Are Passive Houses more expensive to build than traditional homes?

There isn't a precise answer to this questions. It depends. Typically you pay a premium of up to 10-15% for the higher quality build, but there are several examples of Passive Houses being built for the same cost as (and occasionally even less than) a traditional house. The good news is that costs are steadily coming down as the standard becomes more normalized worldwide and another big advantage is that the cost is usually offset by the massive reduction in energy bills, and the elimination of heavy mechanical heating and cooling units.