Roof Decking 101: When to Replace and What It Actually Costs

We're halfway through tearing off your old shingles when you hear it:

"You've got some bad decking here."

Now your $12,000 roof replacement just became $14,500. What happened?

What Roof Decking Actually Is

Decking (also called sheathing) is the wood layer between your rafters and your shingles. It's what holds everything together.

In Richmond homes built before 1980, it's usually 1x6 or 1x8 wood planks with gaps between them.

From 1980-2000, it's typically 1/2" or 5/8" plywood.

After 2000, builders switched to OSB (oriented strand board) or occasionally still use plywood.

All of it does the same job: gives your shingles something to nail into and creates a solid surface for your roof.

Why Decking Rots (Especially in Virginia)

Humidity. That's the short answer.

Richmond's summers run 80-90% humidity. Your attic hits 140°F. That combination pulls moisture into the wood from below, while any small roof leaks add moisture from above.

Common causes we find:

Old roof leaks. Water got under the shingles, sat on the wood, rotted it over years. You might not have even noticed the leak inside — it was small enough to evaporate in your attic before dripping through the ceiling.

Poor attic ventilation. No ridge vents or blocked soffit vents mean humid air stays trapped in your attic. Wood in constant contact with humid air degrades faster.

Ice dams. Water backs up under shingles, soaks into decking, freezes and thaws repeatedly. The wood never fully dries out.

Improper valley installation. Valleys channel a lot of water. If they weren't installed right, water seeps under the edges and rots the decking along the valley line.

Plumbing vents. The flashing around vent pipes fails more often than any other roof penetration. Water drips directly onto the decking every time it rains.

In humid climates like ours, even a small ongoing leak will rot decking in 3-5 years.

How We Know It Needs Replacing

You can't see it until the old shingles come off.

That's why every roof replacement estimate includes language like "subject to decking inspection" or "rotten decking replaced at $X per sheet."

What we look for during tear-off:

Soft spots. Our guys walk the roof after removing shingles. If you can feel the deck flex or bounce under your weight, that section needs replacing.

Visible rot. Wood that's dark, crumbly, or has visible mold/fungus growing on it.

Nail pop-through. If nails from the old roof pushed through the decking easily, the wood's integrity is shot.

Water staining. Dark stains mean water was sitting there long enough to discolor the wood. Even if it feels solid now, it's compromised.

Sagging between rafters. Healthy decking stays rigid. Rotted decking sags like a hammock between the support beams.

Most Richmond homes built before 1990 need at least some decking replacement. We typically find issues in 60-70% of tear-offs.

Plywood vs. OSB: The Debate

Contractors argue about this constantly. Here's what actually matters:

Plywood

Pros:

• Holds up better when wet (dries out faster, less swelling)
• Slightly stronger nail-holding power
• Traditional choice, been used for 70+ years
• Preferred by insurance adjusters in some cases

Cons:

• Costs 20-30% more than OSB
• Can delaminate if cheap grades are used
• Harder to find in stock during busy season

Our take: Plywood is the better choice for Richmond's humid climate. The extra cost is worth it.

OSB

Pros:

• Cheaper ($15-20 per sheet vs. $22-28 for plywood)
• More consistent quality (no voids or gaps)
• Uses less old-growth timber (more sustainable)
• Meets all building codes when properly installed

Cons:

• Swells more when wet, takes longer to dry
• Edges are vulnerable to moisture damage
• Some manufacturers have inconsistent quality

Our take: OSB works fine if you're budget-constrained, but we default to plywood unless you specifically ask for OSB.

What We Actually Use

For most Richmond replacements, we install 1/2" CDX plywood. "CDX" means it's rated for exterior use with some exposure to moisture.

For metal roofs or high-end projects, we step up to 5/8" plywood for added strength.

Building code minimum is 3/8" for rafters 16" apart, but we won't install anything thinner than 1/2". It's a false economy.

What Decking Replacement Costs in Richmond

Straight numbers based on 2026 pricing:

Material cost (plywood): $22-28 per 4x8 sheet Material cost (OSB): $15-20 per sheet Labor to remove and replace: $40-60 per sheet (includes disposal)

One sheet covers 32 square feet.

Total cost per square foot of decking replaced: $4.50-6.50

Real Examples from Recent Jobs

Midlothian ranch (2025):

• Roof size: 2,000 sq ft
• Decking replaced: 18 sheets (576 sq ft)
• Material: 1/2" CDX plywood
• Cost: $1,480 additional
• Reason: Old leak around chimney, plus valley rot

Glen Allen colonial (2024):

• Roof size: 2,400 sq ft
• Decking replaced: 32 sheets (1,024 sq ft)
• Material: Mix of plywood and some ridge repairs
• Cost: $2,720 additional
• Reason: Inadequate attic ventilation, entire ridge line was soft

Short Pump two-story (2025):

• Roof size: 1,800 sq ft
• Decking replaced: 6 sheets (192 sq ft)
• Material: 1/2" plywood
• Cost: $720 additional
• Reason: Isolated leak near bathroom vent

Budget for at least $1,000-1,500 in potential decking replacement on any Richmond roof over 15 years old. Sometimes you get lucky. Often you don't.

The "Can We Just Leave It?" Question

No.

Installing new shingles over rotten decking is like putting new tires on a rusted-out frame. It'll fail quickly, void your warranty, and potentially cause more damage.

Manufacturer warranties require solid decking. GAF, Owens Corning, CertainTeed — all of them. If your decking fails and takes the shingles with it, they won't cover it.

Soft decking won't hold nails. Shingles blow off in the first windstorm. We've seen it happen.

It gets worse. Rot spreads. That one soft sheet today becomes three soft sheets in two years.

If we find rotten decking, we'll show you exactly where it is and why it needs replacing. We don't replace decking that doesn't need it — we show you the bad sections and leave the good ones alone.

Questions to Ask Your Contractor

Before signing a roof replacement contract:

"What's your price per sheet for decking replacement?" Should be $120-180 per sheet installed. Higher in the Fan or other tight-access areas. Lower in easy suburban locations.

"Do you use plywood or OSB?" Find out what's standard and what the upgrade cost is if you want plywood instead of OSB.

"How do you determine if decking needs replacing?" Red flag answer: "We can tell from the attic." You can't. Some issues only show up after tear-off.

"Is decking replacement included in your base price or extra?" Most contracts list it as extra because we can't see it until shingles come off. Fair. But the rate should be clearly stated upfront.

"What thickness do you install?" Should be minimum 1/2", preferably 5/8" for metal roofs or premium projects.

What Happens During Replacement

Once we identify bad decking during tear-off:

1. We stop the tear-off in that section
2. Take photos of the damage
3. Show you (or send photos if you're not home)
4. Get approval to proceed
5. Cut out and remove the damaged section
6. Install new plywood (or OSB per your preference)
7. Continue with the new roof installation

We don't surprise you with a final bill that's $3,000 higher than the estimate. You approve the additional work before we do it.

Richmond-Specific Issues

Henrico County: Requires building inspector to see decking before new roof goes on if more than 30% is being replaced. Plan for a one-day delay if that happens.

Chesterfield County: Same rule but the threshold is 25%.

Historic homes in The Fan: Often have 1x8 plank decking with gaps. Code requires either filling the gaps or installing plywood over the planks. That's an additional cost most homeowners don't expect. Figure $2-3 per square foot for plywood overlay.

Homes built 1960-1980: Often have the thinnest decking (3/8" in some cases). We usually recommend overlaying with 1/2" plywood rather than trying to remove and replace the original thin boards.

Bottom Line

Roof decking is the foundation of your new roof. Rot is common in Richmond because of our humidity. Budget for it.

When we find it, we'll show you. We'll give you the price before we replace it. And we'll use quality materials that'll last as long as your new shingles.

Want an honest assessment of your roof including likely decking issues? Call (804) 238-7837 or schedule a free inspection. We'll give you the real story before tear-off day.