Welsh Government release Stage 2A Consultation - Part L and F Review

On 25th November 2020 the Welsh Government launched a new consultation on Part F and L of the building regulations. Following on from the stage 1 consultation covering Approved Documents (AD) F and L1A for new dwellings last year, the stage 2A consultation focusses on the energy efficiency and ventilation standards for Existing Dwellings (including new conversions and extensions), Non Domestic buildings, Mitigation of Overheating risk in New Dwellings and Transitional Arrangements. The consultation closes on 17th February 2021 and can be found here.

Elmhurst has analyzed the consultation in detail and can summarise the proposals as follows;

Part L standards for Conversions, Extensions and Renovations

Approved Document L1B covers work to existing dwellings. This includes creation of new extensions, conversion into dwellings and renovation of thermal elements. The changes proposed include:

  • In the last change to Part L1B in Wales, the limiting fabric parameters for new extensions were aligned with the standards for new dwellings. It is proposed to do the same again so the limiting fabric standards for new extensions would be the same as proposed in the consultation on L1A last year. The standards proposed are;

External Walls

0.18 W/m2K

Party Walls

0.2 W/m2K


0.15 W/m2K


0.13 W/m2K

Windows, roof windows, glazed roof lights, curtain walling, and pedestrian doors

1.4 W/m2K

  • It is proposed to lower the standard for replacement openings to 1.4 w/m2k (previously 1.6 w/m2k).
  • Retained pitched and flat roofs in conversions and renovations now have to achieve a u-value of 0.16 w/m2k (previously 0.18 w/m2k).
  • Where suitability of an upgrade needs to be assessed prior to additional of insulation, it is proposed the person carrying out this work should be appropriately trained in risk assessment and management, e.g. a Retrofit Coordinator as identified in PAS 2035, and follow the procedures given in PAS 2030/2035: 2019 - Retrofitting dwellings for improved energy efficiency: Specification and guidance.
  • Introduction of boiler plus legislation. Currently in force in England, this requires;
    • gas boilers to achieve an ErP efficiency of 92% or higher,
    • the use of timers and room thermostats
    • for gas combi boilers, either Flue Gas Heat Recovery, Weather/load compensation or smart controls must be used
  • To future proof systems to take low carbon heating, where a system is installed it should be sized to allow for a flow temperature of 55°C or lower.
  • Amend consequential improvements for extending or converting a building by more than 10 m2;
    • Remove guidance for adding further insulation in partially filled cavity walls due to moisture risk
    • The guidance for insulation of un-insulated cavity walls will include an independent assessment to ensure the wall is suitable for upgrading (e.g. suitable cavity width, sufficiently clean cavity, satisfactory wall tie type/condition, satisfactory mortar joints for sound weatherproofing). We propose to align with Path A (simple or single measures projects) of PAS 2035/2030: 20194. By aligning with PAS 2035 there is inherent assurance that the person carrying the assessment is competent to do so
  • Some changes to align with EPBD including the use of primary energy instead of carbon as a metric where more design flexibility is needed in conversions or extensions.


Part F standards for Existing Dwellings

  • A new section in Part F is proposed where energy efficiency upgrades are made to existing buildings. Two options are provided;
  • A simplified method is set out in the Approved Document. It specifies additional ventilation provisions for different energy efficiency retrofit scenarios. This method is intended to be appropriate for the majority of existing dwellings.
  • The Approved Document provides the alternative of expert advice. This may be followed if, for example, the simplified method is not appropriate.
  • To help control condensation and improve indoor air quality, the proposal now makes reasonable provision to include additional ventilation when replacing existing windows which either have no background ventilators, or where the size of the background ventilators in the existing window is not known.
  • New or replacement ventilation systems in a retrofit should be subject to the same requirements as in a new build dwelling in regards to commissioning and testing and results provided to building control.
  • Further guidance on background ventilator rates for when additional habitable rooms and refurbishing a kitchen or bathroom.

Mitigation of Overheating risk in New Dwellings

The assessment of overheating risk in new dwellings within SAP has often been criticised as not detailed enough, particularly for high risk scenarios such as inner city apartment blocks. Although the assessment of overheating risk currently sits in AD L1A, it was not part of the stage 1 consultation issued last year. Overheating buildings is a particular area of concern for the Welsh Government and this consultation proposes the following changes;

  • Creation of a new part of building regulations, Part S, to specifically look at overheating in all flats and only houses that do not have ‘cross ventilation’.
  • Proposes two alternative approaches to demonstrating compliance with Part S;
    • A simplified method which specifies prescriptive measures (window areas, shading etc.) and no additional modelling
    • A dynamic thermal analysis model using the CIBSE TM59 methodology
  • Concerns over noise pollution and safety to be dealt with by planning and other areas of building regulations respectively, so no new guidance in Part S.
  • Information must be given to owner about any systems used to prevent overheating.

This is a significant change and appears to take away the requirement to assess the risk of overheating in SAP.

Part L changes for Non Domestic Buildings

No significant changes here, some amendments in line with EPBD in regards to the following;

  • Self-regulating devices
  • Building automation and control systems
  • Technical building systems

The energy efficiency requirements for non domestic buildings as specified in AD L2A and L2B will be considered in a future consultation in early 2021.

Transitional Arrangements

The stage 1 consultation set out the intention for tightening of transitional arrangements. The responses received were supportive of this and therefore the stage 2A consultation sets out some more details around this subject.

Where a building notice, initial notice or full plans deposit has been submitted to the building control body before the 2021 Part L and Part S amendments come into force, we propose that the transitional arrangements should only apply to individual buildings on which building work has started within a reasonable period. We propose that a reasonable period for this purpose is the period of 2 years from the date the 2021 Part L and Part S amendments come into force

The reasonable period will be set at two years. Therefore if a regulations application is deposited before the next Part L and S starts, the building will have up to 2 years to start work otherwise they will need to be built to the new standards.

Also note this is applied to “individual buildings” – not on a site wide basis as before. The intention of this is to encourage dwellings to be built to the latest standards as much as possible and may see sites built out more quickly.

On Construction Team Leader Jason Hewins commented:

 “We applaud the Welsh Government for publishing this consultation which contains some important changes to the Part F and L regulations for both new and existing buildings. The change to overheating assessment is particularly significant for OCDEAs, and we imagine these proposals will be fairly similar in the long awaited consultation on AD L1B, L2 and overheating risk in England.

As with any consultation Elmhurst will now formulate a draft response and publish this for all to see our views. We will listen to our members feedback before submitting our final response next year. We encourage all members to respond to this important consultation before the February closing date.”

Article published: 08/12/2020

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