T1-11 Siding Replacement and Repair in Salem, OR
Grooved plywood siding fails from its edges in. How to tell whether yours is also the wall's structural sheathing, and what that means for a Salem permit.
T1-11 is plywood siding with vertical grooves cut into its face, commonly sold in 4-by-8-foot sheets. It fails from the edges in: the cut bottom edge near the ground, the horizontal seams between sheets, and the corners of windows and doors. The detail that decides the job in Salem is what is behind it. When T1-11 serves as both the siding and the wall’s structural sheathing, replacing it needs a City of Salem building permit.
How do I know if my T1-11 is structural sheathing?
Look for a second layer. Some houses have T1-11 nailed over separate sheathing; others have T1-11 fastened straight to the studs, doing both jobs at once.
- In an unfinished garage or shed wall, look at the inside face of an exterior wall. If you can see the back of the grooved panels between the studs, with nothing else in between, the T1-11 is the sheathing.
- At a window, vent or damaged edge, see whether there is a layer of plain plywood or OSB behind the siding.
- Ask the contractor to confirm it before quoting. It changes the permit, the order of work and the price.
Does replacing T1-11 need a permit in Salem?
The City of Salem’s guidance on work exempt from permits says siding replacement and repair is exempt unless the wall must be fire-resistive, then adds a specific note: T1-11 needs a building permit when it acts as both the siding and the structural sheathing. Repairing or replacing any sheathing needs a permit too. West Salem follows the same city rules. In Keizer and the smaller towns, check with the local building office before replacing structural panels.
Repair a few sheets, or replace the siding?
Replace individual sheets when the damage is limited to one or two panels, the rest are sound, and the new sheets can be matched. Groove spacing varies between products, and weathered panels look different from new ones until painted. Each replacement needs its horizontal joints flashed and its bottom edge sealed.
Replace the siding when bottom edges are failing along whole walls, when the veneer is peeling on several sides of the house, or when the wall behind is wet. A siding replacement takes the panels off, deals with the framing or sheathing underneath, and rebuilds the barrier and flashing before new siding goes on. For panel-by-panel work, siding repair covers what a sound repair includes.
What can replace T1-11 siding?
- New T1-11 or other plywood panel siding, keeping the same look.
- Fiber cement vertical panels, such as James Hardie’s HardiePanel, for a panel look in a material that is not plywood, or fiber cement lap boards for a different look.
- Vinyl board-and-batten, a vertical style in vinyl siding.
- Lap siding over new sheathing, in fiber cement, engineered wood or vinyl.
Where the T1-11 was the structural sheathing, switching to lap siding or vinyl means replacing that bracing, such as with new sheathing, because lap siding and vinyl do not brace a wall. That is part of why these jobs are quoted after the contractor has confirmed what is there.
What Oregon’s code expects when T1-11 comes off
New siding goes over a water-resistive barrier (section R703.2 of the 2023 Oregon Residential Specialty Code), with kickout flashing where a lower roof edge meets a wall (R703.4) and, by default, a drainage space of at least 1/8 inch behind the siding (R703.1.1). A 2026 edition of the code is scheduled to take effect on October 1, 2026. Older T1-11 walls do not always have a barrier behind the panels, so expect one on the quote.
Is it rot, or is it a different siding problem?
Grooved panels are not always plywood. Hardboard panel siding can look similar, but it fails by swelling rather than peeling apart; see swelling hardboard or OSB siding. If the damage is in trim and sills around the panels rather than the panels themselves, start with dry rot in siding and trim.
Request a siding quote, mention that the siding is T1-11, and say whether you know if there is sheathing behind it. We connect you with an independent siding contractor who covers your ZIP code.
What you may notice
Outer layers of plywood peeling, bubbling or splitting away from the panel.
Bottom edges that are soft, swollen or crumbling along the base of the wall.
Dark staining or rot along horizontal seams between panels.
Rot at the corners of windows and doors.
Grooves and edges that stay dark long after the rain has stopped.
What causes it
T1-11 is grooved plywood, and it fails from the edges in: the cut bottom edge near the ground, horizontal seams with no Z-flashing, and the corners of windows. Where the panels are also the wall's structural sheathing, the City of Salem requires a building permit to replace them.
Bottom edges left unsealed, so they wick up water from splashback and wet ground.
Horizontal joints between panels installed without Z-flashing.
Panels ending too close to soil, decks or a roof surface.
Paint or stain worn through, exposing the face veneer to rain.
Window and door openings without head flashing.
How soon it needs attention
Plywood that has started to peel apart keeps taking on water through Salem's wet season, when November through January each average roughly six to seven inches of rain (NOAA 1991-2020 normals). Where T1-11 is the only layer between the weather and the framing, there may be nothing behind it to slow that water, so damage at the panel edges can move into the studs and sill plate. That is worth a contractor's look before another winter.
Request a Siding Quote
Describe the siding project once. Requesting a quote is free, with no obligation.
Services that fix it
Siding Replacement
A full tear-off and re-side: old cladding off, rotted sheathing repaired, then a new water-resistive barrier, flashing, trim and siding.
Siding Repair
Replacing damaged boards and trim, stopping leaks at flashing, and fixing rot before it reaches the wall behind the siding.
Fiber Cement Siding
Fiber cement lap, panel and shingle siding from makers such as James Hardie and Allura, in factory-primed or prefinished boards.
Common questions
Can damaged T1-11 just be painted over?
Paint protects panels that are still sound, but it will not reattach peeling veneer or shrink a swollen edge. Damaged sections need replacing, and the new panel edges should be sealed and flashed so they do not fail the same way.
Can I replace just one sheet of T1-11?
Often, if the damage is limited and the new panel's groove spacing and texture can be matched. Any horizontal joint needs flashing, and in Salem replacing a panel that also serves as structural sheathing needs a building permit.
How is T1-11 different from hardboard panel siding?
T1-11 is plywood, made of wood veneers glued in layers, and it tends to fail by the layers peeling apart. Hardboard panels are compressed wood fiber, and they tend to swell and go soft. Both can have grooves, so look at a damaged edge to tell them apart.
Does replacing T1-11 need a permit in Salem?
The City of Salem's permit guidance says T1-11 siding needs a building permit when it acts as both the siding and the structural sheathing. Where there is separate sheathing behind the panels, replacing the siding alone is exempt, unless the wall must be fire-resistive.
Request a Siding Quote
Describe the siding project once. Requesting a quote is free, with no obligation.