Glossary
Architecture & planning glossary
Plain-English definitions of the terms that come up most often on a London home project, with links to the relevant services and guides.
- Article 4 direction
- A direction made by a local authority that removes specified permitted development rights in a defined area, meaning works that would otherwise be permitted require a planning application. Common in conservation areas.
- Planning ApplicationsConservation Area Architects
- Basement Impact Assessment
- A specialist report, required by many boroughs for basement projects, assessing the effect on ground conditions, hydrology, structure and neighbours.
- Basement ArchitectsLondon Basements: Process, Cost Drivers and Risks
- Biodiversity Net Gain (BNG)
- A requirement for many developments to deliver a measurable improvement in biodiversity of at least 10%, secured for at least 30 years. Householder home extensions are generally exempt under the de minimis exemption — development below 25m² that does not affect a priority habitat.
- Planning ApplicationsBiodiversity Net Gain and Home Extensions in London
- Build-over agreement
- The water authority’s agreement — in most of London, Thames Water — to build over or close to a public sewer. It is generally needed before construction where an extension sits near a public sewer, and it runs alongside, not instead of, building control.
- Building Regulations DrawingsBuilding Over a Public Sewer: Build-Over Agreements Explained
- Building control
- The process of checking that building work complies with the building regulations, carried out by local authority building control or a registered building control approver, via a full plans or building notice route.
- Building Regulations Drawings
- Building regulations
- The standards governing how building work is constructed — structure, fire safety, insulation, ventilation, drainage and more. Separate from planning permission, and usually required even when planning is not.
- Building Regulations DrawingsPlanning Drawings vs Building Regulations Drawings
- Community Infrastructure Levy (CIL)
- A charge some local authorities apply to new floorspace, calculated per square metre, to help fund infrastructure. Development that creates under 100m² of new floorspace is usually exempt as minor development, and extensions and annexes to a home you occupy can be relieved — but a new dwelling is always liable, and any exemption must be claimed before work starts or it is lost.
- Planning ApplicationsWill You Pay CIL on a London Extension?
- Conservation area
- An area designated for its special architectural or historic interest, where the local authority has extra control over change to preserve or enhance its character. Permitted development rights are often reduced.
- Conservation Area ArchitectsConservation Area Extensions and Consents in Hampstead
- Design and access statement
- A supporting document explaining the design rationale for a proposal, how it responds to context and policy, and how access works. Often required for larger or sensitive applications.
- Planning ApplicationsHeritage & Design Access Statements
- Designated land
- Land where permitted development rights are more restricted — conservation areas, National Parks, Areas of Outstanding Natural Beauty and World Heritage Sites. On such land, side extensions and some roof and cladding works are excluded, and the larger permitted-development routes are limited.
- Conservation Area ArchitectsPermitted Development Explained for London Houses
- Dropped kerb (vehicle crossover)
- A lowered section of kerb that lets a vehicle cross the footway into an off-street parking space, which needs the highway authority’s consent. Forming a crossover, and paving over a front garden, can also require planning permission depending on the surface used and whether the property is on designated land.
- Planning ApplicationsPaving a Front Garden and Dropped Kerbs: The Planning Rules
- Heritage statement
- A document explaining a building’s significance and how a proposal affects it, used to support listed building and many conservation-area applications.
- Heritage & Design Access Statements
- House in Multiple Occupation (HMO)
- A property occupied by several unrelated people who share facilities such as a kitchen or bathroom. A small HMO for three to six occupiers falls in use class C4; changing a single dwelling (C3) to C4 can be permitted development, but an Article 4 direction — in force across many London boroughs — removes that right so planning permission is required. Larger HMOs are sui generis.
- Planning ApplicationsChange of Use for Homeowners: Working From Home, HMOs and Short Lets
- Householder application
- A planning application for works to a single house, such as most extensions and alterations. It has a statutory target determination period of around eight weeks.
- Planning ApplicationsCamden Planning Permission for a Home Extension
- Lawful development certificate
- A formal confirmation from the local authority that proposed works would be lawful as permitted development, or that existing works are lawful. Useful for certainty and for a future sale or refinance.
- Lawful Development Certificates
- Licence to Alter
- A freeholder’s formal consent to alterations that a lease would otherwise restrict, usually documented by the freeholder’s solicitor and relying on drawings and technical information.
- Licence to Alter PackagesEstate, Trust & Freeholder ConsentsLicence to Alter Drawings for London Flats
- Listed building
- A building protected for its special architectural or historic interest. The protection covers the whole building, inside and out, so many alterations require listed building consent. Unauthorised works are a criminal offence.
- Listed Building ArchitectsListed Building ConsentListed Building Consent: A Guide for London Homeowners
- Listed building consent
- The consent required for works that affect the special interest of a listed building, separate from planning permission. A project may need both.
- Listed Building ConsentListed Building Consent: A Guide for London Homeowners
- Measured survey
- An accurate record of the existing building — plans, elevations, sections and levels — providing the reliable base for design, planning drawings and lease plans.
- Residential Architects
- Party wall award
- The document a party wall surveyor (or the two neighbours’ surveyors) prepares under the Party Wall etc. Act 1996 when a neighbour dissents from notified works. It sets out how and when the work may proceed and records the condition of the neighbouring property beforehand.
- Building Regulations DrawingsThe Party Wall Act Explained for London Homeowners
- Party Wall etc. Act 1996
- Legislation governing works to shared walls, works at the boundary, and excavation near a neighbour’s foundations. Where it applies, notices must be served and, if neighbours dissent, a party wall surveyor produces an award.
- Building Regulations DrawingsThe Party Wall Act Explained for London Homeowners
- Permitted development
- A national grant of planning permission allowing certain works to houses to proceed without a full planning application, subject to limits and conditions. It does not apply to flats and is frequently restricted in conservation areas and by Article 4 directions.
- Planning ApplicationsLawful Development CertificatesPermitted Development Explained for London Houses
- Planning condition
- A requirement attached to a planning permission. Some conditions must be discharged (approved) before work can start — pre-commencement conditions — and ignoring them can make works unauthorised.
- Planning ApplicationsPlanning Conditions Explained: After You Get Permission
- Pre-application advice
- A paid service from the local authority that tests the principle of a proposal before a full application, indicating the likely officer view. It is not binding but can reduce risk on sensitive schemes.
- Pre-Application Advice
- Principal Designer (CDM)
- A role under the Construction (Design and Management) Regulations 2015 that coordinates health and safety during the design phase of construction work involving more than one contractor.
- Construction Stage SupportPrincipal Designer Duties for Domestic Projects
- Prior approval
- A lighter-touch permitted-development procedure for certain works — notably the larger single-storey rear extension (up to 6m deep on a terraced or semi-detached house, 8m on a detached house) — where you must notify the council and give neighbours a chance to comment before building, so the council can consider the impact. It is not available in conservation areas or where the rights have been removed.
- Planning ApplicationsLawful Development CertificatesRear Extensions: Permitted Development and the Prior Approval Route
- RIBA Plan of Work
- The industry framework that organises a project into stages — from strategic definition and briefing through design and technical work to construction and handover.
- Full Architectural Service
- Section 106 agreement
- A planning obligation entered into under section 106 of the Town and Country Planning Act 1990 that makes a development acceptable in planning terms — for example securing affordable housing or financial contributions. It is more common on larger schemes than on single-home projects.
- Planning Applications
- Section 211 notice
- The formal notice you must give the council before carrying out work to most trees above a small trunk size in a conservation area, even where no Tree Preservation Order applies. It allows a statutory period — six weeks — during which the council can decide whether to protect the tree.
- Conservation Area ArchitectsTrees, TPOs and Conservation Areas: What You Can and Cannot Do
- Sui generis
- A use that falls outside the standard use classes — literally “of its own kind” — such as a large HMO, a pub or a theatre. Because it belongs to no class, a change to or from a sui generis use generally needs planning permission.
- Planning ApplicationsChange of Use for Homeowners: Working From Home, HMOs and Short Lets
- Tender package
- A coordinated set of drawings, schedules and an outline specification issued to contractors so they price the same scope on a consistent, comparable basis.
- Technical Design & Tender DocumentationChoosing and Working With a Builder in London
- Tree Preservation Order (TPO)
- An order protecting specified trees or woodland, making it an offence to cut down, top, lop, uproot or wilfully damage them without the council’s consent. A TPO can apply whether or not the property is in a conservation area.
- Conservation Area ArchitectsTrees, TPOs and Conservation Areas: What You Can and Cannot Do
- Use class
- The category the planning system assigns to how a building or land is used — for example C3, a dwellinghouse. Changing between some classes needs planning permission, while some changes are permitted development. The use classes in England were significantly reorganised in 2020.
- Planning ApplicationsChange of Use for Homeowners: Working From Home, HMOs and Short Lets
Have a question about a term?
If something here is unclear for your situation, send us the property details and we will explain what it means for your project.