Check the collar ties, the 2-by-4 or 2-by-6-inch boards that span from one bearing wall to the other. There should be one collar tie for each set of rafters. Collar ties prevent the walls from ...

Another hidden danger, according to Jeff Geary, a PM Homeowners Clinic contributor and an architect in Staten Island, N.Y., is a roof assembly from which collar ties have been removed.

Q: I purchased a piece of property that has a 150-year-old garage in bad shape. The roof sheathing is completely missing, but the rafters aren't rotted. I wonder whether I should tear it down and ...