Planning permission and building regulations approval are separate processes. [1] [2]
Start with coordinated technical information
Planning drawings show the proposed development, but the building regulations design needs sufficient construction information to demonstrate compliance. Structural calculations, sections and specifications should agree with one another and with the layout being built. An engineer's design may depend on investigations of the existing building and ground. [3]
For ordinary non-higher-risk work, the building control route can be through the local authority or a registered building control approver. Agree the application and inspection arrangements before starting. [4]
What will the design address?
The relevant checks commonly include:
- Structure: foundations, walls, roof, structural openings and the way loads reach the ground.
- Fire safety: escape arrangements, protection of structural elements and spread of fire near boundaries.
- Moisture and floors: damp protection and the treatment of the junction with the existing house.
- Ventilation and energy: the altered rooms, extraction, insulation, openings and building services.
- Drainage and installations: the new drainage layout and the applicable requirements for the services being altered.
The details depend on the work. Redbridge's extension guidance explains the range of building regulations considerations; the Approved Documents provide the relevant technical guidance for fire, ventilation and energy. [1] [5] [6] [7]
Do not assume that only the new footprint matters. Removing a separating door can affect the escape route, and opening a conservatory into the dwelling can change its energy treatment. [8] [7]
Inspections must happen at the useful stage
Agree who will notify building control. LABC identifies inspections of foundation excavations, floors and other construction before key details are concealed. A completed surface cannot necessarily demonstrate that the hidden work beneath it complies. [9]
Ask the contractor to keep the approved or agreed drawings available on site, record relevant changes and coordinate inspections with the programme. Where the ground or existing construction differs from assumptions, obtain revised technical advice before building over the issue. [3]
At completion, obtain the appropriate building control completion documentation and retain the supporting certificates and information. LABC notes the importance of completion evidence when the property is sold. [9]
What changes from 24 March 2027?
For ordinary non-higher-risk work, the 2026 regulatory changes take effect on 24 March 2027. Transitional protection generally requires the relevant building notice, initial notice or full-plans application before that date and qualifying commencement before 24 March 2028. The legal commencement test needs checking; a planning approval or an intention to start is not enough. [10]
The Future Homes Standard concerns new homes, but the published 2026 Approved Document L also contains sections for existing dwellings and extensions. Use the correct edition and provisions for the actual project rather than assuming every new-home requirement applies—or that none of the 2027 changes can affect an extension. [11] [10]
Further published fire-guidance change
Approved Document B has a further published change taking effect on 2 September 2029, removing national fire-resistance classifications from its guidance, subject to transitional arrangements. For work around that date, check the applicable edition and the evidence supporting the specified fire-protection system. [12]