This is a frank discussion about proper attic and roof ventilation in order to prevent the onset of mold issues and shingle warranties in your properties. All modern construction should be code inspected to ensure that the proper ventilation was done at the time of construction, but, sadly, often doesn't due to inspections missing these critical observations. Older homes should be evaluated to ensure that proper ventilation is in place and working sufficiently, and the ventilation system(s) should be upgraded whenever there is going to be a probability of having new roof installations. Remember too, to pay attention to the chimney. Flashing can become loose over time, and there may be less obvious leaks related to the chimney. Mold must eat, and it feeds on moisture.