What changes are expected in Part L 2020?

28 September 2020 Kingspan Insulation UK
Building Regulations

Before the end of the year, England and Wales are expected to publish their revised versions of Part L to the Building Regulations for new homes. These documents set limits on the energy demand of properties and the upcoming updates are designed to provide a stepping-stone to even more stringent requirements coming in 2025. As such, rather than simply looking to comply, the construction industry should look to the changes as an opportunity to upskill, gaining the training and experience needed to be fully ready for the developments ahead. In this blog, we take a look at the expected changes.

What is the difference between Part L and Approved Document L?
The terms ‘Part L’ and ‘Approved Document L (ADL)’ come up frequently when the Building Regulations are discussed. It is important to understand that these are not the same document. 

Part L is a section of the Building Regulations document and it is compulsory for all buildings to meet its requirements. ADL is a guidance document designed to support project teams in achieving compliance with Part L requirements. It is separated into four parts:
•    ADL1A – New domestic
•    ADL1B – Existing domestic
•    ADL2A – New non-domestic
•    ADL2B – Existing non-domestic

If a building is completed in accordance with the guidance within ADL it should be compliant with Part L.

What are the new carbon reduction targets?
The consultations provided two options for reducing carbon emission targets. In the English consultation, these were for a 20% or 31% (preferred) reduction over the existing requirements whilst in Wales more ambitious targets of 37% (preferred) or 56% were set.

What is Primary Energy?
Primary Energy has been introduced as the new principal metric within the revised regulations, with carbon emissions now relegated to a secondary metric. Primary is designed to consider both the energy needed to prepare a fuel for use, and the final energy demand of the property.

The move away from using carbon emissions to set performance levels reflects the expectation that grid energy will be increasingly decarbonised over coming years (as discussed in the first blog in this series).   As this process continues, carbon emissions will therefore become a less useful measure of how responsibly a building uses energy.

How is Primary Energy calculated?
Primary Energy Factors (PEFs) have been pre-calculated (within SAP) for each common fuel type based on upstream production activities needed to get them to market. These include planting and cultivation of biofuels, extraction and transportation.

A property’s energy demand for each use (space heating, lighting etc.) is calculated and these are multiplied by the PEF of the fuel type used for each. By adding these together, we get a total Primary Energy demand for the property.

For example, Primary Energy demand for heating is calculated through the following equation:

(property energy demand/ efficiency of heating technology) x PEF 

Let’s assume the property is heated with 100% efficient electric panel heaters with an overall heating demand of 10,000 kWh. The fuel factor for electricity is 1.501 so Primary Energy demand is calculated as follows:

(10,000 kWh / 1) x 1.501 = 15,010 kWh

Importantly, the Primary Energy calculation allows any energy generated by onsite renewable technologies, such as photovoltaic (PV) panels, to be subtracted from the overall energy demand. For example, if we added a PV array generating 1,500 kWh specifically for use within the property described above, then the calculation would be changed as follows:

([10,000 kWh – 1,500 kWh]/1) x 1.501 = 12,759 kWh

What are the limitations of the new Part L requirements outlined within the consultations?
A key area of concern raised by several respondents to the English consultation was the suggestion that the Fabric Energy Efficiency Standards (FEES) should be removed. The FEES are used in the current version of ADL1A in England to set a clear minimum energy performance target, however, the consultation argued it should be removed to avoid confusion with the Primary Energy metric.  

Without the FEES, the only control on building fabric performance would be the worst-case backstop U-values. This is the approach which is already used in Wales (which never adopted the FEES), however, the backstop values proposed in the English consultation are weaker than even the current ones in Wales (shown in table 1).
Heat Loss Elements Current England ADL1A Current Welsh ADL1A England 2020 Proposed Wales 2020 Proposed
Floors 0.25 W/m²K 0.18 W/m²K 0.18 W/m²K 0.15 W/m²K
External Walls 0.30 W/m²K 0.21 W/m²K 0.26 W/m²K 0.18 (Flats 0.21) W/m²K
Flat and Pitched Roofs 0.20 W/m²K 0.15 W/m²K 0.16 W/m²K 0.13 W/m²K
Table 1 - Area weighted worst-case backstop U-values for new domestic buildings.

With the Primary Energy calculation allowing onsite renewable generation to be subtracted from overall demand, this could open the door for homes to be built to lower standards of fabric performance than the current standards (with FEES) will allow, providing it is masked with generation from onsite renewables.

In essence, this could create homes which waste considerable amounts of energy. In fact the Committee on Climate Change estimated that it could lead to household bills which are 50% higher than at present – potentially pushing owners towards fuel poverty. Furthermore, during the winter months when demand is high, technologies such as heat pumps and photovoltaic (PV) panels are less effective. This could place additional pressure on the grid and actually mean carbon intensities during this period creep up.

For these reasons, Kingspan believes it makes much more sense to adopt a whole building approach which focuses on limiting demand through measures including improved fabric performance and careful detailing before considering renewable options.

What U-values will new homes be expected to achieve under Part L 2020?
The suggested fabric parameters provided within the notional dwelling for Option 1 of the English consultation and Option 1 and 2 of the Welsh consultation provide a reasonable starting point. Whilst not compulsory, these values are expected to become the limiting back-stop U-values within the region’s 2025 standards so it makes sense for firms to begin familiarising themselves with the approaches needed to achieve these values routinely in the future.

  2020 English Proposal Option 1 2020 Welsh Proposal Option 1 & 2
Floors 0.11 W/m²K 0.11 W/m²K
External Walls 0.15 W/m²K 0.13 W/m²K
Flat and Pitched Roofs 0.11 W/m²K 0.11 W/m²K
Table 2 - Proposed U-values for notional dwelling within English and Welsh ADL1A 2020

Why are Approved Construction Details being removed?
The Approved Construction Details (ACDs) were first developed as a standardised solution to help project teams to address common thermal bridges. In practice, however, contractors regularly come across non-standard junctions and if the solution isn’t adapted appropriately this can lead to thermal bridging and underperformance. 

To address this, the consultations have recommended that the ACDs are removed and that project teams work to model/calculate their own thermal bridging values. To encourage this, the global backstop values for thermal bridging (used where no appropriate detail is provided) will be worsened in SAP. This ultimately means that paying attention to details will be crucial to achieving compliance.

Preparing for the future
As we discussed in the previous blog in this series , the pace of change in industry requirements is expected to be rapid over the coming years. As such, it is essential that practitioners really get to grips with the new Part L, and the overall direction of travel, to ensure they are properly prepared for the challenges ahead.

Other blogs in this series

Kingspan Insulation Ltd

For queries relating to insulation boards, cavity closers or membranes.





General enquiries: 01544 388 601

Architect Technical Helpline:
01544 387 382