Next I will provide Construction / Building Regulation compliant drawings for the proposals including submission to the Local Authority or an Approved Inspector. For Full Plans approval, which would allow you to start works on site and provide the detail for your builder to follow and provide you with a quotation for what’s involved on the build.
The local council would then take around 8 weeks to process whereas alternatively using an Approved inspector could generally speed up this process.
I would liaise with your chosen Structural Engineer (an Engineer can be suggested if required) and include the relevant structural information on the proposed drawings.
This would include for the construction elements of the build to include plumbing and any new drain connections only, in other words a white box for client fit out.