On Thursday, 13 September 2018 22:31:33 UTC+1, JimK wrote:

How long are these joists?
Is the lantern going mid span?

The joists are 3000mm (or thereabouts) in length, and of 170mm x 50mm C24 timber. The headers and trimmers around the mid-span lantern opening are tripled-up and bolted together. I am expecting deflection to be minimal.

Is all this by one building outfit?

Yes, there is just the one builder (bar the sub-contractor that applied the membrane coating) and he has constructed the shell - responsibility for the lantern, doors and all internal work now rests with me. I am a keen DIYer but I can't build walls and don't have the confidence for the knock-through and working with large steels hence why I got a builder in to do all that (doing the roof seemed more a natural fit for him and the completion of his work too).