I have a roof that has been sagging for several years now in Long Island, NY. It was put on now 20 years ago and the main beam running from one side of the house to a rock fireplace (that the rafters are attached to) is sagging in the middle. The guy who built it nailed 2X12's together to cover the 20 feet plus span but now it's dipping down in the middle almost 6inches below the ends. The sheetrock inside is buckling and the fake wooden beams he attached have already fallen down once. There is also little pitch to this roof which has caused leaks in the winter time when ice flows back up. To fix it I'm thinking of tearing out the main beam and replacing with a microlamb beam and then building new trusts off of and above the old ones to create a better pitch. My hope is that the microlamb can carry the new load and the change of pitch will solve the leaks where the two roofs meet. As I raise the hight of the roof with the new trusts I will get closer to the top of the chimney. Is there a certain clearance to consider? Also, the roof on some of the house is getting covered with moss and fungus. I've changed some roof parts with new shingles but it seems to be spreading to the other parts of the roof. When I re-roof is there a special shingle that will keep this from happening? Thanks in advance - I know there's a lot tide up in this one post.