Meet the nZEB and Part L energy rules for your house

Ask your designer to check your insulation, heating, ventilation and renewables together before you seek quotes. New houses must meet the nearly zero energy building (nZEB) standard, so each choice affects the whole-house energy calculation and your budget.

Use the Part L regulations, the applicable Technical Guidance Document (TGD) and the Sustainable Energy Authority of Ireland (SEAI) assessment method together. Ask your designer to record the editions, transitional provisions and targets that apply to your house.

If you are considering a higher voluntary standard, compare Passive House certification with nZEB. For booking the final assessment and collecting the certificate, use the new-home BER guide.

Which energy rules cover your build?

Part L of the Building Regulations deals with conserving fuel and energy. For new dwellings, the European Union (Energy Performance of Buildings) Regulations 2019 (S.I. 183/2019) set nearly zero energy requirements from 1 November 2019, subject to transitional arrangements. They also cover major renovations. Their exemptions include protected and proposed protected structures and specified national monuments; do not treat that as a blanket exemption from every building requirement.

What Regulation 8 requires of a new dwelling

Regulation 8 sets six requirements, listed below. Ask your designer to show how the design meets each. The house must limit energy use and carbon emissions, use renewables, retain heat and have efficient systems you can operate:

Check	Design requirement
Energy and carbon	Limit calculated primary energy use and related carbon dioxide (CO₂) emissions to nZEB levels, insofar as reasonably practicable
Renewables	Cover the nearly zero or very low energy requirement to a very significant extent with renewables produced on site or nearby
Building fabric	Limit heat loss through insulation, windows, thermal bridging and airtightness; use heat gains where appropriate, including solar orientation
Heating	Provide and commission efficient space and water heating, with efficient heat sources and effective controls
Oil and gas boilers	Meet a minimum seasonal efficiency of 90%
Handover	Give you enough information about the building, fixed services, controls and maintenance to operate it without wasting energy

The energy and carbon limits are calculated using the Dwelling Energy Assessment Procedure (DEAP) published by SEAI. Regulation 8 refers to nZEB as defined in the European energy-performance Directive; the numerical targets come from the technical guidance. Meeting an individual product specification does not establish that the whole house passes.

Check the three whole-house targets

Regulation 9 allows the Minister to publish technical guidance. Following it is evidence of compliance; other suitable materials, methods or specifications can also comply. Your designer should identify and document the compliance route.

The Part L guidance for dwellings uses three measures from the DEAP calculation. Check your design against these nZEB thresholds for new dwellings:

• an Energy Performance Coefficient (EPC), a ratio of the dwelling’s calculated primary energy to a reference dwelling (maximum 0.30);
• a Carbon Performance Coefficient (CPC), the same idea for CO₂ emissions (maximum 0.35);
• a Renewable Energy Ratio (RER), the share of primary energy met by renewables (minimum 20%).

These are targets for the whole house, not for individual products, so your designer chooses a combination of fabric, heating and renewables that passes. That freedom is also why two nZEB houses can cost quite different amounts.

Which edition applies to you

Regulation 6 applies the 2019 regulations to works in connection with a new dwelling that commence on or after 1 November 2019, with a transitional exception. A dwelling stayed outside if both of these held:

1. an application for planning permission (or approval) was made on or before 31 October 2019, or a Part 8 notice (a council’s public notice of its own development) was published on or before that date; and
2. substantial work was completed by 31 October 2020. The regulation defines “substantial work” as the structure of the external walls having been erected.

That transitional window closed years ago, so for a house you start now the standard applies in full. The more relevant question is whether a later revision of the TGD has a transitional rule that affects a project with planning permission already granted. Ask your designer to check and record those dates before finalising the specification.

Renovations and extensions

The regulations apply to a major renovation: renovation of a building where more than 25% of the surface of the building envelope undergoes renovation. The “envelope” is every surface through which the building can lose heat to the outside or the ground: walls, windows, floors and roof. When a dwelling undergoes a major renovation, its minimum energy performance, or that of the renovated part, must be upgraded to the cost-optimal level, so far as technically, functionally and economically feasible.

Cost-optimal means the level that gives the lowest cost over the estimated economic lifecycle, counting investment, maintenance, operating and energy costs and, where relevant, disposal. In plain terms it is a cost-benefit test, not a fixed U-value. Smaller works may still have Part L obligations. An extension can also contribute to triggering the major-renovation threshold; have the designer check the affected envelope area. If your project includes an existing building, ask the designer to distinguish its renovation requirements from the new-dwelling specification before seeking quotes.

Include the energy requirements in your build budget

Agree these design and evidence tasks before placing orders:

• Airtightness and ventilation travel together. A very airtight house needs a planned ventilation strategy. That links Part L to Part F (ventilation). See building regulations for self-builds.
• Heating is a renewable decision, not just a boiler choice. Because the renewable contribution is a legal requirement, the heating system and any on-site generation are designed together early, not left until the final fitting-out stage.
• Keep compliance evidence. Agree the testing, installation records and commissioning documents with your designer. For the statutory certification route, these support the completion submission. Some single houses can skip the assigned-certifier system (see the certificate of compliance guide), but still have to comply with the Building Regulations. See certificate of compliance on completion.
• Check the Building Energy Rating (BER) during design. The same assessment software and method produce the rating you will need to sell or let. If the design result is weak, ask your designer to revise the specification before construction; do not rely on later site changes to improve it.
• Budget. Energy-driven items (insulation, windows, heat pump, ventilation, solar panels) are a significant line in the build budget. Ask your designer to price the compliant specification, not a baseline you will have to uprate.

Questions to ask your designer

1. Which edition of the Part L guidance applies to my commencement date, and what energy, carbon and renewable targets must the design meet?
2. What is the preliminary DEAP result for this design, and how much margin is there?
3. How will we meet the renewable requirement, and what does it cost to install and maintain?
4. What airtightness target is the design assuming, and who will test it, and when?
5. How is ventilation designed, and who commissions it?
6. What happens to the numbers if I swap a window, change the heating system or reduce the insulation to save money?

Agree inspection hold points with your designer and, where appointed, your assigned certifier. See assigned certifier explained.

To choose the heating and renewables that get you there, read the heat pump guide and the solar PV guide.