Warben

I’m planning a single-storey rear extension with a basement underneath, and I’d love to hear from anyone with experience of something similar — particularly around costs (£/m²) and who to get involved. The rear of the property sits on a significant slope, so a retaining wall will be needed regardless. I’m in North Somerset, about 20 minutes from Bristol. The basement doesn’t need to be the same size as the basement. I’ve put a picture of the rear of the property below. The main reason for the basement is acoustic separation — I want to use the space as a music room (drums, electric guitar) along with a cinema room or gym. Being below ground should help keep the noise away from the rest of the house naturally. I’m keeping it single-storey partly because light is already a consideration on this plot, and I don’t want to affect the neighbours’ light either. The plan is to use rooflights to bring as much natural light into the extension as possible. So — who exactly needs to be involved (specific type of architect, structural engineer, specialist basement contractor?), and what are realistic cost expectations for this kind of build in the South West? I know basements aren’t everyone’s first suggestion, but I’m genuinely keen on the idea and would love to hear from people who’ve actually done something similar rather than just being talked out of it!