Back to Blog Roof Repair Roof Decking Damage in San Antonio: What It Is, What Causes It, and What It Costs to Fix
Mark WhiteJuly 1, 20266 min read When most people think about their roof, they think about the shingles. The visible layer. The part that looks good or doesn't. But underneath those shingles is the decking (also called sheathing), and it's the structural backbone of your entire roof system.
Roof decking is the layer of plywood or OSB (oriented strand board) nailed to your rafters. Everything else, the underlayment, the shingles, the flashing, is attached to it. When decking fails, nothing above it matters. And in San Antonio, decking damage is more common than most homeowners realize.
What Causes Decking Damage
The usual suspects in San Antonio:
- Water intrusion: The number one cause. A small leak that goes undetected for months or years gradually saturates the wood. By the time you see a ceiling stain, the decking may already be rotting.
- Poor ventilation: A hot, humid attic turns your decking into a moisture trap. Condensation on the underside of the decking leads to mold, fungal growth, and structural weakening over time.
- Age: OSB and plywood have finite lifespans. In San Antonio's climate, 25 to 35 years is typical before the wood starts losing structural integrity.
- Storm damage: Hail can dent decking through the shingles. Fallen tree limbs can crack or puncture it. And wind-driven rain during severe storms can force water under the shingles and saturate the wood.
- Improper repairs: Previous roofers who layered new shingles over old ones (a practice called an overlay) can trap moisture between layers, accelerating decking deterioration.
How to Spot Decking Problems
From outside:
- Sagging or wavy roof lines (the roof should be straight and flat between the ridgeline and eaves)
- Soft or spongy spots when walking on the roof (which is why homeowners shouldn't walk on their roofs, but a professional will check this)
- Visible dips or depressions in the roof surface
From inside the attic:
- Daylight visible through the decking boards
- Water stains or dark spots on the underside of the decking
- Mold or mildew on the wood surface
- Decking that feels soft or crumbly when pressed
- Musty or moldy smell
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Most San Antonio homes built after the mid-1990s use OSB (oriented strand board). It's cheaper than plywood and structurally adequate. However, OSB is more vulnerable to moisture damage. Once OSB gets wet, it swells and doesn't return to its original shape. The edges puff up, the layers delaminate, and structural strength drops quickly.
Plywood handles moisture better. It can get wet, dry out, and retain most of its strength. Older San Antonio homes often have plywood decking, which is one reason those roofs sometimes outlast their expected lifespan.
When we replace decking, we use the same type that's already there unless the homeowner opts to upgrade. Upgrading from OSB to plywood during a reroof is possible but costs about 15 to 20% more for materials.
What Decking Replacement Costs
During a roof replacement, we discover decking damage after the old shingles come off. Most roofing proposals include a price for decking replacement per sheet (a standard sheet is 4'x8').
Typical costs in San Antonio:
- Per sheet replacement (OSB): $75 to $125 per sheet installed
- Per sheet replacement (plywood): $90 to $150 per sheet installed
- Average roof needing decking work: 3 to 10 sheets (most replacements)
- Severe damage (full re-decking): $3,000 to $8,000+ depending on roof size
Here's the important thing: you usually don't know how much decking work you need until the old roof comes off. A good contractor will give you a per-sheet price upfront, inspect the decking thoroughly during the tear-off, and show you any damage before replacing it. No surprises, no inflated counts. If the decking is solid, you don't pay for decking work.
We always invite homeowners to be present during tear-off so they can see the decking condition firsthand. Transparency on decking is one of the biggest trust factors between a homeowner and their roofer.
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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