The root ball of a tree is usually equal to the drip line. That is, if the leaves and branches of the tree canopy reach out 30 feet from the trunk, the roots will -- or will try to -- reach out the same distance. So if a tree is planted so close to the house that the branches overhang the roof, the roots will be doing their darndest to push that way too, exerting a lot of pressure on the foundation. Once the tree is cut down, this pressure will go away. Decomposing roots shouldn't cause much of a problem. Removing the trees will also help extend the life of the roof. We do inspections in Silver Spring; you're welcome to give our office a call.