What’s new with the updated Part L of the Building Regulations?

What’s new with the updated Part L of the Building Regulations?

With the release of the new Part L of the Building Regulations, it is now the perfect time to take a look at the new regulations and understand not only the changes that have been implemented, but also to look at the wider picture and understand why these changes to the regulations have been made. Here we will focus on the changes to the new-build homes, where the changes will be felt most.

So what are the changes?

The overarching theme of the update to the regulations is that it will be harder to achieve compliance, particularly due to the stricter fabric backstop values and air permeability results that have been proposed, as shown in Table 1.

Element type

Current regulations maximum U-value (W/m2K)

Proposed regulations maximum U-value (W/m2K)

Floor

0.25

0.18

External walls

0.30

0.26

All roof types

0.20

0.16

Party walls

0.20

0.20

Swimming pool basin

0.25

0.25

Windows (including roof windows)

2.0

1.6

Rooflights

2.0

2.2

Doors (including glazed doors)

2.0

1.6

Air permeability

10.0 m3/(h.m2) at 50 Pa

8.0 m3/(h.m2) at 50 Pa

Table 1- Current vs proposed backstop values

As can clearly be seen in Table 1, the 2021 Part L regulations will require elements to be built to a better thermal standard than before in order to meet these backstop values. In addition to the stricter U-value backstops for building elements, the air permeability has also been brought down from 10.0 m3/(h.m2) at 50 Pa to 8.0 m3/(h.m2) at 50 Pa. This requirement is also established as 1.57m3/(h/m2) @ 4Pa, which means that the alternative Pulse method of air testing can now be used for Building Regulations purposes. There is also an additional requirement that air pressure testing must be done on all properties, which was not previously the case.

The stricter changes do not stop there however, as the notional building has also been altered with stricter values that will make the Target Emission Rating (TER) more difficult to achieve as well. The changes to the notional building can be seen in Table 2.

Building envelope

Current regulations notional building U-value (W/m2K)

Proposed regulations notional building U-value (W/m2K)

Ground floor

0.13

0.13

External walls

0.18

0.18

Roofs

0.13

0.11

Party walls

0.0

0.0

Windows

1.4

1.2

Roof windows

1.4

1.2

Rooflights

N/A

1.7

Air permeability

5.0 m3/(h.m2) at 50 Pa

5.0 m3/(h.m2) at 50 Pa

Table 2- Current notional building parameters vs future notional building parameters

These values are just as important as the actual U-value backstop values, as it is these values that are used to build up the ‘Notional Building’ against which the actual building is compared. Thus, it is clearly evident that anyone building to the maximum allowable U-values and air permeability results will not achieve compliance with Part L1 without serious offsetting of emissions through renewable technologies. This is intended to drive housebuilders towards a ‘fabric first approach’, preventing poorly insulated homes from achieving compliance through excessive use of renewable technologies, particularly PV systems.

The new compliance metric- Target Primary Energy Rate

The updated Part L also introduces a third compliance metric to go alongside the existing Target Emission Rate (TER) and Target Fabric Energy Efficiency (TFEE), which will be known as the Target Primary Energy Rate (TPER).

The Target Primary Energy Rate (TPER) is defined in kWhPE/m2/year, and is the maximum allowable primary energy usage by the dwelling. Primary energy is defined by the BRE as “energy from renewable and non-renewable sources which has not undergone any conversion of transformation process”. To illustrate what this means, the energy contained in fossil fuels is a source of primary energy, however, a unit of electricity produced by burning that fossil fuel would not be considered primary energy, as it had to go through a conversion process. The calculation accounts for factors such as:

  • The efficiency of the property’s heating system;
  • Power station efficiency for electricity; and
  • The energy used to produce the fuel and deliver it to the property.

The Primary Energy metric therefore takes into account upstream energy uses, i.e. the energy used to produce the fuel before it is used in the dwelling. These are accounted for when producing the Primary Energy Rate by converting the energy consumption using a Primary Energy Factor. The Primary Energy Factor differs depending on the fuel type and indicates how many kWh of energy were used to produce 1 kWh of energy used in the dwelling. For example, the Primary Energy Factor for natural gas is 1.130 kWh/kWh, meaning 1.13 kWh of energy is used in the extraction and transportation of the natural gas for each 1 kWh supplied to the dwelling.

As with the other two existing compliance metrics, the target value will be set according to the notional building specification.

What does this mean for product manufacturers?

Product manufacturers will need to look at how these new regulations will affect their products. Putting in both existing and future products into a range of different archetypes of buildings is something that will give product manufacturers a good idea of how their product performs under these new regulations. Determining this performance against these new standards is crucial in order to keep pace with competitors and ensure the viability of their product.

Conclusion

The new regulations are a welcome change from the long outdated 2013 regulations. Improving the energy efficiency of new homes through these changes will ideally result in lower running costs for occupants and lower carbon emissions than under the previous regulations. However, how the impact these changes have on the cost of construction, as well as other aspects of building comfort (such as ventilation) remains to be seen in the real world.


Interested in modelling your products against the new Part L?

We can model your products in different building archetypes to see how they effect the energy ratings. This is an invaluable tool to demonstrate the energy performance of your products in homes built to future Building Regulations, which you can include in your company's marketing and PR activities to help win more business. Find out more about Product Modelling


Article published 21/12/21

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