Building regulations explained: what you need for an extension

Planning is about how a building looks; building regulations are about how it’s built. Here’s what approval involves, from drawings to the completion certificate.

Building regulations set minimum standards for structure, fire safety, insulation, ventilation, drainage and more. Almost every extension, loft conversion and structural alteration needs approval, even when planning permission doesn’t.

There are two main routes. A full plans application submits detailed drawings to building control before work starts, and they are checked and approved in advance. A building notice lets work begin sooner, with compliance checked on site as it goes. For extensions we usually recommend full plans: you know the design is approved before you’re committed, and quotes can be fixed against approved drawings.

• Detailed plans, sections and specifications
• Structural engineer’s calculations for beams, foundations and openings
• Insulation and thermal performance details
• Drainage, ventilation and fire safety information

Building control inspect the work at key stages, typically foundations, damp proof course, drainage, insulation and structure, and at completion. We book and manage these inspections as part of every project.

If your work affects a shared wall, or involves excavating close to a neighbour’s foundations, the Party Wall Act may apply. Notices need to be served before work starts: two months for work to a party wall and one month for nearby excavations. We make sure this is handled in good time so it doesn’t hold up the start date.