New Orleans sits in a subtropical climate zone where relative humidity averages 76 percent year-round and summer attic temperatures routinely exceed 140 degrees. That combination creates a constant cycle of moisture absorption and thermal expansion in roof sheathing. Plywood swells when humid air saturates the wood fibers, then contracts when the sun heats the roof surface. Over time, this cycle weakens the wood grain and causes warping. Add the weight of asphalt shingles and the stress from high wind events, and you get deflected roof sheathing that dips between rafters. Homes built before 2000 often used thinner plywood or wider rafter spacing, which makes them more vulnerable to sagging.
Louisiana Residential Building Code requires roof sheathing to be properly nailed to framing members and rated for the wind zone in Orleans Parish. Many older homes do not meet current standards, and insurance companies now require proof of code compliance before issuing or renewing wind coverage. Heritage Roofing understands these requirements and documents every repair to meet both city inspection standards and insurance underwriting criteria. We also know which neighborhoods have the highest risk for moisture damage due to proximity to Lake Pontchartrain or the Mississippi River, and we adjust our ventilation and moisture barrier strategies accordingly.