Hi. We are doing kitchen extension at the moment - had agreed with the builder that he'll be doing hollow walls, he has now changed his mind and said because the house is built of hollow block he has to use hollow blocks so the width of the walls matches and there is no "step in" i.e. the new and old wall joins rather than sticks out. He said he would put 100mm high density insulation on the inside and it will be higher than regulation requires. I heard hollow block walls are not great - do you think they could be made good with sufficient insulation as he suggests?