Three acronyms decide how your house is built and how it is graded at the end. They are related but not the same thing, and mixing them up is how people end up designing to the wrong target.
Part L is the rule
Part L of the Building Regulations sets the conservation of fuel and energy requirements for a new dwelling. Compliance is demonstrated through DEAP, the calculation methodology, and it constrains fabric performance, airtightness, ventilation, the heating system and the renewable energy contribution together — not one at a time.
NZEB is the level
Nearly Zero Energy Building is the performance level new dwellings have to reach. In practice it means a very good fabric, a heat pump rather than a fossil fuel boiler in most designs, controlled ventilation, and an airtightness result that has to be tested, not assumed.
BER is the label — and it changed in 2026
On 24 May 2026 the Building Energy Rating scale was simplified. The fifteen old levels became eight bands: A0, A, B, C, D, E, F and G. The sub-categories such as A1, A2, A3, B1, B2 and B3 were removed. A0 is a new top band for buildings that are highly energy-efficient and use no fossil fuels. Certificates issued before the change stay valid for their ten years.
What the fabric has to do
| Element | What matters | Frest Als build-up |
|---|---|---|
| Walls | U-value and no repeating cold bridge | 290–300 mm insulation in a 371 mm wall |
| Roof | Depth of insulation, continuity at eaves | 250–300 mm |
| Floor | Perimeter cold bridge is the weak point | 250 mm under the slab |
| Windows | Whole-window U-value, not glass only | Triple glazed |
| Airtightness | A continuous, drawn, buildable line | Vapour control layer detailed in the factory |
| Ventilation | Heat recovery, commissioned and balanced | MVHR-ready, installed locally |
Where factory manufacture helps and where it does not
It helps with the fabric: panels are built indoors to a jig, the insulation never gets wet, and the airtightness layer is installed in controlled conditions rather than in February rain. It does nothing for your heat pump sizing, your ventilation commissioning or your DEAP assessment, all of which are done in Ireland by Irish professionals. A superb frame with an uncommissioned ventilation system is a bad house.
Frequently asked questions
What BER will a new house get in 2026?
A new dwelling built to Part L and NZEB will normally land at A, and can reach A0 where the design uses no fossil fuel and the fabric and systems are strong. The actual result comes from the DEAP assessment of your specific house.
Do the old A1, A2 and A3 ratings still exist?
Not on new certificates. Since 24 May 2026 the scale is A0, A, B, C, D, E, F, G. Existing certificates remain valid for ten years from issue.
Is an airtightness test mandatory?
Yes, a test result is required for the DEAP calculation on a new dwelling. Design for it from the first drawing; it is very hard to fix afterwards.
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