Mr. Declan Daly:

On cost optimum, there may be some confusion on the nearly zero energy building, NZEB, standards that one must achieve to get to B2. I do not want to get too technical, but the cost optimum refers to a certain detail. It is more a question of why spend €20,000 insulating a wall to a certain standard when it is a stone wall. When doing that, a certain acceptable construction detail must be met. Spending that much money might only save the homeowner €300, whereas spending half that sum could save him or her €200. That is cost optimum. How much money makes economic sense to put into a house? We might be chasing a B2 or A3 rating but we have to go back to asking what makes sense to do to the house. That is what is meant by cost optimum. It is not related to lowest tenders or price.