Planning permission and building regulations are two separate approvals, and they need different drawings.
Planning drawings: what it looks like
Planning is about how the extension affects the street, the neighbours and the character of the area. The drawings show size, shape, position, windows and materials: existing and proposed floor plans, elevations, a roof plan, and a location and site plan.
Building regs drawings: how it's built
Building regulations are about safety and performance: structure, fire safety, insulation, ventilation, drainage and access. The drawings are technical, with sections, construction details and specification notes. They're what building control approves and what your builder prices from.
Structural calculations
If there's a steel beam, a new opening or a loft floor, building control needs calculations proving the structure works. Many firms send these to a separate engineer. At Ashbridge they're done in-house.
What it costs
For a single-storey extension: planning £650, building regs £850, both stages £1,350, or Complete with calculations £1,695. See all prices.