How different is extending a house in the UK from Hong Kong?

First thing to know: the UK has two approvals, not one. Planning covers how it looks and the effect on your neighbours, and many small extensions count as Permitted Development, so there's no planning application. Building Regulations are a separate approval: safety and the technical side. In Hong Kong, if you touch the structure, you'd usually appoint an Authorized Person to submit plans, and the Buildings Department approves them before work starts.

Then the video goes part by part: A for structure (a steel beam), B for fire safety, L for energy efficiency, H for drainage, and the Party Wall Act.

Part B is a true story. While AI checked my drawings, it found that bedroom two's only window sat right above the new roof. I chose a protected stair for every room upstairs instead. Then an AI playing Building Control checked again, and found one more gap, at the store under the stairs.