Building Regulations for Extensions: Approval and Sign-Off

Do you need building regulations approval for an extension?

Most extensions need approval under the building regulations, the Planning Portal says. Building regulations approval is different from planning permission, and you might need both, GOV.UK says, so an extension that needs no planning application under permitted development rights can still need it.

GOV.UK lists the extension of buildings among the work that needs approval, along with many alteration projects, such as installing a bathroom that involves plumbing, changing electrics near a bath or shower, replacing windows and doors, and installing or replacing a heating system.

What building regulations cover on an extension

The Planning Portal gives building regulations guidance on 13 areas of an extension, grouped here by the part of the build each one affects.

Part of the build	Areas the guidance covers
Structure	Foundations, walls below ground level, external walls, structural openings
Weather and energy	Roofs, doors and windows, energy efficiency
Services	Drainage, electrics, ventilation, kitchens and bathrooms
Internal	Flooring, internal walls

The Planning Portal’s guidance on load-bearing walls says a beam replacing one, for example to open the house into the extension, should be designed to carry the loads the wall was taking, normally with at least 150mm of bearing on each side, and a steel beam should normally have 30 minutes’ fire resistance.

Converting a garage, or part of one, into habitable space will normally need building regulations approval as well, the Planning Portal says.

Building control for an extension: full plans or a building notice

You can apply to your local council, through the Planning Portal, or to a private registered building control approver, GOV.UK’s guide to applying says. It sets out two routes for new work, and only the full plans route brings formal approval.

Route	How GOV.UK describes it	Periods
Full plans	The most thorough option	A decision within 5 weeks, or 2 months with your consent, then a completion certificate usually within 8 weeks of the building work being completed, as long as it complies
Building notice	Only smaller projects	Work can start 2 days after the notice is submitted, without the formal approval full plans brings

The wait for the certificate starts only once the building work is complete, so it comes on top of the time the build itself takes.

Agree who makes the application, and whether building control fees are in the price, before you accept a quote. Among the ten Nottingham builders we compare, Traditional Build project manages every build, including the plumbing and electrics, and Edge Building & Construction has structural engineers in its team.

Party wall notices for an extension

You also need to find out whether the work on your extension falls within the Party Wall etc. Act 1996, the Planning Portal says. The Act is separate from planning and building regulations control, and each type of work it covers needs notice to the neighbour before it starts, GOV.UK’s explanatory booklet says.

Work the Act covers	Notice before the work starts
Work to an existing party wall	At least 2 months
Building a new wall at or astride the boundary	At least 1 month
Excavating within 3 metres of a neighbour’s building or structure, deeper than its foundations	At least 1 month
Excavating within 6 metres, where the excavation meets a line drawn downwards at 45 degrees from the bottom of the neighbour’s foundations	At least 1 month

A notice is only valid for a year, the booklet says, and you wait out the notice period unless the neighbour agrees in writing to an earlier start. Work started without proper notice can be stopped by a court injunction.

If the neighbour has done nothing 14 days after the notice is served, a dispute is deemed to have arisen, the booklet says. One agreed surveyor, or one surveyor each, then draws up an award, and where there are two, they select a third. Where the work is solely for your benefit, you usually pay all the costs of the award, including the neighbour’s surveyor.

What happens if an extension does not comply

Building work has to comply with the building regulations whichever route you take, and GOV.UK’s approval guidance sets out what happens when it does not.

Work already carried out without consent after 11 November 1985 can be approved retrospectively through regularisation, which you apply for from a local authority building control body only, GOV.UK’s guide to applying says. You might need to make alterations before building control agrees the work complies and gives you a regularisation certificate.

The completion certificate and the paperwork to keep

The completion certificate is building control’s sign-off once the work complies. One from the building control body costs around £250 to £450, on Checkatrade’s figures for removing a load-bearing wall. Keep it with the rest of the extension’s paperwork for the day you sell.