Hi, I'm building an extension and was wondering, can I build the internal leaf entirely of blocks. 7n below ground up to dpc and 3.5n above. Also do I need two course of blues on the inner leaf? I was thinking 9 course of blues outside (ground slopes away a tad and nearly all are visible) and two course of block internal with 3 course of blues if needed? Also are class b second blues ok to use? I'm using a rustic looking brick so chips won't matter as long as their water resistant is up to scratch. Thanks in advance