Full plans or building notice: which should you use?

The two routes side by side

For a horizontal extension, work counts as commenced once the foundations, any basement and the ground floor structure are complete (regulation 46A(3)). For other work, a full plans application has to say what the client considers to be 15% of the work, and that is the commencement point (14(1)(f)(vii) and 46A(4)).

When full plans is compulsory

(3) A person intending to carry out building work in relation to a building to which the Regulatory Reform (Fire Safety) Order 2005 applies, or will apply after the completion of the building work, shall give an application for building control approval with full plans. (4) A person intending to carry out building work which includes the erection of a building fronting onto a private street shall give an application for building control approval with full plans. (5) A person intending to carry out building work in relation to which paragraph H4 of Schedule 1 imposes a requirement shall give an application for building control approval with full plans.

A single house is outside the Fire Safety Order, which does not apply to domestic premises (article 6(1)(a)). A building with two or more flats is inside it for its structure, external walls and common parts (article 6(1A)), so work to a building containing flats, or a conversion that creates flats, is likely to need full plans: ask the council. Paragraph H4 applies to building work over a drain, sewer or disposal main shown on the sewerage undertaker's map, or work that could obstruct access to one. Check the sewer map before choosing a building notice for an extension.

The two-day rule

A person who proposes to carry out building work shall not start that work unless: (a) that person has given the relevant authority notice of intention to start work; and (b) at least two days have elapsed since the end of the day on which the notice was given.

This applies to both routes. It runs from the notice of intention to start, not from any approval, and a "day" in these regulations excludes Saturdays, Sundays and bank or public holidays (regulation 2). Give notice on Friday 2 October 2026 and the earliest start is Wednesday 7 October.

Five weeks, not "two months"

Regulation 14A(6) requires the council to notify you of its decision within five weeks of receiving the application, "or within such longer period as at any time the authority and the applicant agree in writing". There is no two-month ceiling in the regulation. That limit sat in section 16 of the Building Act 1984, which was omitted in England from 1 October 2023, but gov.uk still describes the decision as "within 5 weeks, or 2 months with your consent". A late decision is neither a grant nor a refusal (14A(7)). The council can also grant approval subject to modifications or further plans, but only with your written request or consent (14A(2) to (4)).

What each costs

Each council fixes its own charges in a charging scheme designed to recover its costs, taking one year with another (Building (Local Authority Charges) Regulations 2010, regulations 3 and 6(3)). A full plans application carries a plan charge, paid with the application, and an inspection charge, invoiced after the first inspection. A building notice carries one charge, paid when you give it (regulation 8(1)). A notice or application given without its charge is not valid (8(2)). VAT is added where it applies (8(1)(h)).

A worked example: Bristol City Council's charges from 1 April 2026 for an extension up to 40 m² are £700 including VAT for a building notice, and £700 for full plans if both charges are paid on submission. Paid in two stages, full plans costs £255 plus £480, £735 in total, because the staged fee includes an administration charge. On that scale the building notice is not the cheaper route.

What this means for you

A building notice suits small, simple work by a builder who knows the standards, where you accept that the council may ask for changes on site. Full plans suits extensions, loft conversions and structural alterations: the design can be checked before anyone prices or builds it, and the approval protects work built to it. If you want a private approver instead of the council, there is no building notice option: see council building control or a registered approver.

This guide covers England; Wales has its own versions of these provisions. Parallel Architecture prepares and coordinates the Building Regulations information for the projects it designs. Get in touch to talk a project through.