Roof decking — OSB vs plywood, APA grade-stamping, full-deck replacement triggers

Roof decking (also called sheathing) is the structural panel layer the underlayment, ice and water shield, and shingles attach to. Most modern Houston residential roofs use OSB (oriented strand board) — typically 7/16 inch or 19/32 inch thickness depending on rafter span — because OSB is significantly less expensive than plywood and meets the same span and load standards. Older homes and some premium new construction use plywood (typically CDX-grade), which costs more, holds nails slightly better at the panel edges, and has better long-term wet-and-dry-cycle resilience. Both materials are graded and stamped by the APA (the Engineered Wood Association); the stamp documents span rating, thickness, exposure rating, and grade. IRC Section R803 governs sheathing requirements and the fastening schedule that holds it to the rafters. Full-deck replacement is meaningfully more expensive than a re-roof on intact decking. The four conditions that typically trigger full or partial deck replacement are: visible delamination of the panel surface (an OSB-specific failure when the panel has cycled wet-dry repeatedly); soft spots underfoot when a roofer walks the existing roof during inspection (a structural sign of internal rot or weakened panel bonding); rot or moisture damage visible on the attic side of the deck (typically associated with chronic ventilation deficits or active leaks); and visible sag or wave in the roof line as seen from the ground (a sign of structural deflection or panel failure). The first three are professional-inspector judgments; the last is sometimes visible to a homeowner from the curb. A re-roof quote that ignores deck condition entirely is making an assumption that may not hold once the existing roof is off — most legitimate quotes treat deck replacement as a per-sheet line item priced by current lumber cost (cross-reference D9-008 for the cost-factor framing). Whether any specific roof's decking is sound is a qualified inspector's call, not a homeowner determination from the ground. [Source: IRC Section R803 roof sheathing; APA Engineered Wood Association panel grade-stamp reference; NRCA Roofing Manual deck preparation chapter; ASTM D5456 oriented strand board standard]