Technical Booklet F – Northern Ireland
On 30th June 2022, a revised version of Part F to the Building Regulations came into force in Northern Ireland. This is supported by new TBF (TBF 2022).
In 2023, the Department of Finance ran a consultation to look at further updates to Part F expected to come into force in 2024 and 2026/7 respectively. The outcomes from this consultation are yet to be published.
TBF 2022 – came into force 30th June 2022
There are two Technical Booklets F:
Technical Booklet F1, Conservation of fuel and power in dwellings (TBF1)
Technical Booklet F2, Conservation of fuel and power in buildings other than dwellings (TBF2)
Each booklet sets out what, in ordinary circumstances, may be accepted as reasonable provision for compliance with the energy efficiency requirements of the Building Regulations for the type of building work in question.
New buildings
The Technical Booklets include key metrics which all new build dwellings and non-domestic buildings must meet. These are:
- Carbon emissions – which sets the maximum expected operational carbon emissions from a building.
- Minimum acceptable standards – which set the worst acceptable standards for air permeability, building services and for the area-weighted U-values that walls, floors and roofs must achieve across their total area.
Carbon emissions are set via modelling software (e.g. SAP for domestic, SBEM for non-domestic). An energy assessor inputs the building dimensions into the software. The software will then apply a set Notional Dwelling / Building specification to a theoretical building of the same dimensions. From this, it generates the Target Emission Rate (TER). This is compared against a Dwelling Emission Rate (DER) or Building Emission Rate (BER) which is generated based on the actual building specification.
Following the update to TBF 2022, the DER/BER for new build projects must now achieve minimum percentage improvement on the TER. These are:
- Dwelling houses – 40% improvement on the TER
- Flats – 25% improvement on the TER
- New builds other than dwellings – 15% improvement on the TER.
The Minimum Acceptable U-values for the building fabric are shown in the tables below. It is important to note that these are the worst acceptable area-weighted values, in order to reach a compliant DER/BER it may be necessary to achieve lower U-values in some or all elements.
As the Minimum Acceptable U-values are area-weighted, certain areas of the construction can be insulated to a worse level providing this is compensated elsewhere in the construction. In all cases, however, no single point should be insulated to a worse level than the Worst Case Point U-values shown in the tables.
Domestic
Element type | Minimum Acceptable U-values - area-weighted (W/m2K) | Worst Case Point U-values (W/m2K) |
Wall | 0.18 | 0.60 |
Floor | 0.18 (0.15 if underfloor heating is used) | 0.60 |
Roof | 0.16 | 0.30 |
Non-domestic
Element type | Minimum Acceptable U-values - area-weighted (W/m2K) | Worst Case Point U-values (W/m2K) |
Wall | 0.21 | 0.60 |
Floor | 0.21 | 0.60 |
Roof | 0.16 (pitched), 0.20 (flat) | 0.30 |
Existing buildings
Certain works on existing buildings may also be covered by the requirements of TBF 2022. The requirements vary depending on whether it is a new / replacement thermal element, a renovated element, an extension or a change of use / energy status.
Adding or replacing thermal elements
These apply where:
- a new thermal element is added (such as a dormer window); or
- a thermal element is replaced (such as a reroofing).
On these projects, thermal elements will typically be expected to meet, or improve on, the area-weighted average maximum U-values shown in the table below.
Element type | Maximum U-value for new elements - area-weighted (W/m2K) |
Wall | 0.28 |
Floor | 0.22 |
Pitched roof - insulation at ceiling level | 0.16 |
Pitched roof - insulation at rafter level | 0.18 |
Flat roof or roof with integral insulation | 0.18 |
As these are area-weighted average U-values, it is possible to insulate certain areas of an element to worse U-values, provided this is compensated for elsewhere in the construction. In all cases, the U-values should be no worse than the limiting U-values (0.60 W/m2K - walls and floors, 0.30 W/m2K – roofs).
Consequential improvements may also apply to the existing buildings with a useable floor area over 1000 m2 depending on the type of work being carried out (typically for extensions).
See the relevant Technical Booklet for further details on consequential improvements and design flexibility options.
Renovated elements
Separate improved U-values are applied when undertaking certain renovation works on an existing thermal element. These renovation works include:
- fitting a new layer of cladding or render on the outside of a thermal element
- drylining the internal surface of a thermal element
- stripping down a thermal element to the basic structural components then rebuilding
- replacing the waterproof membrane on a flat roof
- adding cavity wall insulation
- where more than 50% of the surface of an individual element is renovated (for example, by applying cladding, render or a waterproof membrane), or more than 25% of the surface area of the external envelope is renovated (for example, by fitting drylining).
Ideally, this work should look to achieve the Upgraded U-values shown in the table below as a minimum. Where this isn’t technically feasible, or will not provide payback within 15 years, you should look to achieve the best possible U-values which are achievable. In all cases, you should reach, or improve upon, the 'Threshold U-values' shown below.
Element type | Upgraded U-values - area-weighted average (W/m2K) | Threshold U-values for retained fabric (W/m2K) |
Pitched roof - insulated at ceiling level | 0.16 | 0.35 |
Pitched roof - insulated at / between rafters | 0.18 | 0.35 |
Flat roof or roof with integral insulation | 0.18 | 0.35 |
Wall - cavity insulation | 0.30 | 0.70 |
Wall - internal or external insulation | 0.30 | 0.70 |
Floor | 0.25 | 0.70 |
Building an extension
When constructing an extension using Standards Based Approach, all new elements will need to meet the requirements for adding and replacing thermal elements whilst any refurbished thermal elements will need to meet those for renovated thermal elements.
For non-domestic buildings where the proposed extension has a useful floor area that is both:
- greater than 100 m2 and
- greater than 25% of the existing useful floor area.
The extension must meet the TER for new buildings without any percentage uplift.
If greater flexibility is needed, project teams can also choose to take a Calculated Trade-off Approach or Equivalent Carbon Target Approach.
In a Calculated Trade-off Approach, the U-values of the elements in the construction can be varied from the Standards Based Approach providing the area-weighted U-value of all the elements combined is no greater than that of an extension of the same size and shape that uses the Standard Based Approach U-values.
In the Equivalent Carbon Target Approach, SAP or SBEM can be used to prove the that the predicted carbon emissions rate from the dwelling or building and the extension is no higher than for the notional version. If, as part of achieving this, upgrades are proposed to the existing dwelling or building, these should be no worse than the Upgraded U-values for renovated elements.
If the floor area of the building is over 1000 m2, then any extension will also trigger consequential improvements to raise the energy efficiency for the whole building. See the relevant Approved Document for further details.
Change of use or energy status
When a building or a section of a building is subject to a change of use (e.g. from office to apartments) or to a change in energy status (e.g. where a loft or garage is converted to become part of the heated building) then the elements within this space must meet the requirements for adding or replacing thermal elements or renovating thermal elements as is appropriate for the work.
Where design flexibility is required, an Equivalent Carbon Target Approach can be used. This requires use of SAP or SBEM to demonstrate that the calculated carbon dioxide emission rate from the building is no greater than that of a notional building of the same size complying with the Standards Based Approach.
Page updated 16/07/2025
U-value calculator
Try our free online U-value calculator to calculate the thickness of material needed to meet the new levels of thermal performance. With a number of roof, wall and floor constructions, the calculator is quick and easy to use.
