First you needs to open up the area a bit so the air can dry things out....this may mean trimming a few trees. Also try and get the sun light on the roof a little more....the basic line is that you need to dry out your roof and this will take care of the problem. This may sound nuts....but if you don't want to cut the limbs off your trees then you can mound a fan up in one near the house to keep things dry....we do this on the golf course industry all the time and it works good.