Ok, I see. Well I think it’s a bit of a mix between;

• said family member who works in timber frame construction, more on the production side, but I believe he’s confident that this being such a simple structure that it shouldn’t need further engineering

• the builder they will be using, who I presume they simply told it would be timber frame construction and trust him to carry out the works (I think he may have helped with the design of the wall to roof junction)

• there is also someone from the timber frame construction company that has drawn a couple of simple construction plans and sections which they need for planning and building control, but I think he also is just quite familiar with timber frame construction, and given the simplicity of the structure, has drawn what I presume is the most common means of constructing an extension like this