Technical Guidance Document L – Republic of Ireland
On 25th October 2022, a revised version of Part L to the Building Regulations came into force in Republic of Ireland. This is supported by new TGDL (TGDL 2022).
TGDL 2022 – came into force 25th October 2022
There are two Technical Guidance Documents L:
Technical Guidance Document L 2022, Conservation of Fuel and Energy – Dwellings
Technical Guidance Document L 2022, Conservation of Fuel and Energy – Buildings other than Dwellings
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 Guidance Documents include key metrics which all new build dwellings and non-domestic buildings must meet. These are:
- Primary Energy - which considers both the energy used within the building, and the energy used in upstream activities to prepare the fuel and losses from transmission/distribution.
- Carbon Emissions – which sets the maximum expected operational carbon emissions from a building.
- Minimum renewable provision – which sets a minimum percentage of Primary Energy which must be met via renewable energy technologies.
- Minimum acceptable fabric 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. DEAP for domestic, NEAP for non-domestic). An energy assessor inputs the actual building dimensions into the software. The software then calculates two outputs:
- Proposed Building - the calculated primary energy consumption and CO2 emissions for the dwelling based on the proposed specification.
- Reference Building - the calculated primary energy consumption and CO2 emissions for a Reference Building of the same dimensions as the Proposed Building based on a standard Reference Specification.
The Primary Energy consumption and CO2 emissions from the Proposed Building are then divided by those for the Reference Building to produce the Energy Performance Coefficient (EPC) and Carbon Performance Coefficient (CPC). These must match, or improve on, Maximum Permitted Energy Performance Coefficient (MPEPC) and Maximum Permitted Carbon Performance Coefficient (MPCPC) for the building to be deemed compliant.
A Renewable Energy Ratio (RER) is also set to ensure a minimum level of renewable energy provision. This is based on the ratio of primary energy from renewable sources to the total primary energy demand of the Proposed Building as calculated in DEAP or NEAP.
The MPEPC, MPCPC and RER for different building types are shown in the table below.
| Domestic | Non-domestic |
Maximum Permitted Energy Performance Coefficient (MPEPC) | 0.3 | 1.0 |
Maximum Permitted Carbon Performance Coefficient (MPCPC) | 0.35 | 1.15 |
Renewable Energy Ratio (RER) | 0.20 | 0.20 (0.10 if EPC is 0.9 and CPC is 1.04) |
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 and, 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 |
Pitched roof | 0.16 | 0.30 |
Flat roof | 0.20 | 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 |
Pitched roof | 0.16 | 0.30 |
Flat roof | 0.20 | 0.30 |
Existing buildings
Certain works on existing buildings may also be covered by the requirements of TGDL 2022.
Material alterations and material change of use
Where a building or space is subject to material alterations or change of use, project teams should look to achieve the area-weighted average U-values shown in column 2 below. For non-domestic projects, this applies to retained thermal elements which exceed the threshold U-values in column 3.
These can be relaxed for individual constructions or areas of constructions if required for design or construction reasons, providing these areas at least meet the elemental U-value shown below. Where values are relaxed, these should be compensated for with improved U-values in other areas.
Element type | Area-weighted average (W/m2K) | Area-weighted threshold (W/m2K) | Elemental U-value (W/m2K) |
Pitched roof -insulated at ceiling level | 0.16 | 0.16 | 0.35 |
Pitched roof - insulated at/between rafters | 0.25 | 0.35 | 0.35 |
Flat roof or roof with integral insulation | 0.25 | 0.35 | 0.35 |
Wall - cavity insulation | 0.55 | 0.55 | 0.60 |
Wall - internal or external insulation | 0.35 | 0.55 | 0.60 |
Ground floors | 0.45 | 0.45 | 0.60 |
Major renovations
Where more than 25% of the surface area of the building envelope undergoes renovation, the whole building must be improved to “Cost Optimal” level where this is technically, functionally and economically feasible. Work to the surface area can include:
- recladding walls
- replacing windows
- drylining internally.
The ”Cost Optimal” performance level requires the building to achieve a set energy performance level calculated in DEAP or NEAP (see relevant technical guidance document for details). On domestic projects, this may include upgrading roofs insulated at ceiling level to the area-weighted average U-value shown in column 2 above (see relevant technical guidance document for details).
Building an extension
For extensions, project teams should look to achieve the Minimum Acceptable U-values for new build projects (shown in the tables above). To provide more flexibility, project teams can choose to vary the U-value of individual elements providing all areas at least achieve the Worst Case Point U-values and that this is compensated by upgrading other elements so that the overall heat loss through the walls, roof and floor combined is no higher than if the area-weighted values were used.
Page reviewed 07/07/2025
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.
