Groundwork

Striking a buried cable or gas main can kill someone and land you with a five-figure bill. The safe version is nearly free: a desktop search plus an on-site scan before anyone digs.

Setting out transfers the approved drawings onto the ground before the dig. A near-free half-day that decides whether your foundations land in the right place.

How much spoil an extension dig really generates, why bulking catches people out, what muck away costs by the grab load, and the duty-of-care paperwork that legally follows your waste off site.

What type of foundations your extension needs, how deep they go, what they cost, and what to expect on dig day.

Foul and surface water drainage for your extension: what connects where, gradient rules, build-over agreements, soakaway requirements, and what building control inspects before backfilling.

Your BCO must inspect open foundation trenches before concrete is poured. Here's what they check, what 'bottoming up' means, and how to prepare so nothing delays the pour.

What an extension floor is actually made of, layer by layer, and what each layer costs. Ground-bearing vs suspended, the £1,500 – £3,000 build-up, and the one detail that causes damp.

Two BCO inspections stand between your foundations and the floor slab. Here's what the inspector checks at the drainage and oversite stages, how to prepare, and what happens if you cover the work too early.

Why the DPC matters, how it connects to your existing house, and the common mistakes that cause damp problems later.

Most UK extensions need no radon measures at all. How to check your postcode, the basic vs full protection decision, the sump, and what it costs (£100 – £250).