I'm having a problem with mold growing on the boards of the attic ceiling above the joists. I live in southwestern PA. and we have a lot of snow and cold weather. Temperatures have ranged from 40's to teens. The mold is both a black spot mold and a more intrusive green mold that is covering the entire surface of the inside of the roof. The nails are covered with frost and water is dripping from the nails when it gets warmer. I have a ridge vent, soffit vents that you can see the light through and two windows on either end of the attic. The roof is a hip roof with a 4/12 pitch. There is insulation on the floor of the attic between the ceilings of the bedrooms and the attic which is open to a covered floor walkway (8ft wide by 32 feet long) We got a new gas forced air furnace this summer with a humidifier and I seem to notice the green mold only after the installation of the furnace. Any advice that you could give me would be greatly appreciated.