The quiet half

Some problems announce themselves. The dangerous ones do not.

Everything under what is it doing starts because something broke and you noticed. These are the opposite. There is nothing to notice, nothing leaking and nothing making a noise, and the only way to know is to go and find out.

Each one is the same shape: whether it applies to your house, the cheap test that answers it, what the number means, and only then what it costs if the answer is bad.