Steel portal frame class q walls and insulation?

[barnfield]

I know there's a few others who have done class q on steel portals I'm running in circles at the moment on walls and insulation. Existing form has block wall to be retained and steel frame and roof.

Think it will have to be a cold roof design and no external insulation due to external dimensions having to remain the same. I would like it well insulated as was hoping to heat with ASHP.

Had thought I'd build cavity wall with inner skin of blocks, fill with insulation. But now it seems steel portal frames aren't approved for cavity wall insulation. Also bit concerned about condensation as a separate issue. Any experience/advice? Thanks!

 

[Forever Fendt]

100mm timber stud inside your walls / steel frame sat on 2 course of bricks and dpc fill stud with 100mm insulation and tape joints with foil tape to act as a vapour barrier then fix plaster board with 15mm insulation backing over to avoid any cold bridging

 

[Billboy1]

How much would it cost roughly for a 2000 sq foot steel portal conversion, 3bed on one level with new roof and recycled walls etc ? I know it’s a bit of a piece of string question