An older coastal house, 80.s vintage. Roof does not leak has always been painted. Was painted in darker colour previous to the new paint ironsand. After about 10 months, in some areas on roof, blistered were noted. They are predominantly around the hotter parts of the roof, on the sunny side. Also noticing blistering on the plastic down pipes. We paid a professional painter to do the work. We are wanting to know why it has blistered. There are hundreds of blisteres, as noted, in the more sunny aspect of the roof. T The roof is a metal New Zealand long run factory painted originally