Back to Blog Education Roof Decking Replacement: What's Under Your Shingles and Why It Matters
Mark WhiteSeptember 28, 20255 min read When we tear off your old shingles during a replacement, the first thing we inspect is the roof deck, the plywood or OSB (oriented strand board) sheets that your shingles are nailed into. This is the structural foundation of your entire roofing system, and it's hidden from view until tear-off day.
About 15-20% of roof replacements in San Antonio require some deck repair. Here's what we look for and what it costs.
OSB vs. Plywood: What's on Your Roof?
Homes built before the early 1990s typically have plywood decking (CDX grade). Plywood handles moisture exposure better, it swells but doesn't delaminate as quickly as OSB.
Homes built after the mid-1990s typically have OSB, which is cheaper and structurally equivalent when dry. The problem: OSB swells and delaminates when exposed to prolonged moisture. Once OSB gets wet and dries repeatedly, it never returns to its original strength.
This is why leak repair urgency matters more on OSB-deck homes. A small leak on plywood might cause minor swelling. The same leak on OSB can destroy a 4x8 sheet in a single rain season.
Signs Your Decking Needs Replacement
We assess every sheet of decking during tear-off. Replacement indicators include: soft or spongy spots when walked on, visible rot or delamination, dark water staining with compromised structural integrity, and gaps between sheets from swelling.
Most decking damage is localized, we replace individual sheets, not the entire deck. But if a roof has had years of unaddressed leaks, larger sections may need replacement.
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Individual sheet replacement: $75-$150 per 4x8 sheet (material and labor). Most roofs that need deck work require 2-8 sheets, adding $150-$1,200 to the project. Extensive deck replacement (10+ sheets): can add $1,000-$3,000.
This is a legitimate additional cost that can't be predicted until tear-off. Any roofer who guarantees 'no additional charges for decking' either hasn't looked at your roof or plans to install over rotting deck. Neither is acceptable.
Got a roofing question? Something keeping you up at night? (Besides that mysterious dripping sound?) Email me personally at mwhite@legacytx.com. I read and answer every single one.
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Owner, Legacy Home Improvements · San Antonio since 1999
Mark has been in the roofing business for over 25 years. He personally inspects homes, works with insurance adjusters, and answers every email at mwhite@legacytx.com.
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