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Nearly Zero Energy Building (NZEB)

Updated: Feb 19, 2020

‘Nearly Zero Energy Buildings’ means a building that has a very high 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.


Nearly Zero Energy Building (NZEB)

The NZEB standard will apply to all new buildings occupied after the 31st December 2020. For Public Sector bodies, the standard will apply to all new buildings owned and occupied by the 31st December 2018.As with previous Building Regulations there are transitional arrangements in place where buildings are occupied after these dates but work commenced prior to 31st December 2018 for Non Domestic Buidlings and 31st October for Domestic Buildings.


What are Nearly Zero Energy Buildings

The definition for Nearly Zero Energy Buildings in the Energy performance in Buildings Directive (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, Ireland carry out a cost optimal analysis to define NZEB requirements. Part L of the Building Regulations defines the requirements in legislation.


Requirements for Non Domestic Buildings

For new buildings

For all new builds, an equivalent to a 60% improvement in energy performance on the 2008 Building Regulations is required. This means an improved energy performance for the fabric, services and lighting specification. It also introduces a mandatory requirement for renewable sources. The renewable sources must in general provide 20% of the primary energy use, however there is flexibility where the building is more energy efficient than the regulations. This typically corresponds to an A3 Building Energy Rating.The NEAP Software for Non Residential Buildings has been updated to demonstrate compliance with NZEB and Part L of the Building Regulations. The SBEMie software version 5.5h is now available to the market for demonstrating compliance with NZEB requirements.


For major renovation

For existing buildings under EPBD, major renovation is where “more than 25% of the surface area of the building envelope undergoes renovation”. This will require that the building is brought up to cost optimal level, which is defined in the building regulations as:Upgrade Heating System more than 15 years’ oldUpgrade Cooling and Ventilation Systems more than 15 years’ oldUpgrade Lighting more than 15 years old.Further details can be found on the Department of Housing, Planning and Local Government website.



Requirements for Domestic Buildings

For new buildings

For all new builds, NZEB is equivalent to a 25% improvement in energy performance on the 2011 Building Regulations. A range of examples are shown in excel versions of the DEAP software available in the Domestic BER Resource page.


Key changes to Part L for NZEB compliance include a Maximum Energy Performance Coefficient of 0.3, a Maximum Carbon Performance of 0.35 and a renewable Energy Ratio of 20%.


For major renovation

For existing buildings, major renovation is typically activated under the following circumstances, where the work affects greater than 25% surface area of the existing dwelling:

External Wall Renovation, external or internal insulation

External Wall & Window Renovation

External Wall & Roof Renovation

External Wall & Floor Renovation


New Extension

The cost-optimal level is a primary energy performance of less than 125 kWh/m2/yr (B2 BER) when calculated using DEAP or upgrade of ceiling insulation and heating system.


Further details can be found on the Department of Housing, Planning and Local Government website.

Overheating risk in Dwellings

SEAI commissioned a study to assess the overheating risk in dwellings using CIBSE TM59 methodology and review the available risk assessment tools to avoid/minimise cooling being retrofitted in homes.To understand the risk of overheating and to inform the review of available tools, a range of typical dwellings with different fabric specifications and mitigation measures are modelled.


Cost Optimal Study

The Cost Optimal Study is required under the Energy Performance of Buildings Directive to define the energy performance required for New Buildings and Major Renovation. The study accounts for the capital, operational, maintenance and carbon costs of various energy efficient solutions and renewable technologies.


Domestic Cost Optimal Study The Domestic Cost Optimal was last updated in 2018.


Further details can be found on the Department of Housing, Planning and Local Government website.





Non Domestic Cost Optimal Study

The Non Domestic Cost Optimal was last updated in 2019.


Further details can be found on the Department of Housing, Planning and Local Government website.


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