Completely free — choose N. Ireland under the verdict and the tables switch.
Opens on a wall with the Northern Ireland dwelling tables selected. Change the nation or building type at any time.
Dwellings — Technical Booklet F1: 2022
| Element | Table 2.2 — new dwelling, area-weighted average | Table 2.2 — worst at any point | Table 3.2 — new element in an existing dwelling | Table 3.3 — retained: threshold → upgraded |
|---|---|---|---|---|
| Wall | 0.18 | 0.60 | 0.28 | 0.70 → 0.55 cavity / 0.30 internal or external insulation |
| Floor | 0.18 (0.15 with underfloor heating) | 0.60 | 0.22 | 0.70 → 0.25 |
| Pitched roof, insulation at ceiling | 0.16 | 0.30 | 0.16 | 0.35 → 0.16 |
| Pitched roof, insulation at or between rafters | 0.16 | 0.30 | 0.18 | 0.35 → 0.18 |
| Flat roof | 0.16 | 0.30 | 0.18 | 0.35 → 0.18 |
| Party wall | 0.00 | 0.60 | — | — |
| Windows and doors | 1.40 | 3.00 | — | — |
All values W/m²K. Source: Technical Booklet F1: 2022, Conservation of fuel and power in dwellings (Northern Ireland) — Table 2.2 p.30, Table 2.3 p.33, Table 3.2 p.48 (paras 3.10(c) and 3.52), Table 3.3 p.50. Read 10 October 2026.
Party walls — F1 Table 2.3
| Construction | U-value to use |
|---|---|
| Solid | 0.00 |
| Unfilled cavity with effective edge sealing | 0.20 |
| Fully filled cavity with effective edge sealing | 0.00 |
Buildings other than dwellings — Technical Booklet F2: 2022
| Element | Table 2.3 — new building, area-weighted average | Table 3.3 — new element in an existing building | Table 3.4 — retained: threshold → upgraded |
|---|---|---|---|
| Wall | 0.21 | 0.28 | 0.70 → 0.55 cavity / 0.30 internal or external insulation |
| Floor | 0.21 | 0.22 | 0.70 → 0.25 |
| Pitched roof | 0.16 | 0.16 at ceiling / 0.18 at rafter | 0.35 → 0.16 at ceiling / 0.18 at or between rafters |
| Flat roof | 0.20 | 0.18 | 0.35 → 0.18 |
| Party wall | 0.20 | — | — |
| Windows, pedestrian doors | 1.60 | — | — |
Source: Technical Booklet F2: 2022, Conservation of fuel and power in buildings other than dwellings (Northern Ireland) — Table 2.3 p.34 (worst at any point: walls and floors 0.60, roofs 0.30), Table 3.3 p.59, Table 3.4 p.62. Read 10 October 2026.
How U-Monkey applies it
New build is judged against the Table 2.2 (F1) or Table 2.3 (F2) average; a new element in an extension or conversion against Table 3.2 (F1) or 3.3 (F2); an existing element as built against the Table 3.3 / 3.4 threshold; and a retained element being renovated against the upgraded value — cavity or solid wall, floor or roof. Windows and doors entered as specified elements use the same booklets. Type a BT postcode in “Judged as” and Northern Ireland is selected for you, along with the nearest climate station (Belfast Aldergrove) for the condensation check.
Frequently asked questions
What U-values does a new house need in Northern Ireland?
Technical Booklet F1: 2022, Table 2.2, sets area-weighted average limits: walls 0.18, floors 0.18 (0.15 with underfloor heating), roofs 0.16, party walls 0.00, and windows and doors 1.40 W/m²K. It also sets a worst value at any single point: walls and floors 0.60, roofs 0.30, party walls 0.60, windows 3.00. The dwelling must also meet its overall emission and energy targets.
And for an extension in Northern Ireland?
A new thermal element in an existing dwelling — an extension, or a new or replacement element — is judged by F1 Table 3.2: walls 0.28, pitched roofs insulated at ceiling 0.16, at rafter 0.18, flat roofs 0.18, floors 0.22. Those are looser than England’s Table 4.2 (walls and floors 0.18, roofs 0.15), so the nation really does change the answer.
When does an existing wall, roof or floor have to be upgraded?
F1 Table 3.3: a cavity wall worse than 0.70 is upgraded to 0.55, a wall insulated internally or externally to 0.30, a pitched roof insulated at ceiling worse than 0.35 to 0.16, at or between the rafters to 0.18, a flat roof to 0.18 and a floor worse than 0.70 to 0.25.
What about party walls?
F1 Table 2.3 assigns them: a solid party wall 0.00, an unfilled cavity with effective edge sealing 0.20, a fully filled cavity with effective edge sealing 0.00. The Table 2.2 limit is 0.00, so in practice a new party wall is solid or fully filled and sealed.
Does U-Monkey use the Northern Ireland booklets?
Yes. Choose N. Ireland under the verdict (or type a BT postcode) and the pass/fail, the hints and the PDF switch to Technical Booklet F1 or F2 and name the table. The U-value calculation itself (BS EN ISO 6946, BR 443) is the same across the UK.
Elsewhere: England · Wales · Scotland (Section 6) · Republic of Ireland · non-domestic buildings. Full tutorial: how to use U-Monkey.