If your Alamo home was built or remodeled in the mid-century decades, there is a fair chance it wears T1-11 — the grooved plywood or OSB panel siding that gave so many ranch homes, older tracts, sheds, and detached studios their vertical-line look. It is an inexpensive, honest material with one demand: it has to stay sealed. Where it does, it lasts; where the paint film breaks and water gets into the edges or the grooves, it swells, delaminates, and rots. Most of the T1-11 calls we get in the San Ramon Valley are about exactly that failure. Bay Area Siding Company, a Larkspur-based siding and window contractor, handles T1-11 repair, full replacement, and upgrades to more durable materials.

Not sure how far gone it is? Request a bid or call (415) 619-5167 and we will look at it.

Is your T1-11 failing, or just tired?

Panel siding gives clear warning signs. Walk the elevations and look for:

• Swelling or spongy spots at the bottom edges of panels, where water wicks up into the plies.
• Delamination — the face veneer lifting, bubbling, or peeling away from the panel.
• Dark staining, soft grooves, or visible rot near trim, windows, and where two panels meet.
• Failed or chalking paint that no longer sheds water — the root cause of nearly every T1-11 problem.
• Gaps at the panel joints or Z-flashing that let water behind the siding.

If the damage is isolated — a panel or two at a splash zone — a targeted repair and repaint may buy real years. If the face is delaminating across multiple elevations, or water has been getting in long enough to reach the substrate behind, replacement is the honest answer. We will tell you which situation you are in rather than defaulting to the bigger job.

The three paths from here

Homeowners with aging T1-11 in Alamo usually choose among three routes:

1. Repair and repaint. Replace the failed panels, re-flash the joints, and get a sound paint film back on. Lowest cost; right when the failure is localized and the substrate behind is dry.
2. Replace with a more durable material. By far the most common upgrade. We tear off the old panels and re-side in fiber cement or LP SmartSide engineered wood — both far more forgiving of missed maintenance than plywood siding, and fiber cement noncombustible for parcels near the wildland edge.
3. Re-install T1-11. Some owners genuinely want the original rustic, vertical-groove look — on a period ranch, a barn-style outbuilding, or a studio — and we can re-side in fresh T1-11, properly primed on all edges and flashed, so it starts its service life sealed.

Why replacement so often wins here

T1-11's low upfront cost is real, but its lifetime cost depends entirely on upkeep, and Alamo's climate is not gentle on a paint film — hot, dry, sun-heavy summers bake the south and west faces, and any lapse in repainting is where the water eventually gets in. Owners re-siding a main residence frequently decide that moving to fiber cement or engineered wood ends the swelling-and-repainting cycle for good. On sheds and secondary structures, re-installing T1-11 or a simple repair often makes more sense. Matching the fix to the building is the whole game.

What replacement involves

When we replace panel siding, tear-off removes the T1-11 down to the sheathing and substrate — worth emphasizing with this material, because a common surprise is that long-standing water intrusion behind failed panels has reached the water-resistive barrier and flashing or the substrate beneath. We inspect and renew the WRB and flashing before new cladding goes up. If the sheathing itself has rotted, that is a larger scope we would flag on discovery rather than paper over.

Because Alamo is unincorporated, the work is permitted and inspected through Contra Costa County's Department of Conservation and Development, Building Inspection Division in Martinez. We handle the County application and inspections. For parcels near the Las Trampas or Diablo wildland grade, a switch to noncombustible fiber cement can also address fire-area material questions — whether those rules apply depends on the parcel's designation and scope, which we confirm with the County.

What drives the cost

Repair sits at the low end; full replacement depends on the material you move to, the number of panels and elevations, how much water damage the tear-off uncovers, the amount of trim and re-flashing, and access on larger or hillside lots. Re-installing T1-11 is the least expensive replacement; fiber cement the most. We price the actual building after we see it.

FAQ

Can T1-11 be repaired, or does it all have to come off? If the failure is localized — a few panels at a splash zone with dry substrate behind — a targeted repair and repaint can work well. Widespread delamination or water that has reached the substrate points to replacement. We assess before recommending.

What should I replace old T1-11 with? The two most common upgrades are fiber cement and LP SmartSide engineered wood — both far more tolerant of missed maintenance than plywood siding. Fiber cement is also noncombustible, which matters for foothill parcels. If you want the original rustic look, we can re-side in fresh, properly sealed T1-11.

Why does T1-11 keep failing on my house? Almost always because the paint film broke down and water got into the edges and grooves. Under Alamo's hot, sunny summers a lapsed repaint is the usual culprit. Once water is in the plies, the panel swells and delaminates.

Do I need a permit to replace siding in Alamo? Yes. Alamo is unincorporated, so the permit and inspections go through Contra Costa County's Building Inspection Division. We handle it.

Get your Alamo T1-11 looked at

Call (415) 619-5167 or request a bid. We serve Alamo and the wider Contra Costa area — see finished work in our project gallery. Considering an upgrade? Compare fiber cement, LP SmartSide, and wood siding, or read Alamo siding replacement.