As home inspectors in NJ we are very busy this time of year looking for effects of ice daming that wicks up into the roof sheathing. This condition occurs after trapped ice and snow begins to melt in the gutters and has no place to go except in. The space behind the gutter is open to the decking under your shingles.
Some roofs have rubberized type membranes installed along the starter course to impede the flow of water into the home. This does work.
Home inspectors have moisture meters to determine if stains are active.
Call us at 800-989-3872 or visit us on the web at www.pinnaclehomeinspections.com