Revised domestic building standards – Part L Building Regulations

date Released On 12th May 2022

The new Part L of the 2021 Building Regulations takes effect in June 2022, with new dwellings required to produce 30% less CO2 than the standard for Part L of the 2013 Building Regulations.

DLUHC has provided an update to the 2019 impact assessment for the 2021 changes to Part L of the Building Regulations, with a Final Stage Impact Assessment published in December 2021.  This update considers the estimated costs of a 30% reduction in CO2 on 2013 levels.  Unlike the 2019 impact assessment, the 2021 assessment provides a clearer picture of the two likely routes that housebuilders will use to meet the new standards:

  • The impact assessment considers that the most likely means of compliance is a high level of energy efficiency, a gas boiler, solar panels (PV) and waste water heat recovery. This requires the least change from current building practices and for many housebuilders is the lowest cost solution in the short run.
  • The assessment considers that the main alternative route to compliance for housebuilders is with an air source heat pump (ASHP). This starts the transition to the Future Homes Standard and would also be suitable for areas that do not have a natural gas supply.

The updated costs are drawn from consultation with the development industry and reflect the immaturity of air source heat pump installation supply chains and procurement processes, as well as ongoing reductions in the variable costs of photovoltaic panel installation.  The impact assessment draws attention to the different relative costs of compliance by house types, and notes that while gas boiler and solar PV is the cheaper route for most dwelling types, the ASHP is the cheaper route for detached houses. This reflects the assumed existing provision of a hot water cylinder for detached houses while other dwelling types are assumed to have existing provision of combi boilers with no hot water cylinder.

The figures below are drawn from Table 8 in the 2021 Impact Assessment

Additional cost per dwelling over 2013 Building Regulations Gas boiler and Solar PV





















The impact assessment suggested that the average cost of compliance per dwelling for the gas boiler and solar PV route was £3,660 and £4,070 for the air source heat pump route[1].

Notably, the 2021 impact assessment estimates that the costs associated with both heat pumps and solar PV will fall[2], as supply chains mature and become more integrated, and learning rates take effect. The assessment suggests that the cost of a heat pump will be around 75% of the initial cost, whilst for Solar PV they will be around 83% of the cost – although the suggested timeframes are no more specific than “later years of the policy“.

While the impact assessment covers the immediate costs of the changes to Part L, it seems to us that the next set of costs for moving to net zero carbon emissions (Future Homes) are far from settled - although these can reasonably be expected to reduce as the industry increasingly gears up for new ways of building housing.   However, in the short term much will depend on the availability of relevant technology and appropriately trained installers. Either way, these are costs that can impact on development viability and while some adjustments to land value can be expected, trade-offs may be needed with other policy requirements in order to maintain delivery.

The full impact assessment link is: Impact Assessment (

1   Based on the impact assessment’s assumed dwelling mix and sizes

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