The Welsh Government published its final impact assessment for proposed changes to Parts L, F and O of the Building Regulations for residential buildings in April 20221. The assessment covers dwellings in Wales and appraises costs and benefits over a 70-year period, net of those that would be incurred under current regulations1.
The proposed changes are expected to result in a net present value benefit of £102.4m and a reduction in greenhouse gas emissions of 1.6 million tonnes of CO2 equivalent1. Total costs are given as £470.3m and total benefits as £572.7m, with new dwellings accounting for £371.3m of costs and £412.6m of benefits, and existing dwellings £98.3m of costs and £160.1m of benefits1. Familiarisation costs are estimated at £0.7m present value1.
For new dwellings, the Part L energy efficiency changes are estimated to produce additional capital, replacement and maintenance costs of £358.7m present value, reduced energy costs of £213.4m and increased social benefits of £172.1m, giving a net present value policy benefit of £26.9m1. The air tightness test requirement is estimated to cost £0.6m in additional capital, with energy savings of £0.1m and social benefits of £0.2m, a net present value policy cost of £0.3m1. Part O, on mitigating overheating, is estimated to add £11.74m in capital costs, reduce energy costs by £2.64m and produce social benefits of £23.63m, a net present value policy benefit of £14.94m1.
For existing dwellings, the Part L changes are estimated to produce additional capital and replacement costs of £97.5m present value, reduced energy costs of £44.5m and increased social benefits of £115.9m, a net present value policy benefit of £62.7m1. The Part F ventilation changes for existing dwellings are estimated to add £0.9m in capital costs, a net present value policy cost of £0.9m, with health benefits not monetised1.
On ventilation, the assessment states that the proposed policy change is for the size of background ventilators to be increased from 2500mm2 to 5000mm2 equivalent area in habitable rooms for mechanical extract ventilation (MEV) systems1. The analysis suggests an additional cost of £0.250m (£0.026m EANC)1. The benefit is described as improved air distribution in the home, leading to improved ventilation and indoor air quality, with associated health benefits, but these have not been monetised due to difficulties and uncertainty in quantification1.
| Measure | Net present value |
|---|---|
| Part L, new dwellings | £26.9m benefit |
| Air tightness tests, new dwellings | £0.3m cost |
| Part F, new dwellings | £0.250m cost |
| Part O, new dwellings | £14.94m benefit |
| Part L, existing dwellings | £62.7m benefit |
| Part F, existing dwellings | £0.9m cost |
The assessment sets the policy in the context of the Net Zero target by 2050 set by Wales in March 2021 under the Environment (Wales) Act 2016, with interim emissions targets and carbon budgets, and the climate emergency declared by the Senedd in April 20191.
"The proposed changes are expected to result in a net present value benefit of £102.4m and a reduction in Greenhouse gas emissions of 1.6 million tonnes of CO2 equivalent."
Why it matters for households
The changes covered by the assessment affect the fabric, ventilation and overheating performance of homes in Wales, and so bear on how much energy a home needs and how well it manages heat and air. For new homes, the Part L changes cover improved fabric, PV and wastewater heat recovery, alongside requirements for air tightness tests, self-regulating devices and the removal of fuel factors1. For existing homes, the elements considered include extensions, windows, doors, conservatories, conversions, Boiler Plus and self-regulating devices1. The assessment notes that requiring self-regulating devices is assumed not to add significant cost or benefit because all new homes are assumed to install them already1. On removing the fuel factors, analysis for the England Part L changes suggested no material cost difference between retaining or removing the fuel factor when complying with the Part L target, and this has been assumed to apply in Wales1. The ventilation changes for existing dwellings apply where energy efficiency measures are likely to significantly reduce the air permeability of the dwelling1.
What happens next
The assessment is dated April 2022 and titled as the final impact assessment for the changes to April 22 Part L, Part F and Part O1. No further dated steps are set out in the document.