I have a car port under the end of the house, the supports for the house are conc. blockwork, L shaped (in section) piers with a 2" cavity containing Rockwool or similar insulation. The car port is being converted to domestic/internal room. BC says that original internal faces of car port piers need 50mm of insulation to achieve necessary u value, but I'd be happier just hiding them behind a standard 100 thick aerated Celcon/Thermalite wall (I don't mind losing the extra 50mm of space). I don't like stud walls and avoid them like the plague. Is this likely to be acceptable? Will 100mm aerated blocks boost the u value as much as 50mm Cellotex?