When the Decking Has to Come Off Too

November 2026

The layer under the layer

Most people pricing a new roof picture shingles coming off and shingles going back on. That is how most jobs go. Every so often, though, the crew strips a slope down and finds that the wood underneath cannot take another roof, and the job grows a step: some or all of the decking has to come off too.

Nobody likes a surprise on replacement day, and most deck surprises can at least be suspected ahead of time. Our roof deck replacement work around Herriman often starts on newer sheathing, because so much of Herriman is newer construction.

What decking is, and the kinds we find

The deck is the wood surface the whole roof is fastened to, laid across the rafters or trusses. Every nail in every shingle is only as good as the wood it is driven into.

On newer houses the deck is almost always OSB or plywood in full sheets; older homes with plank or spaced boards are a different job, and we cover those elsewhere on the blog.

Where newer sheathing goes wrong

OSB is the deck on most newer roofs, and its weak point is the edge. The faces of a sheet are sealed at the mill, but the cut edges drink water, and once they do they swell. A swollen edge stands proud of the sheet beside it, and that raised seam shows through the shingles as a faint ridge running across the slope. On a tear-off, swollen seams are often the first thing we notice, and the wood along them is usually softer than the middle of the panel.

Panels are also meant to go down with a small gap between them. Wood moves with heat and moisture, and sheets butted tight with no room to grow push against each other until the seams buckle upward. Where the long edges between rafters need support, metal clips are supposed to hold neighboring panels level. When the gaps or the clips were skipped, the deck sags between supports and the joints lift, and a shingle roof laid over it never sits flat.

The other weak spots are the details at the edges of the roof. At the eave, a deck that never got ice-and-water shield carried past the interior wall line takes on meltwater every winter, and the bottom row of sheets pays for it. In a valley, membrane that was skipped, torn or lapped the wrong way sends water straight onto the seam where two slopes meet. Both look the same once the roof is open: a band of dark, soft wood right where the detail failed, and sound sheathing a few feet past it.

Signs before anybody climbs up

Some deck problems announce themselves from the ground or the attic if you know where to look.

From outside, look along the roofline at low sun. A dip between rafters, a slope that sags in the middle, or a ridge line that is no longer straight usually means the wood underneath has softened or the framing has moved. Shingles that look rippled in one area and flat everywhere else point the same way.

From the attic, bring a flashlight. Dark staining on the underside of the sheathing, especially around vents, chimneys and along valleys, marks where water has been getting in. Rust at the nail points coming through the deck is another tell, since the moisture that rusts a nail is also soaking the wood around it. Daylight showing through the boards is the clearest sign of all. Press a knuckle into a stained spot; if the surface gives, the sheet is done.

What the tear-off shows

The truth comes out when the shingles and underlayment are off and the bare wood is in daylight. We walk every slope at that point, before anything new goes down.

Rotted sheathing goes dark first, then soft, then starts to come apart in layers around the fasteners. OSB that has been wet for years swells and crumbles at the edges. Plywood delaminates, its plies separating so the sheet feels spongy underfoot. A sheet can look fine on top and still be soft enough that a nail driven into it will never hold.

The pattern usually tells a story. Rot clustered around a pipe or flue means a failed flashing. Rot along the bottom few feet of the roof means water getting past the eave, often from ice. Rot in a stripe down a valley means the valley was never sealed properly. Finding the cause matters, because laying new wood under the same failed detail just starts the clock again.

A few sheets or the whole roof

Most re-decks are partial. A section around a chimney, a run along an eave, a valley and the sheets on either side of it. We cut out the bad wood back to sound material, making sure the edges of the new sheets land on framing, and lay fresh sheathing of matching thickness so the new section sits flush with the old.

A full re-deck happens when the bad spots are spread across most of the roof, when swollen seams and sagging panels run across every slope, or when the existing deck is too thin or too uneven to hold a new roof flat. In those cases fresh sheets go across every slope.

Whichever it is, you see it before we do it. We photograph what we find, show you the soft areas, and talk it through while the crew is standing on the roof.

Why the slow leak does the most damage

The leak that stains a ceiling in a week is the lucky one. Somebody sees it, calls, and the hole gets closed while the wood around it is still sound. The leak that ruins a deck is quieter. It lets a cup of water into one rafter bay every storm, year after year, and nothing ever shows inside, because the insulation soaks it up and the attic dries out again between storms.

Meanwhile the sheathing in that bay goes dark, then soft, then starts to separate around the nails. By the time anyone notices, it is usually because a shingle lifted where its nails lost their grip, or because somebody went into the attic for a holiday box and saw daylight. That is why we look hard at every vent, valley and wall joint on a tear-off, even on a house that never had a ceiling stain.

Shingles are a material cost. The structure under them is what the whole house leans on, and keeping it sound is the reason we would rather replace a few sheets now than leave soft wood under a new roof. You can see what stripped decks and new sheathing look like on finished jobs in our gallery.

How it changes the day

Most houses in this valley are a one to two day replacement once the crew is on site. Deck work adds to that, how much depending on how many sheets come out. A few sheets fit into the normal day. A full re-deck is its own step between tear-off and underlayment.

The house is never left open. Bare decking that is not covered by evening gets underlayment over it before the crew leaves, so a passing storm does not soak the new wood. Covering what sits directly below the work inside is worth a few minutes, because old nails and attic dust shake loose when boards come out.

The new deck is fastened with galvanized nails into the framing, then the roof goes on exactly as it would over any sound deck, carrying our 10-year workmanship warranty. More on the service itself is on the roof deck replacement page, and the Herriman page lists what else we do in town. Call (801) 382-8898 or use the contact page if your attic is showing any of the signs above.

Questions about decking

Can you tell before the tear-off whether the deck needs work?

Often, yes, at least in part. An attic look and a walk on the roof show soft spots, staining and sag. What we cannot see is wood hidden under sound shingles, so we always say plainly that the final answer comes once the old roof is off.

Will new decking make my roof look different?

It should make it look flatter. Old decks with soft or swollen sheets push waves into the shingles above them. Fresh sheathing at the right thickness gives the new roof a straight, even surface, which is easiest to notice along the ridge and the eaves.

Why not just shingle over the soft spots?

Nails driven into rotted wood do not hold, so the shingles above a soft spot can lift in the first strong wind. The rot also keeps spreading if the cause is still there. Covering it only hides a problem that the next roofer will have to tear back into.

Does my newer house really need deck work?

Usually not. Newer homes mostly need only a sheet or two, if anything, around a flashing or vent that let water in over the years. A full re-deck is rare on newer construction and more common on older homes with plank boards or spaced sheathing.

What happens to the old wood?

Rotted sheets come out and go into the dump trailer with the tear-off. Sound plank or spaced boards on older homes often stay in place under the new sheathing. Either way we clean up what comes off, including the nails that shake loose along the way.

Solid wood first

A roof can only be as sound as the deck it is nailed to. Finding the soft spots early, and fixing what caused them, is what lets the new shingles last. Reach the family at (801) 382-8898 or through the contact page.