The Building Safety Act 2022 introduced the most significant changes to Part L in a decade. Yet most homeowners do not realise that swapping a boiler or adding loft insulation triggers a legal duty to notify building control. The obligation sits not with the installer alone, the homeowner bears ultimate responsibility.
As Osborne Clarke reports, the question of whether building regulations apply to retrofitting UK homes is not a theoretical one, it has real consequences for the 29 million existing dwellings that need upgrading to meet net zero targets. The legal firm’s analysis highlights a patchwork of rules that catch many homeowners off guard.
What the regulations say
Part L of the Building Regulations covers the conservation of fuel and power. For existing homes, it applies when you “materially alter” the building fabric, adding insulation, replacing windows, or installing a new heating system. The key test is whether the work reduces the building’s energy performance. If it does, you must bring the whole element up to current standards.
Replace a gas boiler with an air-source heat pump? That is a controlled service. The heat pump must meet minimum efficiency standards, and the installer must be on a competent person scheme (like MCS or Gas Safe Register) or you need building control approval. The same goes for new double glazing: it must achieve a U-value of 1.4 W/m²K or lower in England and Wales, per the 2022 update.
But there is a catch. Many homeowners assume that because a product has a CE or UKCA mark, it is automatically compliant with building regulations. It is not. The mark confirms safety, not energy performance. The installer or homeowner must submit a building notice or use a registered competent person to self-certify the work.
Who qualifies, and who does not
The rules differ across the four UK nations. In Scotland, the Scottish Building Standards apply, with a slightly different set of notification triggers. Northern Ireland follows Part F of its own regulations. England and Wales share Part L, but Wales has separate guidance documents.
The practical effect for a homeowner in Birmingham is this: if you install a heat pump without MCS certification, your local authority’s building control department can serve a notice requiring you to undo the work or apply retrospectively. That retrospective application costs more, typically £200-£400 for a single installation, and can delay your project by weeks.
What this misses is the EPC impact. An unregistered heat pump or unapproved insulation may not be recorded on your Energy Performance Certificate. When you sell the house, the buyer’s solicitor will flag the discrepancy. The EPC rating could drop by one or two bands, which reduces the property’s marketability. The average cost of an EPC reassessment is £60-£120, but the delay to a sale can cost thousands.
What it costs a typical 3-bed semi
For a typical 3-bed semi in England, a full retrofit package, cavity wall insulation, loft insulation to 270 mm, double glazing, and an air-source heat pump, might cost £12,000-£18,000. Of that, compliance costs add roughly 5-15%: building control fees (£200-£500), certification from the competent person scheme (often included in the installation price but worth checking), and potential remedial work if the existing fabric is substandard.
Grants can help. The Boiler Upgrade Scheme offers £7,500 towards a heat pump, but only if the installer is MCS-certified and the work meets building regs. The Great British Insulation Scheme similarly requires compliance. If you skip the paperwork, you forfeit the grant and face enforcement action.
Ofgem figures show that around 15% of heat pump installations in 2023 failed initial compliance checks, mostly because of missing paperwork or unapproved installers. The cost of rectifying that after the fact, hiring a building control officer, paying for a structural survey, can exceed £1,000.
What to do and by when
Before any retrofit work begins, check with your local authority building control department whether the project requires notification. If you use a competent person scheme installer, ask for their registration number and verify it on the scheme’s website. Keep all certificates, they are proof of compliance for your EPC and future sale.
For major projects like a whole-house retrofit, consider using a building control body directly. They can provide a single application covering multiple works, which is often cheaper than separate notices. The application must be submitted before work starts, not after.
Deadlines: the Building Safety Act 2022 transitional provisions mean that projects started before 15 June 2023 may follow old rules, but anything after that date must comply with the 2022 updates. If you are planning a heat pump, the Boiler Upgrade Scheme closes to new applications on 31 March 2027. Apply early, the scheme has been oversubscribed in some regions.
Frequently Asked Questions
Yes, if you are adding more than 100 mm of insulation or changing the structure of the loft. Most reputable installers are on a competent person scheme and will self-certify the work. Check with your local authority if the installer does not provide certification.
The buyer's solicitor will ask for building regulation certificates. Without them, you may need to apply for a regularisation certificate or indemnity insurance, which can delay the sale by weeks and reduce the property's value. The EPC may also be downgraded, affecting the mortgage offer.
