As a good guide I would say between 10% and 20% more, depending on the type, size and quality of the building. The bigger the building and the higher the spec then the less of an increase it will be to achieve certified PH standard. PH doesn’t limit you to using a particular building material or system so there are both cheap and expensive ways to get to the standard. Sometimes there is no cost increase in achieving the standard because the design has been simplified so it really depends on the design you have. We have projects using UdiFRONT and UdiTOP systems in a timber frame which cost the same as conventional builds because they were designed to be passivhaus buildings from the start, reducing the costs of the deisgn stage of the project. Contact us if you'd like to know more.