Building Regulations vs Planning Permission: What's the Difference?

Planning permission controls whether a development is acceptable in terms of its impact on the surrounding area — its appearance, scale, use, and effect on neighbours and the local environment. It is administered by the Local Planning Authority (LPA), which is typically the district or borough council. In Hertfordshire, the relevant LPAs are Hertsmere Borough Council, Welwyn Hatfield Borough Council, St Albans City and District Council, Watford Borough Council, and Three Rivers District Council.

Building Regulations control how a building is constructed — its structural integrity, fire safety, thermal performance, sound insulation, drainage, electrical safety, and accessibility. They are administered by Building Control, which may be the local authority Building Control department or an approved inspector (a private sector alternative). Building Regulations apply regardless of whether planning permission is required.

The key distinction, as the Planning Portal (the UK government's official planning guidance resource) puts it, is that planning permission asks "should this be built?" while Building Regulations ask "how should this be built?" A project can have planning permission but fail to comply with Building Regulations — and vice versa. Both approvals are typically needed for a house extension, loft conversion, or new building.

A third approval — Permitted Development (PD) rights — allows certain types of development without requiring a planning application. PD rights are a form of pre-granted planning permission for specific, defined types of development. However, even where PD rights apply, Building Regulations approval is still required.

Planning permission is required when a development falls outside Permitted Development rights. For residential properties in England, PD rights allow a wide range of works without planning permission — including most rear extensions up to 4 metres deep (detached) or 3 metres deep (semi-detached/terraced), most loft conversions, most outbuildings, and most internal alterations.

Planning permission is required for: front extensions, side extensions that extend more than half the width of the original house, rear extensions that exceed the PD depth limits, changes of use (converting a house to flats, for example), new dwellings, and any development in a Conservation Area, Area of Outstanding Natural Beauty, or National Park that would otherwise be permitted development.

In Hertfordshire, Conservation Areas include parts of Radlett, Shenley, Borehamwood town centre, Elstree village, and several other settlements. Properties in these areas have restricted PD rights — even relatively minor works such as replacing windows, adding a satellite dish, or cladding an external wall require planning permission.

The planning application process involves submitting drawings, a design and access statement, and the application fee to the LPA. The LPA will consult neighbours and statutory consultees, assess the application against the Local Plan and national planning policy, and issue a decision within 8 weeks. Approximately 88% of householder planning applications in England are approved, according to MHCLG planning statistics.

Building Regulations approval is required for most structural building work — including extensions, loft conversions, garage conversions, new buildings, structural alterations, and certain electrical and plumbing work. The regulations are set out in the Building Regulations 2010 and the associated Approved Documents (A through to S), each covering a specific aspect of construction.

There are two routes to Building Regulations approval: a Full Plans application (where detailed drawings are submitted for approval before work starts — the recommended approach for extensions and loft conversions) and a Building Notice (where the builder notifies Building Control before starting work, without submitting detailed drawings — suitable for smaller projects). A third route, the Regularisation application, is available for work that has already been carried out without approval.

Building Control will inspect the work at key stages — typically the foundations, the damp-proof course, the structural frame, the roof structure, the insulation, and the completion. At the end of the project, Building Control issues a Completion Certificate, which confirms that the work complies with Building Regulations. This certificate is important for future property sales — mortgage lenders and conveyancers will ask for it.

Certain works are exempt from Building Regulations — including most repairs and maintenance, most internal alterations that don't affect structural elements or means of escape, and small detached buildings (under 15 m² floor area). However, even exempt works must be carried out to a reasonable standard.

Building without planning permission when it's required is a breach of planning control. The LPA can issue an enforcement notice requiring the unauthorised development to be demolished or altered to comply with planning requirements. There is a time limit on enforcement action — 4 years for operational development (building work) and 10 years for changes of use — but within those limits, the LPA can require demolition at the owner's expense.

Building without Building Regulations approval when it's required is a criminal offence. The local authority can prosecute the person who carried out the work (typically the builder) and issue a dangerous structure notice if the work poses a safety risk. More practically, the absence of a Completion Certificate will cause problems when you come to sell the property — solicitors acting for buyers will raise a requisition, and the buyer's mortgage lender may refuse to lend on a property with unauthorised building work.

The solution for historic unauthorised work is a Lawful Development Certificate (for planning) or a Regularisation application (for Building Regulations). Both involve a retrospective application to the relevant authority. Regularisation applications require the builder to open up the work for inspection — which may mean removing finishes to expose the structure — and to carry out any remedial work required to bring the construction up to standard.

Since 2013, the Neighbour Consultation Scheme (also known as the Prior Approval process) has allowed householders to build larger rear extensions under PD rights — up to 8 metres deep for detached houses and 6 metres deep for semi-detached and terraced houses — subject to a 42-day neighbour consultation period. If no objections are received, or if the LPA determines that the impact on neighbours is acceptable, Prior Approval is granted.

Prior Approval is not the same as planning permission — it's a lighter-touch process that only considers the impact on adjoining properties, not the full range of planning considerations. However, it does require a formal application to the LPA and a decision notice. Building Regulations approval is still required separately.

In Hertfordshire, the Prior Approval process is administered by the relevant LPA. The application fee is £120 (2025). The 42-day consultation period runs from the date the application is validated, not the date it's submitted.

TCM Building & Maintenance manages the full approvals process for all projects — from initial feasibility assessment through to the Completion Certificate. Our in-house architectural designers prepare the planning drawings and Building Regulations drawings, and our project managers liaise with the LPA and Building Control throughout the project.

For a client in St Albans who wanted to build a two-storey side and rear extension, our team identified that the project required a householder planning application (because the side extension exceeded the PD width limit) and a Full Plans Building Regulations application. We prepared both applications simultaneously, submitted them to St Albans City and District Council, and managed the consultation process. Planning permission was granted in 7 weeks; Building Regulations approval was granted in 4 weeks. The project completed on time and on budget, with the Completion Certificate issued within 2 weeks of practical completion.

Read our Building Regulations Guide for detailed technical information, or our House Extension Planning Guide for planning-specific advice.