I've come to the conclusion that 'breathable' paints are something of a con - the paints are inherently microporous, so the producers had to come up with a ploy as to why we should use the stuff. 'It's good for wood to breathe!', they say. I'm sorry, but the last thing exterior wood needs is to inhale and exhale water vapour. Years ago I was very pleased with a sash window I'd made, and painted with 'breathable' paint. It lasted two years before having to be completely stripped and sanded down. I then applied Butinox solvent-based paint (totally non-porous!), and that window, years later, is still as good today as the day I painted it. Same with my brother-in-law's double garage, wood-built and twelve years old, which has been painted twice with Butinox solvent-based wood-stain from new, and looks like it was put up yesterday. Water-based breathable paints have several advantages, not least their quick-drying properties. I use them indoors where, with central heating, the humidity tends to be low and fairly constant. But I would never use them for exterior work. Rant over! ;-)