What Is T1-11 Siding? Problems, Repair and Replacement

What T1-11 is made of

T1-11 (often written T-111 or T1-11) is a type of panel siding with vertical grooves cut into its face, usually spaced 4 or 8 inches apart, so it looks like vertical boards. Most T1-11 is plywood with a rough-sawn or textured face, sold in sheets about 4 feet wide and 8, 9 or 10 feet tall. Some panels are made of OSB with a textured overlay. The edges are shiplapped so neighboring panels overlap.

Builders like it because a single panel serves as both sheathing and siding, it goes up quickly and it is cheap. That is why it is everywhere on ranch homes, split-levels, cabins, sheds, detached garages and the gable ends of houses built from the 1970s onward.

How to recognize it

• Large vertical panels with evenly spaced grooves.
• Horizontal seams every 8 to 10 feet on tall walls, often covered with a metal Z-flashing.
• Rough, wood-grain texture, usually painted or stained.
• Edges that show plywood layers where the paint has worn.

Why T1-11 fails

• Bottom edges. The bottom edge of each panel is end grain plywood, which wicks water. When it sits too close to soil, concrete or a roof, or when splashback hits it, the edge swells and the layers separate.
• Horizontal joints. Where one panel sits above another, missing or failed Z-flashing lets water into the joint.
• Paint failure. T1-11 depends on paint or stain to shed water. When the finish wears through, especially on sunny Kansas walls, the face checks and weathers.
• No separate sheathing. Because the panels are often the only layer, there may be no water-resistive barrier behind them, so water that gets through goes straight to the framing.

Repair or replace?

Individual T1-11 panels can be replaced, and damaged bottom edges can sometimes be cut off and flashed with a trim board. Repair makes sense when damage is limited to a few panels and the rest are sound. Replacement makes sense when:

• Bottom edges are swollen or delaminated on many panels.
• The face is checking and weathering faster than you can paint it.
• Framing or sill plates behind the panels are damaged.
• You want a different look or better performance.

Because T1-11 often acts as sheathing, replacing it can mean replacing the structural layer of the wall. A contractor should check whether new sheathing is needed and how the wall will be braced.

Replacement options

• Engineered wood panels such as LP SmartSide come in grooved panel profiles that look similar to T1-11, and are a common replacement on sheds, garages and outbuildings.
• Board and batten in fiber cement, engineered wood or vinyl gives a vertical look with better water shedding.
• Lap siding in vinyl, fiber cement or engineered wood over new sheathing and house wrap, for a completely different look.
• Steel panels for outbuildings. See steel siding.

Doing it right the second time

• Add a water-resistive barrier behind the new siding, even on outbuildings if they are heated or finished inside.
• Keep the required clearance between the bottom of the siding and the ground, concrete and roofs.
• Flash horizontal joints and the tops of windows and doors.
• Seal cut edges and paint promptly.
• Manage water: gutters, downspout extensions and grading away from the wall.

Older homes and lead paint

T1-11 on houses built before 1978 may have lead paint layers. Contractors disturbing more than small painted areas on those homes must follow the EPA's lead-safe rules. Avoid sanding or power washing old painted panels yourself.

Maintaining T1-11 you want to keep

• Keep the finish up; repaint or restain before the face weathers.
• Seal the bottom edges and keep them clear of soil, mulch and splashback.
• Check Z-flashing at horizontal joints.
• Caulk around windows and trim.

T1-11 on sheds, barns and garages

Around Wichita, T1-11 is most common on outbuildings: backyard sheds, detached garages, shops on acreages and pole buildings with wood-sided walls. These buildings often have no gutters, sit close to the ground and get less paint attention than the house, so their panels fail first. For unheated buildings, steel panels or engineered wood panel siding are common replacements. If you are re-siding the house, ask whether matching the outbuildings at the same time makes sense; one setup and one material order can be more efficient than separate projects.

Getting a quote

When you request a quote, mention that the house or building has T1-11 and describe where it is failing. We will call you back to set up a free quote. Published ranges are in the siding cost guide.

Related services

• LP SmartSide Engineered Wood Siding: Engineered wood siding with a real wood look, lighter than fiber cement and popular on garages and shops.
• Old Asbestos & Aluminum Siding Replacement: Replace aging asbestos-cement, aluminum, hardboard and T1-11 siding with the right precautions.
• Siding Repair: Fix cracked, loose, blown-off or rotted sections before water gets behind the wall.

Sources: HomeGuide, house siding cost; EPA, Renovation, Repair and Painting (lead-safe) program.

Good to know: Requesting a quote is free and there is no obligation. Ask for a written quote that lists the material, the scope, permits and the warranty terms.