the MPEPC, MPCPC and RER calculations and results for TGD Part L 2019 in DEAP 4 are also applicable to the TGD L 2021 and 2022. 

A separate TGD Part L 2021 and 2022 option may be made available to assessors in a future update of the DEAP software.

Further information

For more detailed information on Part L compliance visit the Department of Housing, Planning and Local Government website.

Overheating risk in dwellings

SEAI commissioned a study to assess overheating risk in dwellings using CIBSE TM59 methodology. The study also reviewed the available risk assessment tools to avoid or minimise cooling being retrofitted into homes. A range of typical dwellings with different fabric specifications and mitigation measures were modelled for the study.

Energy performance of buildings standards

Annex 1 of the Energy Performance of Buildings Directive outlines requirements for determining energy performance of buildings and methodologies.

In Ireland, the national calculation methodology required by the EPBD is described following the annexes of these overarching standards which are available from National Standards Authority of Ireland (NSAI).

  • I.S. EN ISO 52000-1:2017
  • I.S. EN ISO 52003-1:2017
  • I.S. EN ISO 52010-1:2017
  • I.S. EN ISO 52016-1:2017
  • I.S. EN ISO 52018-1:2017
Ireland National Calculation Methodology Annex A for Dwellings

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