Great to hear good feedback on a contractor.

If I want to install Sliding Aluminium Doors (+ Toughened Glass Juliette Balcony) instead of the specified French Doors in the Dormer of a Loft Conversion (Hip to Gable) for a 2m x 2.1 m opening, would i need any additional structural support for the doors? At the moment we have timber frame with beams top /bottom and 2 100x100 posts either side.

Why exactly do the loft conversion company think the design would not concur with Permitted Development rules? Are they drawing up plans for you? If not, it could get costly to apply for a Lawful Development Cert as you need plans for that. Under Permitted Development rulings for a dormer you would just need the calcs from the Structural Engineer and then your Building Regs. You don't need full on front, side elevation drawings etc of the whole house. That's my understanding. However, they do change the rules often, so I could be completely wrong.

I haven’t noticed a cold or draught from our velux windows in winter, but we have the white ones, not the wooden ones. I think in the summer you will absolutely need them to create a through flow of air. One of our veluxes is at the top of the stairs and it acts a bit like a chimney in venting hot air out in the summer. The other one creates a breeze across the bedroom. You will need to get a blackout blind, the velux ones are made to fit the window exactly and they’re very unobtrusive. They have a metallic backing, so presumably the little cushion of air between the blind and the window, doubled with the cold being reflected away by the metallic backing creates a little bit of extra insulation?