San Rafael T1-11 Siding

T1-11 is the vertical, grooved plywood panel siding found on many San Rafael houses, garages, additions, and outbuildings. Much of it has been in place for decades, and a lot of it is now swelling at the bottom edge, peeling paint faster than anyone can repaint, or going soft near the ground. Bay Area Siding Company works on T1-11 homes across San Rafael, from mid-century streets in Terra Linda to older lots around Gerstle Park and the hillsides above downtown. We're based in Larkspur, a short drive down the 101.

We handle three kinds of T1-11 jobs. We replace damaged panels with new grooved panel siding, re-side the whole house in new T1-11 where you want to keep the look, or replace failing T1-11 with a more durable material such as fiber cement or engineered wood.

Want someone to look at your panels? Call (415) 619-5167 or request a bid.

First question: is your T1-11 also your sheathing?

This matters more than anything else on a T1-11 job, and many homeowners don't know the answer until we look.

On a conventional re-side, removing the old cladding exposes the sheathing, the water-resistive barrier (WRB), and the flashing. We can then inspect and repair those layers and install new siding over a sound substrate. The framing stays covered.

T1-11 often works differently. On many older homes the panels were nailed directly to the studs and serve as both the siding and the sheathing. There may be little or no separate WRB behind them. In that case, removing the T1-11 does expose the framing. The new wall then needs new structural sheathing, a new WRB, and new flashing before any cladding goes on.

That changes the scope and the cost. Panel siding can also contribute to a wall's bracing, so on homes where the T1-11 is doing structural work, the replacement has to keep that function. We confirm the requirements with the City of San Rafael's Building Division as part of the permit. At the consultation, we check how your walls were built, usually at an outlet, an attic edge, or an already-damaged panel, before we quote anything. That way the estimate reflects your actual wall.

How T1-11 fails, and why it happens where it does

T1-11 is plywood, or sometimes OSB, with its face and grooves exposed to the weather. It holds up as long as the paint or sealer does. Once water gets past the finish, the panel starts to break down. The typical warning signs on San Rafael homes are:

• Swollen, flaring bottom edges where panels sit close to grade, soil, or mulch.
• Delamination. The face veneer lifts or bubbles, and the plies separate at the edges.
• Failed horizontal seams. Where one panel stacks on another, a missing or rusted Z-flashing lets water run behind the lower panel.
• Soft spots you can press in, especially under windows and at inside corners.
• Paint that won't stay on. It peels within a season or two, often because the wood underneath is wet.
• Grooves that trap dirt and moisture on shaded, north-facing, or fog-damp walls.

San Rafael's mix of foggy mornings, shaded wooded lots, and warmer inland afternoons isn't unusual for Marin. What matters is the exposure of each wall. The shaded side of a Sun Valley house, or a wall behind dense landscaping, stays damp longer than a sunny south face. That wall is usually where the rot starts, so our inspection focuses there.

Repair, re-install, or replace?

Spot repair makes sense when damage is limited to a few panels and the rest of the siding is sound. We cut out the failed sections, check what's behind them, correct the flashing, and install new panels. Matching is the challenge. Groove spacing, panel thickness, and texture vary between products and eras, and an exact match to 1970s panels isn't always available. Painting the whole elevation usually hides the difference.

Re-siding in new T1-11 keeps the rustic, vertical look that suits many mid-century and cabin-style homes. Installed correctly, with a proper WRB, flashed seams, clearance above grade, and a finish that's maintained, new panels perform far better than the originals ever did. It's often the most budget-friendly way to re-side. The trade-off doesn't change: T1-11 is still wood-based and will need regular repainting or sealing.

Replacing T1-11 with another material is the most common choice we see when a whole house has failed. The main options are:

• Fiber cement in vertical panel or board-and-batten profiles. It's noncombustible and resists rot and pests. It's also heavier and needs careful installation. Our San Rafael James Hardie page covers the Hardie line specifically.
• LP SmartSide engineered wood. It offers panel profiles with a real wood texture, it's lighter and easier to work than fiber cement, and it needs periodic paint.
• Natural wood such as board-and-batten or shiplap. It gives a premium natural look but requires the most maintenance.

For a broader comparison, including vinyl, see our San Rafael siding replacement page.

Mid-century homes: keeping the vertical lines

Vertical panel and board siding is part of the mid-century look found in parts of San Rafael, including Terra Linda's Eichler-era neighborhoods. If you like how your house looks and just want walls that stop rotting, you don't have to give up that look. Grooved fiber cement and engineered-wood panels can reproduce the vertical rhythm. New T1-11 is also an option if you want real plywood texture. We'll talk through groove spacing, trim details, and paint colors so the house still looks like itself when we're done.

Fire-zone parcels: a real factor for plywood

T1-11 is combustible. That's a real consideration in San Rafael, because parts of the city sit in mapped Fire Hazard Severity Zones and Wildland-Urban Interface areas. The state's 2025 Fire Hazard Severity Zone update extended mapping across Local Responsibility Areas. The City has noted that the new maps largely mirror its existing WUI boundaries, which already carry specific building requirements.

Chapter 7A of the California Building Code sets standards for particular exterior assemblies, including exterior walls. Whether and how those standards apply to your re-side depends on your parcel's designation, the product, and the scope of work. So we don't treat it as a blanket rule. We check your address and confirm the requirements with the City before specifying material.

On a WUI parcel, choosing a noncombustible option like fiber cement is often simpler than trying to qualify a wood-panel assembly. San Rafael also enforces vegetation-management standards citywide, and those apply regardless of what siding you choose.

Permits and what the job looks like

Re-siding a San Rafael home generally requires a building permit from the City's Building Division, and we handle that process. A typical job runs like this:

1. We inspect the walls and determine whether the T1-11 is also the sheathing.
2. We agree on the material and the scope.
3. We pull the permit.
4. We remove the old siding and repair whatever it exposes. That may be sheathing, WRB, and flashing, or new sheathing over the framing if the panels were structural.
5. We install the new cladding with flashed seams and openings, then finish the trim and paint.

If you're also replacing old windows, doing it while the walls are open lets us flash the new windows properly. See San Rafael window replacement.

What drives the cost

We price after we see the house, but these factors move the number:

• Whether new sheathing is needed behind the T1-11.
• How much hidden rot turns up.
• The material you choose (new T1-11, engineered wood, or fiber cement).
• Wall area and height, and site access on hillside lots.
• Trim and window flashing details.
• Any requirements tied to your parcel's fire-hazard designation.

A small repair and a full structural re-side are very different projects, and we'll be clear about which one you have. You can see completed exteriors in our project gallery.

Frequently asked questions

Can I just paint over my swollen T1-11? Paint can protect sound panels, but it won't fix delaminated or water-damaged plywood. It also won't fix a missing Z-flashing or a missing WRB. If the edges are flaring or the panels are soft, the damaged sections need to be replaced.

Will removing my T1-11 expose the studs? Only if the panels were installed directly on the framing as combined siding and sheathing, which is common on older homes. Where there's separate sheathing behind the T1-11, removal exposes the sheathing and WRB, and the framing stays covered. We determine which you have before quoting.

My San Rafael home is in a fire hazard zone. Can I still use T1-11? It depends on your parcel's designation and the specific product and assembly, so we confirm with the City before recommending anything. On many WUI parcels, a noncombustible option such as fiber cement is the more straightforward choice.

Can you match my Terra Linda home's vertical siding? Yes. We can install new grooved T1-11, or grooved fiber cement or engineered-wood panels that keep the vertical, mid-century look with lower upkeep.

Talk to a Marin crew about your T1-11

Whether you need a few panels replaced or the whole house re-sided, we'll tell you what's behind your siding and what it will take to fix it properly. Call Bay Area Siding Company at (415) 619-5167 or request a bid. We serve San Rafael and the rest of the Marin County service area from Larkspur.