Attic heat
From May to September, the sun loads a Piedmont roof all day — and an attic that cannot exhaust that heat turns into an oven under the shingles. The covering then ages from both sides at once: ultraviolet above, sustained heat below. It is the quietest reason Southern roofs retire years before their warranties suggest.
What heat does from below
Asphalt shingles are rated with functioning ventilation assumed. Bake them from underneath through five-month summers and the asphalt dries faster, the sealant strips age faster, and the whole covering moves through its life curve early — most visibly on south- and west-facing slopes that take the afternoon load. The same trapped heat runs up summer cooling costs, which is why an under-vented attic bills the household twice.
The tell-tales are readable: an upstairs that will not cool down on summer evenings, soffit vents blocked by insulation, a ridge with no exhaust at all — common on the region’s 1990s-2000s production housing, where builder-minimum ventilation met code and nothing more. Twenty summers later, that minimum has collected its debt from the shingles.
Replacement day is the cheap moment
Ventilation is intake at the eaves plus exhaust at the ridge, balanced. Correcting it as a retrofit means working around a finished roof; correcting it during replacement costs a fraction, because the deck is already open. It is the single scope line most often missing from the low bid — and the difference between the new covering reaching its rated life or repeating its predecessor’s early exit. Make every bidder name the intake and the exhaust; “we reinstall the vents” is not a ventilation scope.