So, my boyfriend (who is a builder who works for himself) is going to build me a gym in the garden. We have had to submit a planning application because its on the front elevation of the house. The planning application has been approved. Building Control are not interested in monitoring the building because its under 30m2. My boyfriend's brother is a structural engineer and has offered to do all the drawings, and can sign it off afterwards I think.
So, my question is, do I need to get a structural warranty (for the purposes of re-mortgaging or selling the house at a later date) on the building, even though its an outbuilding? Or can I rely on a Professional Consultant's Certificate from my boyfriend's brother?
All a bit new to this. Anyone had any experience?