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When Does Roof Decking Need to Be Replaced?
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When it will no longer hold a fastener, and Oklahoma is unusually specific about what that means. The state amendment to the roofing chapter defines a solidly sheathed deck as sawn lumber boards or structural panels that provide solid holding power for fasteners, and it expressly excludes decking with gaps wider than the roof covering manufacturer allows, and boards that are warped, split, cracked, deteriorated or rotten. That turns “the deck looks fine” into something checkable. Arrowhead Roofing has torn off northeast Oklahoma roofs since 1987, and decking is the most common thing found once the old roof is off and the least predictable thing on any estimate.
Note: this is a general guide. Code editions and local amendments change, and the condition of a particular deck is a judgement made on the roof with the covering removed rather than from a photograph or from the ground.
Five conditions send decking to the skip, and only the first is the one people expect.
| Condition | What it looks like | Replace? |
|---|---|---|
| Rot or water damage | Dark, soft, delaminating plies, often near a valley, wall or penetration | Yes |
| Warped, split or cracked boards | Cupping, splits along the grain, cracks through the board | Yes, named in the definition |
| Gaps too wide | Spaced sheathing, or boards that have shrunk apart | Yes, where wider than the manufacturer allows |
| Too thin for the rafter spacing | Not visible. Measured | Upgraded rather than replaced, commonly by adding a layer |
| Previous fastener damage | A field of old nail holes where a layover was removed | Sometimes. It is a holding-power judgement |
The Short Answer
The deck is the part of the roof that everything else is attached to. Its job is to hold nails. When it stops doing that reliably, nothing installed on top of it performs as designed, however good the shingle is.
That is why the Oklahoma definition is written around holding power rather than around appearance. A board can look acceptable and still be unable to grip a fastener, and a board with some staining can be perfectly sound.
The Thing Nobody Can Price in Advance
Worth being straight about, because it is the single most common source of a change order on a roof.
Decking is under the roof. Until the covering is off, nobody knows exactly how much of it is bad. An experienced estimator can predict it: the age of the house, the presence of a previous layover, a known leak, a valley that has been patched. Prediction is not measurement.
So a properly written estimate carries decking as a rate rather than as a fixed quantity, and an estimate that promises no decking will be needed is either lucky or not being straight with you. How much does a new roof cost in the Tulsa area? covers where that sits among the other inputs.
The Rafter Spacing Problem, Which Is Not About Rot
A different question entirely and one homeowners are rarely told about.
Decking has to span between rafters without deflecting, so the required thickness depends on how far apart the rafters are. Where rafter spacing runs over 24 inches, the decking has to be upgraded to a minimum of 5/8 inch, and on a re-roof that is commonly done by adding a layer over the existing rather than stripping it.
On the ridealong that produced a lot of the material on this site we measured rafters at 24.25 inches with calipers. A quarter of an inch decided whether that roof needed a decking upgrade, which is exactly the kind of thing that is invisible from the driveway and expensive to discover late.
The Older Tulsa Problem: Spaced Sheathing
A good part of the older housing stock here was originally roofed in wood shake, and shake was laid over spaced sheathing, boards with deliberate gaps between them so the shakes could breathe.
Asphalt shingles cannot be fastened to that. The code requires a solidly sheathed deck, so a shake-to-asphalt conversion means sheeting the entire roof before a single shingle is ordered. Some of those roofs were converted decades ago and some were not, and you generally find out at tear-off.
This is a whole-roof cost rather than a patch, and it is the biggest single surprise available on an old Tulsa house.
What You Can Check Yourself, From Inside
Two things, and neither requires going on the roof.
Go into the attic with a torch on a bright day. Daylight through the deck is obvious, but the more useful signal is staining: dark patches on the underside of the sheathing, or on the rafters, mark where water has been even if it is not coming through now.
Look at the roof line from across the street. A deck that has begun to fail often shows as a gentle dip or wave between rafters. A brand new roof over a tired deck shows it more clearly, not less, because the new surface is flat enough to reveal what is under it.
What Changes the Answer
Three things move a deck from sound to a line item.
Whether there has been a layover
Two layers of shingles mean twice the fastener holes and twice the weight, and removing them exposes a deck that has been worked harder. Oklahoma does not permit shingles over shingles, and can you put a new roof over an old one? covers why.
Where the water has been going
Deck damage is not random. It concentrates at valleys, at wall junctions, around chimneys and under any detail that has been failing. That is why the flashing conversation and the decking conversation are the same conversation: what is step flashing and counter flashing?
How long the roof went past its life
A roof replaced on time usually has a sound deck. A roof replaced three years late frequently does not, and the deck cost is the part of that delay that people do not budget for.
Related Questions
How long should the roof have lasted anyway?
Less than the marketing suggests in a hail market. How long does a roof last? covers service life against the local storm record.
Does this change how long the job takes?
It is the single most common reason a one day job becomes two. How long does a roof replacement take? covers the day and what stretches it.
Will insurance pay for decking?
Where it is a code requirement the regulator has taken a position on that. Does insurance have to pay for building code upgrades on a roof in Oklahoma? quotes it.
See Also
The two answers next to this one are why the old roof has to come off first, and how decking sits among the other cost inputs.
Find Out What Is Under Your Shingles Before You Budget
We have torn off northeast Oklahoma roofs since 1987, and we will tell you what we expect to find and why, before anybody signs anything. Book a free roof inspection and we will start in the attic.