Corte Madera T1-11 Siding

If you own a mid-century or ranch-style home in Corte Madera, there's a good chance you're looking at T1-11 — the grooved plywood or OSB panel siding that went up on so many houses built from the 1950s through the 1970s, and on plenty of sheds and additions since. It gave those homes their clean vertical lines cheaply. The problem is that T1-11 lives or dies by its coating: once the paint or sealer fails and water gets into the panel, it swells, delaminates, and rots. Bay Area Siding Company works on T1-11 across town — most often replacing panels that have reached the end of the road, and sometimes reinstalling it where a homeowner wants to keep the rustic, period look. As a Larkspur-based crew a few minutes away, we can come take a real look at what you've got.

Find out where yours stands. Call (415) 619-5167 or request a bid.

How to tell your T1-11 is done

T1-11 sends clear signals when it's failing. Walk the walls and look for:

• Swelling or splitting at the bottom edges of panels, where water wicks up
• Delamination — the plywood plies separating, or the OSB surface crumbling and flaking
• Dark staining, soft spots, or a spongy feel when you press on the panel
• Paint that won't hold no matter how many times it's redone
• Gaps opening at the grooves, seams, or Z-flashing where the barrier has broken down

A panel or two can sometimes be swapped. When the failure is widespread — which is common on homes that are fifty or sixty years into their life — it's usually time to talk about re-siding the walls rather than chasing individual panels.

The most common decision: what replaces it

When T1-11 comes off in Corte Madera, most homeowners don't put T1-11 back. They use the opportunity to move up to a cladding that won't hinge on a paint film to survive:

• Fiber cement — noncombustible, rot- and pest-resistant, and the sensible choice for homes on the wooded hillsides where fire is a factor (more on that below).
• LP SmartSide engineered wood — if you want to keep a genuine wood look and, in vertical panel or board profiles, something close to the original T1-11 character, with far better rot resistance.

Both are a real step up from a plywood panel that depends on being repainted on schedule to stay intact.

When keeping the T1-11 look makes sense

Not everyone wants to change the look. On some period homes — and where the budget or the aesthetic calls for it — reinstalling fresh T1-11 or a comparable grooved panel is a legitimate choice, as long as it's detailed correctly: properly primed and painted on all edges, with the Z-flashing at horizontal joints and the grooves and seams sealed so water can't get behind it. Done right and maintained on a coating cycle, it can serve well. We'll tell you honestly whether that's the smart move for your house or whether an upgrade pays off better over time.

The fire question on the hillside

If your T1-11 home is on Christmas Tree Hill or up the wooded parts of Chapman Park, the material conversation changes. Plywood and OSB panel siding is combustible, and that terrain — reflected in CAL FIRE's 2025 Fire Hazard Severity Zone and WUI maps and served by Central Marin Fire Department — is where fire resistance carries weight. Where a parcel sits in a designated hazard zone or the WUI, California Building Code Chapter 7A governs the wall covering and generally favors noncombustible or ignition-resistant assemblies, which points a hillside T1-11 replacement toward fiber cement rather than another wood-based panel. Whether 7A applies to your parcel and scope is something we confirm with the Town of Corte Madera and the fire authority before we spec.

What replacement involves

Because T1-11 panels are often the structural sheathing and the finished siding at once, a replacement gets particular attention at tear-off. We assess the walls, measure, and pull the Town of Corte Madera building permit — the town is on the 2025 California codes as of January 1, 2026. We remove the old panels and inspect what's behind and around them: the framing where panels served as sheathing, and the water-resistive barrier and flashing. Concealed rot gets repaired. We establish a proper WRB and flashing, then install your chosen cladding to spec, and finish with trim, paint where applicable, cleanup, and a walkthrough.

Cost drivers

We quote after we've seen the walls. What moves the number: how much of the panel and any underlying framing has rotted; whether you're upgrading to fiber cement or engineered wood or reinstalling panel siding; the home's size and number of stories; hillside access; and trim and window integration.

Weighing your options? Compare fiber cement, LP SmartSide, and natural wood, or start at the siding replacement hub. We also do window replacement in Corte Madera, serve the Marin service area, and show completed work in the projects gallery.

Frequently asked questions

Can my T1-11 be repaired instead of replaced? Sometimes — a localized failure can be patched or a panel swapped. But when swelling, delamination, and rot are widespread, which is common on older Corte Madera homes, replacing the wall usually makes more sense than chasing panels.

What should I replace T1-11 with? Most homeowners move to fiber cement or LP SmartSide. Fiber cement is noncombustible and lowest-maintenance; SmartSide keeps a warm wood look, including panel profiles close to the original. On a fire-exposed hillside parcel, fiber cement is the better fit.

Is T1-11 okay on a home in the fire zone? It's combustible, so on a designated hazard-zone or WUI parcel we'd generally recommend replacing it with a noncombustible material rather than another wood panel. We confirm your parcel's designation with the Town and Central Marin Fire.

Do I need a permit to replace T1-11 in Corte Madera? Yes. It's permitted work through the Town of Corte Madera Building Division, and because panels can double as sheathing, the tear-off inspection matters. We handle the permit.

Get your T1-11 assessed

Call (415) 619-5167 or request a bid. We'll tell you honestly whether to renew the panels or upgrade the wall, and lay out the scope either way.