Sagging Roof Deck
in Raleigh, NC

Raleigh's long humid summers, where relative humidity regularly stays above 80% for weeks at a time, allow moisture to accumulate in poorly ventilated attic spaces and slowly rot OSB or plywood sheathing panels from the inside out. Homes built in the 1980s and early 1990s in neighborhoods like Cary and Apex frequently used OSB sheathing that is particularly sensitive to chronic moisture exposure, losing structural integrity long before surface damage becomes visible.

Wake County saw rapid housing construction through the 1970s and 1980s when some builders used rafter sizing at the minimum allowable span, leaving little margin for the additional dead loads of roof-mounted HVAC equipment, satellite dishes, or a second layer of shingles added at the first re-roof. Over time this chronic overloading causes mid-span rafter deflection, which pulls the sheathing down with it and creates the characteristic wavy roofline.

While Raleigh's winters are mild on average, the region experiences several freeze-thaw cycles each January and February where daytime temperatures climb above freezing and overnight temperatures drop into the mid-20s. This pattern allows snowmelt to refreeze at the cold eave overhang, backing water under shingles and into the sheathing edge, which is the most vulnerable panel zone and the first to delaminate and sag.