T1-11 Siding Replacement — Sheds, Garages and 1970s Houses
The grooved panels on the garage have gone soft along the bottom foot, the plies are separating at the seams, and paint will not hold anymore.
T1-11 siding replacement removes the grooved plywood or OSB panels that are rotting at the bottom edge and delaminating at the joints, braces or sheathes the wall if the T1-11 was doing that job, wraps it, and installs new panel siding or lap siding with Z-flashing at every horizontal joint. JMB Builders does it on sheds, detached garages and seventies houses across the Twin Cities metro. Licensed MN contractor BC809005, priced per project. Photo quote or free in-home estimate.
- T1-11 off, wall braced if the panel was the sheathing
- New LP panel or lap siding, Z-flashed at joints
- Bottom edge held off the grade and sealed
- Free in-home estimate
- Licensed MN contractor BC809005
Send photos and hear back within one business day — or book a free in-home estimate.
T1-11 is the grooved plywood or OSB panel siding on half the sheds, detached garages and split-levels built in the seventies and early eighties. It went up fast because one four-by-eight sheet was the sheathing and the siding at once. That is also why it fails the way it does: the bottom edge wicks water off the slab or the grade, the grooves hold water, the plies separate, and once the paint goes the panel is gone within a few seasons. On OSB T1-11 the bottom foot turns to mulch.
The structural part is the thing most people miss. On a lot of these buildings the T1-11 is the only thing bracing the wall; there is no sheathing behind it, just studs. Pull it off and the wall can rack. So the replacement is planned in order: panels come off one wall at a time, the wall is braced or sheathed with OSB before anything else, then wrapped, then sided. On a house, we sheathe. On a shed or a garage, a new panel siding rated to work as sheathing can do both jobs again, done right this time.
Done right means Z-flashing at every horizontal joint where a panel sits on top of another, a bottom edge held an inch or more above the slab or grade and sealed, the grooves and cut edges primed before paint, and a drip cap over every door and window. LP SmartSide panel siding is the usual replacement because it looks like T1-11 and comes primed or factory-finished. Lap siding is the other option and changes the look of the building entirely. Either way, the painting is its own line on the quote or you paint it yourself.
What you supply
- Photos of each wall, a close-up of the bottom edge and a photo of a seam where the plies are separating
- What the building is: shed, detached garage, attached garage or the house itself
- Panel or lap siding, and the color; factory-finished or primed for painting
- Access around the building and a spot for a small dumpster
What JMB supplies
- Removal and disposal of the T1-11 panels, trim and battens
- Wall bracing or new OSB sheathing where the T1-11 was the only sheathing
- Bottom plate and stud repair where the rot reached the framing, common on slabs
- House wrap with taped seams and flashing at every door and window
- New LP SmartSide panel siding or lap siding, with Z-flashing at horizontal joints and drip caps over openings
- Bottom edge held above the slab or grade, with the cut edges primed and sealed
- Corner boards and trim in matching material or PVC
- Painting or staining as its own line on the quote, or leave it primed and paint it yourself
How it is priced: per project
Quoted in writing from your photos, with a reply within one business day. What moves the number:
- Wall area and height; a shed is a day, a two-story house with T1-11 is a full siding job
- Whether the wall needs sheathing or bracing once the T1-11 comes off
- Bottom plate and stud repair, worst on garages and sheds on a slab
- Panel siding vs. lap siding, and primed vs. factory-finished
- Number of doors, windows and the overhead door to trim and flash
- Painting as a separate line
- Access and whether the building is attached to the house
A photo of the bottom edge where it meets the slab tells us how much framing is involved. Tell us if the inside of the wall is open so we can see if there is sheathing behind the panel.
How long it takes
A garden shed: one day. A detached garage: two to three days. A seventies house with T1-11 on every wall: about a week. Painting is scheduled after the primer has cured.
How your project works
- 1
Send photos, get a written quote
Send three photos of the space and a sentence about what you want. You get a clear, itemized reply within one business day. Prefer a look in person? A free in-home estimate is always an option.
- 2
Pick materials, or bring your own
We help you choose profiles and materials that fit the house and the budget, or match your existing millwork exactly — or you buy the door or trim yourself and we install it. Everything is confirmed before the crew is scheduled.
- 3
Clean, precise installation
The crew shows up on time, protects floors and furniture, and installs with tight joints and consistent reveals. Photos of the finished work go in your job folder.
- 4
Walkthrough and invoice
We walk the finished work with you. If anything is not right, we fix it before we call the job done. Then one invoice, paid by check or direct deposit — no card fees, no payment links.
Situations and options
T1-11 to LP SmartSide panel
Grooved engineered wood panels that look like the T1-11 did, primed or factory-finished, with treated edges. Z-flashed at joints and held off the slab. The usual choice when you want the building to look the same, only sound.
T1-11 to lap siding
Sheathe the wall, wrap it, and run lap siding in LP SmartSide or vinyl. Changes the look from a seventies panel building to a sided one, and matches the house if the house has lap.
Shed or garage on a slab
The bottom plate and the first foot of stud are often rotted with the panel. We cut out and replace the framing, set a treated plate, and keep the new siding an inch or more off the concrete so it does not happen again.
Bottom two feet only
When the panels are sound above the rot line, we cut the wall at a clean line, replace the bottom section with new panel and a Z-flashing at the joint, and prime it to paint. A budget fix that buys years.
T1-11 Siding Replacement — Sheds, Garages and 1970s Houses: questions, answered
What is the best replacement for T1-11 siding?
LP SmartSide panel siding if you want the same grooved look: it is engineered wood with treated edges, comes primed or finished, and resists rot and woodpeckers better than plywood T1-11 did. Lap siding over new sheathing if you want to change the look. Either way the details that killed the T1-11 get fixed: Z-flashing at joints, a bottom edge held off the grade and sealed, and drip caps over the openings.
Why is my T1-11 rotting along the bottom?
The bottom edge was set on or near the slab or the dirt and it wicks water up into the plies, and the grooves channel rain straight down to it. Once the paint fails on the edge the panel drinks every rain and every snowbank. OSB T1-11 goes faster than plywood. The fix on the new siding is a bottom edge an inch or more above grade, primed on the cut, with a drip or a flashing above the foundation.
Is T1-11 structural, and what happens when it comes off?
On many sheds, garages and some seventies houses the T1-11 is the only sheathing and the only wall bracing. Take a whole wall off and it can rack. We strip one wall at a time, brace or sheathe it before anything else, then wrap and side. On a house we sheathe with OSB. On a shed or garage, a panel siding rated to work as sheathing can do both jobs again.
Can you replace only the bottom two feet of T1-11?
Yes, when the panel above is sound. We cut a straight line across the wall above the rot, remove the bottom section, repair the plate and studs if needed, set a new panel section with a Z-flashing at the joint, and prime it to paint. It is a budget repair that buys years. If the plies are separating higher up as well, the whole panel is the better answer.
Does the new panel siding have to be painted?
Primed panel siding needs paint; factory-finished panel comes in a color and does not. If you choose primed, painting is quoted as a separate line on the job, or you can leave it primed and caulked and paint it yourself. Either way the cut edges and grooves get primed before the panels go up, which is where plywood T1-11 was never protected.
How long does it take to replace T1-11 on a garage?
Two to three days for a detached two-car garage with one crew: strip and brace one wall at a time, repair the plate where it is rotted, wrap, side and trim the overhead door and service door. A shed is a day. A house with T1-11 on every wall is a full siding job, about a week. Painting follows after the primer cures.
Recent JMB work, from our job log
59 installs recorded across 30 Twin Cities communities since Dec 2025. Window and door installs for homeowners, builders and dealers. Counts come straight from our job log; no customer names.
Get a written quote for this job
Three photos and a sentence is enough: a reply within one business day, or ask for a free in-home estimate. Or text the photos to 763-333-4066.
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Read morePage reviewed October 2, 2026 · JMB Builders LLC, MN license BC809005 · All siding pages
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