Loose shingles are something that can cause a great deal of damage before being discovered. Usually caused by wind or hail, this is more common with asphalt shingles than wooden ones. Unfortunately, the first sign of this is when you see a big stain in the ceiling or water running down a wall.
There is nothing like walking into a room where this has happened. The first thought is a broken water pipe but, before you call the plumber, take a look at the roof. This will not only save you a plumber bill but will show you are a smart person who knows to not jump to an immediate conclusion.
For the sake of this article, we will assume the roof has asphalt shingles. When installed, asphalt sealant and nails are used to secure the shingles in place. This sealing makes the roofing one continuous sheet, which resists the uplift pressures of the wind and rain. When you are suddenly hit with dripping water, it is obvious that you have a problem.