What is NZEB (nearly zero energy building)?

How it works in Ireland

The law requires a very high fabric standard, efficient heating with controls, and a significant share of energy from renewables. In practice that means a well-insulated, airtight house and a low-temperature heating system. Your designer proves it with a calculation in the Dwelling Energy Assessment Procedure (DEAP), the same software behind the BER.

The guidance expresses NZEB as three whole-house targets: an Energy Performance Coefficient (EPC), a ratio of the house’s calculated primary energy to a reference dwelling, of no more than 0.30; a Carbon Performance Coefficient (CPC); and a renewable energy ratio of at least 20%. Meeting a single target is not enough. All three, plus the other Part L provisions such as limiting thermal bridging and testing airtightness, must pass.

NZEB is the legal minimum. It is not Passive House, which is a voluntary and stricter certification. The standard applies from your commencement date, so if work starts a year late, check which version of the guidance applies.

A major renovation of more than 25% of the building envelope must be upgraded to cost-optimal level where feasible, which matters if you are rebuilding an existing house.

Two practical checks help. First, ask for the airtightness test target at design stage, because the test is done near the end and a failed result is expensive to fix once the plaster is on. Second, ask your designer how the result changes if you swap the heating system or remove a window, so you know which choices are safe to change later and which are not. Keep the DEAP report with your completion papers, since your assessor, lender and a future buyer may all ask for it.

A common mistake

Treating the standard as the builder’s problem at the end. The calculation drives choices made at design stage: wall build-up, windows, the heating system and any panels. Ask your designer for the DEAP result before the drawings are finished, and again as built, so the BER at completion matches what you were told.