Delaminated roof sheathing on a home inspection

What does delaminated roof sheathing mean on an inspection report?

It means the plywood or OSB (oriented strand board) under your shingles is coming apart in layers, usually from moisture. Ask the seller for a credit sized to a licensed roofer's written bid, with a price for each extra sheet. Roofing maker IKO says no one can know for sure how much decking has rot until the shingles come off, so the per-sheet price is what protects you. "Roof decking" and "roof sheathing" are the same boards.

Key takeaways

• One edition of the residential code bars a new layer of roofing over a water-soaked or deteriorated roof. Your building department can say which edition applies.
• The underlying leak gets fixed before new decking goes on. Ask for both in the same bid.
• One Illinois roofer says the whole deck needs replacing once more than 30 to 40% of it is damaged.

What causes delamination of roof sheathing?

Water, most of the time. IKO names leaks and condensation as the two most common causes of a rotting deck.

Condensation comes from the attic side. The Department of Energy's Building America Solution Center says repeated or long condensation "can cause serious structural damage." That damage includes rot, swelling and delamination of OSB and plywood. It happens when warm, moist house air escapes into a cold attic and condenses on the underside of the sheathing. If your report also flags the vents, see attic ventilation on an inspection report.

What are the signs of bad roof sheathing?

Start in the attic. The International Association of Certified Home Inspectors (InterNACHI) lists these:

• Water stains on the underside of the decking.
• Dark staining on the decking, rafters or trusses. InterNACHI says this means moisture has been there long enough to support mold or start decay.
• Rusty nails poking through the deck, a sign of a persistent moisture problem.
• Sagging decking.

On the surface, IKO adds wood that feels spongy or crumbles, and a musty smell. A roofer may suspect rot just by feeling the deck give underfoot. Your report should say where the inspector saw it. If it lists raised fasteners instead, see roof nail pops on an inspection report.

Is delaminated roof decking serious?

It can be. InterNACHI says sagging decking, cracked or split rafters and weak supports can hurt the roof's ability to shed water and "may indicate serious structural concerns." If your report says the deck sags or feels soft underfoot, get a licensed roofer up there before your deadline.

It also changes what the roof job costs. The residential code's reroofing rule, section R908.3.1.1, bars a new layer of roofing over a roof that is "water soaked or has deteriorated." Deteriorated here means no longer "adequate as a base for additional roofing." The linked version is Colorado's 2021 code, and your local building department can tell you which edition applies at your address.

MyHomePros says many roofers check the deck during tear-off and recommend replacement when boards are soft, buckled or delaminated. IKO adds that a small area wet for a short time may be left in place. Global Exterior Experts, a roofer in Aurora, Illinois, says the whole deck needs replacing once more than 30 to 40% of it is damaged.

Is it expensive to replace roof decking?

It depends on how many sheets are bad. MyHomePros says many contractors give a base quote, then charge per sheet or per square foot once the deck is exposed.

Kept prices every line of an inspection report for $79, usually under 4 hours, so your bids go to the lines that need them.

Say the roof is due for replacement and tear-off turns up 10 bad sheets. At ArchitectureCourses.org's range, that's $750 to $1,500 on top of the reroof (10 × $75 and 10 × $150). On the Chicago-area roofer's terms, two sheets are included and the other eight run $95 each, or $760. Fixing the leak or the attic moisture is extra.

Call a licensed roofing contractor now. Ask for a written bid that names the likely sheet count, the price per extra sheet, and the moisture fix. IKO says the roofer has to resolve the underlying leak first. How to get repair estimates during the inspection period covers ways to get that figure while your window is open. If you haven't had a roof-only look yet, roof inspection before buying covers what one includes.

What should I ask the seller for?

Write it as one line, with scope, trade and the bid behind it:

• Roof deck: replace delaminated plywood or OSB sheathing and correct the moisture source, licensed roofing contractor, amount per the contractor's written bid, extra sheets at the bid's per-sheet price.

Ask for the work done by a licensed contractor with receipts, or a credit sized to the bid. Put the line in your buyer repair request letter. What to ask for after a home inspection shows how it fits with the rest of your list.

What if the seller says no?

You can accept it, ask for a credit or price cut instead, or walk away. A few bad sheets with a bid behind them is a line to negotiate. A sagging deck on an old roof is a bigger unknown until the roofer has looked. When to walk away after a home inspection walks through that call. Your contract sets the deadline and your options if the seller refuses, so confirm them with your agent.

For the other roof lines on your report, see roof findings on an inspection report.

Can you replace roof sheathing from the inside?

A roofer may spot the damage from the attic, but IKO's repair works from the roof side. All the roofing above the damaged area comes off first, including shingles and underlayment. The roofer cuts out the bad wood so each new piece lands on a rafter, then fits new decking of the same thickness.

Will insurance replace roof decking?

Don't count on it for damage that built up over time. The Maryland Insurance Administration says homeowners policies typically cover losses that are "sudden and accidental," from perils such as wind and hail. It says repairing "damage due to wear and tear or deterioration of your roof over time generally will not be paid for by the insurance company." Your policy's wording decides it, so settle the deck in your repair request rather than planning on a claim.

If the roof deck is one line of many, upload your inspection report to Kept and put the roofer's bid next to a priced memo for the rest of your list.

Sources

• Building America Solution Center, Condensation Control in Attics and Roofs in Cold Weather
• InterNACHI, What Your Attic Reveals: The Truth About Your Roof's Hidden Health
• IKO, What is Wood Rot and When to Replace Roof Sheathing
• UpCodes, R908.3.1.1 Roof Recover Not Allowed
• Maryland Insurance Administration, Does homeowners insurance pay for the replacement of your roof?
• ArchitectureCourses.org, Replacing Roof Sheathing: What It Costs and When You Need It
• MyHomePros, How Much Does It Cost to Replace Roof Decking?
• HomeHero Roofing, What Is Roof Sheathing?
• Global Exterior Experts, Roof Deck Repair Guide