Short answer
Roof decking is the plywood or plank sheathing under your shingles, and it gets replaced when it is soft, delaminated or broken so it will no longer hold a nail. It is almost always found after the old roof is stripped, which is why the per-sheet price needs to be settled in writing before work starts. Lightning Construction finds decking problems at the free inspection and prices them into the estimate, so there is no change order on the day.
On this page
- What roof decking is on a New Jersey house
- What rotted roof decking actually looks like
- Why it is only found after the tear-off
- Where decking rots first
- What the crew does when they find bad decking
- What decking replacement costs, and how to keep it from being a surprise
- The permit and the inspection
- What to do next
Roof decking is the layer of wood the shingles are nailed to. On most New Jersey houses it is either plywood or OSB sheets, or older solid boards running across the rafters. When that wood goes soft, splits or comes apart in layers, it stops holding fasteners, and no shingle installed over it will stay put.
Decking replacement is the single most common item that shows up mid-job on a roof replacement. Here is what it actually is, what bad wood looks like, and how to make sure it does not turn into a number you never agreed to.
What roof decking is on a New Jersey house
What you have under your shingles depends mostly on when the house was framed.
| Plank decking | Plywood or OSB | |
|---|---|---|
| Typical era | Plank deckingOlder housing stock, roughly pre-1960 | Plywood or OSBPost-war and later construction |
| What it looks like | Plank decking1x6 or 1x8 boards laid across the rafters with gaps | Plywood or OSB4x8 sheets with visible seams and H-clips |
| Common problems | Plank deckingCupped, split or cracked boards, gaps too wide to nail into reliably | Plywood or OSBDelamination, swelling at the seams, soft spots around penetrations |
| How it gets fixed | Plank deckingBad boards pulled and replaced, or the whole plane sheathed over with plywood | Plywood or OSBBad sheets cut out and replaced one for one |
Older cities in the state are full of plank roofs. Passaic, in Passaic County, has a median home built year of 1938. Trenton, in Mercer County, is 1953. Paterson is 1954. On houses of that age, it is normal to open a roof and find original boards, sometimes with three or four generations of nail holes in them.
None of that is bad news by itself. Plank decking that is dry, tight and sound gets reused. It is only replaced when it will no longer do its job.
What rotted roof decking actually looks like
From the driveway, you usually see nothing. From on top of the stripped roof, it is obvious.
- Dark staining. Water travels, so a stain is wider than the leak that made it. Gray or black discoloration across a sheet means moisture has been sitting there for seasons.
- Softness underfoot. A roofer walks the deck after tear-off. Sound plywood feels solid. Bad plywood flexes, and in the worst cases a boot goes partway through it.
- Delamination. Plywood is glued layers. When water gets in, the layers separate and the sheet peels apart at the edges. It looks fine from above and comes apart in your hand.
- Swollen seams. OSB that got wet swells at the edges and stays swollen, leaving a raised ridge that telegraphs through new shingles.
- Nails that will not hold. A fastener that spins, sinks past the surface, or pulls straight back out is the practical test. If the deck will not hold a nail, it is done.
- Daylight from the attic. Pinholes of light along a seam or around a chimney mean the sheathing has opened up.
Why it is only found after the tear-off
Shingles cover the decking completely. Nobody can see the wood until the old roof comes off, and no honest contractor will tell you otherwise.
What a good inspection does is narrow it down before the crew ever shows up. That means going into the attic with a light and looking at the underside of the sheathing, checking for staining around the chimney, the vent stacks and the valleys, pressing on suspect areas, and reading the roof from above for sagging between rafters and for shingles that have gone spongy.
That is the difference between an estimate written from the ground in ten minutes and one written after somebody got in the attic. The first one guarantees a surprise. The second one usually does not.
Where decking rots first
Rot is not random. It shows up in the same handful of places on almost every house.
Along the eaves. This is the most common spot in New Jersey. Ice backs up at the roof edge in winter, water works under the shingles, and the first three feet of decking absorbs it year after year. The ice dam guide covers why that happens and how to stop it.
In the valleys. Everything that lands on two roof planes ends up in one channel. If the valley flashing is old or was installed short, the decking under it takes the water.
Around chimneys and skylights. Failed step flashing and counterflashing leak slowly, and the wood immediately behind the chimney is often the worst on the roof.
Around vent pipes. The rubber boot on a plumbing stack cracks long before the shingles wear out. The rot is a neat circle around the pipe.
Anywhere the attic is not ventilated. This one is the whole roof at once. Warm, moist air with nowhere to go condenses on the cold underside of the sheathing all winter, and the deck rots from below with no leak anywhere. That is covered in the attic ventilation guide, and it is worth reading if your plywood is failing without an obvious water source.
What the crew does when they find bad decking
- Strip the section down to bare wood. The decking is not evaluated until the shingles, underlayment and old nails are off it.
- Sound it out. The crew walks and presses the deck to find every soft area, not only the visibly stained one.
- Mark and cut. Bad plywood is cut back to the center of a rafter on each side so the new sheet has something to fasten to. Bad planks are pulled whole.
- Install new sheathing of matching thickness. The new material has to sit flush with what is around it or the transition shows through the shingles.
- Fasten to the framing. Nailed or screwed into the rafters, with the correct gap at the sheet edges for expansion.
- Cover it the same day. Underlayment goes over the repaired area as the crew moves across the roof, so the deck is never left open overnight.
Sound decking is left alone. There is no reason to replace wood that is doing its job, and a contractor who wants to re-sheathe an entire sound roof should be able to tell you exactly why.
What decking replacement costs, and how to keep it from being a surprise
The honest answer on cost is that decking is priced per sheet or per board, and the number varies with the material and how much of it there is. What matters far more than the rate is when you agree to it.
There are two ways this goes:
- The contract says decking is billed as found, at a rate nobody discussed. The old roof comes off, you get a phone call, and you have no leverage because your house is open.
- The rate is written into the contract before anybody starts, or the decking is inspected and priced into the total up front.
Lightning Construction works the second way, and takes it further. There are no change orders. The written estimate is the final price, and the conditions that normally trigger one — extra shingle layers, damaged decking, inadequate flashing — are identified at the free inspection and included in the quote. There is also no deposit; nothing is due until the work is finished and you have inspected it.
For the overall job, most asphalt roof replacements run $9,000 to $22,000 in standard-value towns, $14,000 to $35,000 in higher-value towns, and $25,000 to $60,000 for large or luxury homes. The band is set by the municipality's median home value from ACS 2024 five-year estimates. The New Jersey roof cost guide breaks down what pushes a job from one end of a band to the other.
If you are getting other quotes, ask each contractor one question in writing: what is your per-sheet price for decking replacement, and is it in this contract? A contractor who will not put a number on it before the tear-off is telling you something.
The permit and the inspection
Roof work in New Jersey is done under the New Jersey Uniform Construction Code, and the municipal inspector may want to see the deck condition and the fastening. Lightning pulls the permit from the municipality's own construction office and attends the inspection, in every one of the 544 municipalities it serves. The homeowner files nothing.
That matters more than it sounds on a job with decking work in it, because the sheathing is the part an inspector will actually ask about.
What to do next
If you have stains on an attic rafter, a soft patch you can feel from the roof, or shingles that give under your foot, the decking is the thing to have looked at — not the shingles. Replacing shingles over a bad deck buys you nothing.
Lightning Construction is veteran-owned, GAF Certified, licensed and insured under New Jersey Home Improvement Contractor registration 13VH12437000, and rated 4.9 out of 5 from 264 Google reviews. Inspections and written estimates are free with no obligation. A salesperson comes to the house, goes through the attic and the roof, and gives you a price in writing that includes the decking.
You can see the full scope of the work on the roofing page or request a free estimate.
