I have an external doorway in a pebble-dashed 9 inch brick wall which I would like to fill in. Would I have to comply with current insulation regulations for this short piece of wall or can I just fill in with 9 inch blocks and plaster and render afterwards??
sorry I must have been half asleep writing this, I didn't read your problem properly, it would best to build your doorway in thermalite but lay them flat. As your existing walls are 9 inches thick with no cavity then its pointless creating a cavity for the doorway