England Part L 2021 – Existing Homes

14 July 2021 Kingspan Insulation UK
Image of terraced houses

As part of its Future Buildings Standard consultation, the government earlier this year consulted on changes to the requirements within Part L of the Building Regulations  for existing homes and other dwellings in England. In this blog, we look at the key changes which have been proposed.

1. Tougher minimum standards for new and replacement thermal elements

Perhaps the most notable proposed change is the uplift in the minimum fabric standards for new and replacement thermal elements within existing homes. These apply when providing a new element (such as an extension) or when completely removing and replacing any thermal element (although exemptions exist for ground floor porches or conservatories with floor areas of less than 30 m2).

The new U-values for the different elements are shown in the table below. These have been developed based on a full lifecycle cost analysis to provide a good balance of fabric performance and cost effectiveness. They represent a substantive step-up from the existing requirements, particularly for external walls. The requirements for roofs have also been streamlined with a single U-value provided for all constructions.
Element type Current new element limiting U-values (L1A 2013) Proposed 2021 new element area weighted limiting U-values
All roof types N/A 0.15
-Pitched roof 0.18
-Ceiling level 0.16
-Flat roof 0.18
Walls 0.28 0.18
Floors 0.22 0.18
Swimming pool basin 0.25 0.25
Windows 2.00 1.40 or WER B
Rooflights 2.00 2.20
Doors with glazing 2.00 1.40 or DER C
Other doors 2.00 1.40 or DER B

2.    Primary Energy & FEES introduced for ‘greater design flexibility’ SAP method

As with the existing Part L, it is recognised that it may not always be possible or cost effective to meet the minimum requirements for all elements due to design constraints within the building. 

In the current version of Part L, two alternative methods are offered to demonstrate compliance.

1.    Project teams can choose to upgrade the U-value in some fabric elements to compensate for underperformance in another. For example, targeting lower U-values for external walls so that a slimmer thickness of insulation can be used on the floor. When adopting this approach, they need to demonstrate that the area weighted U-value of all the elements in the extension is no greater than that of an extension of the same dimensions which complies with the minimum U-value standards.

2.    Using SAP to demonstrate that CO2 emissions from the building and proposed extension are no greater than that for the building plus a notional extension of the same dimensions built to the minimum standards.

The consultation notes that as the second route focuses solely on CO2 emissions, it could allow extensions to be constructed to much worse fabric standards if a low carbon heating appliance, such as a heat pump, is installed. This could create spaces with high levels of heat loss which are expensive to heat. 

To avoid this, the consultation proposes that Primary Energy and Fabric Energy Efficiency metrics are introduced alongside the existing Dwelling Emission Rate to the SAP method of compliance. This is a sensible step which should ensure a good level of fabric performance from extensions.

Learn more about the Primary Energy Metric. 

3.    Little change for renovated elements

In contrast with the minimum requirements for new and replacement elements, the proposed standards for renovating existing thermal elements show only very minor changes. These apply where:

•    there is a change in use for the building (i.e. commercial to residential);
•    an existing fabric element becomes a thermal element (i.e. the roof for a loft conversion); and
•    a thermal element is renovated and has a higher U-value then the threshold value (shown in the table below).

In the proposals, threshold U-values are left unchanged and the only change for the minimum U-values is a marginal improvement for roof U-values.
Element type Threshold U-value (area weighted average) Current (L1B 2013) upgraded element (area weighted) Proposed 2021 upgraded element (area weighted)
All roof types 0.35 N/A 0.16
- Pitched roof 0.18
- Ceiling level 0.16
- Flat roof 0.18
Walls - cavity insulation 0.70 0.55 0.55
Walls - internal or external insulation 0.70 0.30 0.30
Floors 0.70 0.25 0.25

It is difficult to see how these proposals will align with the government’s commitment to raising ‘as many homes as possible to an EPC of C by 2035’. In practice, it may actually mean that the upgraded elements require further improvement in the future – creating additional disruption and cost for homeowners.

Whilst the consultation correctly notes issues which can occur through poorly conceived or installed insulation retrofits, such as increased condensation risk, it seems odd that its response to this is to target worse levels of fabric performance rather than seeking to raise industry practice. It would surely make more sense to use this update as an opportunity to engage with the whole house approach laid out within PAS 2035, including creating clear medium-term improvement plans which clearly identify and prioritise the scheduling and priority of energy improvements for a property.

Of course, not every home is appropriate for the same level of improvement. The new guidance notes that historic and traditional buildings should only have their energy efficiency improved to the extent that it does not risk the long-term deterioration of the building fabric or fittings. Again, greater alignment with the recommendations outlined in PAS 2035 is key to improving each home practicably and appropriately to the best extent that is possible for them.

The guidance also notes that new extensions to historic or traditional dwellings should comply fully with the standards of energy efficiency in the approved document unless there is a need to match the external appearance or character of the extension to that of the host building.

Learn more about PAS 2035 and the whole house approach.

This lack of engagement seems particularly odd as, as we’ll discuss in the next section, the proposals for Part F (ventilation) do show some engagement with PAS 2035. Ultimately, if we are to close the performance gap, ensuring retrofits are carried out to a clear, bespoke plan and that the project team have an adequate understanding of best practice will be essential. This should be driven through effective regulation.

4.    Guidance provided on ventilation

As mentioned, one area where the consultation does seem to deal with the whole house approach is in the proposed changes to Part F, which deals with ventilation. In addition to simplifying some of the guidance, the consultation also notes that changes to energy efficiency measures can impact ventilation levels within a home and should be taken into account as part of work.

It’s worth noting that with existing homes, existing provisions for ventilation may already be inadequate pre-works, so it is important that an assessment of ventilation provisions is always undertaken when carrying out energy efficiency work and that the provision is improved where identified as being necessary alongside works to improve energy efficiency.

To support installers, the new guidance identifies two approaches to ensure effective ventilation within a property:

1.    simplified method - Measures are categorised as having either a major or minor impact on ventilation levels. For example, fitting internal or external insulation to 50% or more of the external wall area is considered a major upgrade whilst renewing loft insulation is considered minor. Using a flow chart based on the total number of major and minor improvements, installers can then determine a way to meet the ventilation requirements; and

2.    seeking expert advice which may include air permeability testing or complying with the process contained within PAS 2035. 

This approach represents a more sensible step forward, helping to maintain healthy environments within refurbished homes.

Further Information
Learn more about Part L of the Building Regulations. 

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