Hi I originally planned on building my new house in timber frame and have the house up to floor level. My question is can I now change to concrete block construction. The internal walls are in 4" block and all brought to floor level. I am thinking of putting in a hollow core floor to the 1st floor. Is this possible? At the moment The external wall is a block on the flat on the internal side and 4" on the outside. What is the best form of insulation to use?