If your Moraga home went up in the postwar tract era, there is a good chance parts of it are clad in T1-11 — the grooved plywood or OSB panel siding that defined mid-century and 1970s construction. It was inexpensive, went up fast, and gave a home that vertical, woodsy look. It is also the cladding we are most often called to deal with in this town, because when T1-11 is not kept sealed and painted, it swells, delaminates, and rots from the bottom courses up. Bay Area Siding Company is a Larkspur-based siding and window contractor, and most T1-11 conversations in Moraga are really about what to replace it with. This page covers both paths.

Call (415) 619-5167 or request a bid.

How T1-11 fails on a Moraga home

T1-11 is a wood-based panel, and its weakness is water. Moraga's shaded canyon draws and north walls hold moisture well into spring, and the panel bottoms, the grooves, and the T-joints are where it shows first: soft edges, dark staining, plies separating, and a screwdriver that sinks into what should be solid. Once a panel has delaminated it cannot be sealed back to health — that section is spent. The telltale sign a homeowner notices is paint that will not hold along the lower courses no matter how often it is redone, because the substrate underneath is already moving.

Path one: replace failing T1-11 with a modern material

For most Moraga homes at the re-side stage, the sensible move is to retire the T1-11 and step up to a material that does not depend on perfect paint maintenance to survive:

• Fiber cement — noncombustible and rot-proof, the common answer on Moraga's hill and wildland-edge parcels (more on that below).
• LP SmartSide engineered wood — keeps a warm wood look and a paintable surface, lighter and far more decay-resistant than the original panel, and available in vertical panel profiles that preserve the T1-11 aesthetic if that is the look you want.

Either way, tear-off is the moment to see what the panel was hiding: we remove the old siding to the sheathing and substrate, inspect and renew the water-resistive barrier and flashing, and only get into the framing if the sheathing itself has rotted — a larger scope we would flag before proceeding.

Path two: re-install T1-11 where the rustic look is wanted

Sometimes the T1-11 look is the point — on a cabin-style home, a detached studio, an ADU, or a shed where budget and a deliberately rustic vertical panel are the goal. We do install new T1-11 in those cases. The non-negotiable is finishing: it has to be primed on all edges and faces and kept sealed and painted on a real schedule, or it will start the same failure cycle. We will be straight with you about that commitment before we hang the first panel.

The fire consideration on Moraga's hills

Moraga sits in the Moraga-Orinda Fire District, and the eastern and northeastern hills and open-space-adjacent parcels fall within the fire hazard severity zones on the updated 2025 Cal Fire maps. T1-11 is combustible wood-based panel; on a parcel carrying a fire-hazard designation, California Building Code Chapter 7A can govern the materials allowed on regulated exterior assemblies, and there noncombustible fiber cement is usually the right replacement rather than new T1-11. Whether Chapter 7A applies to your address depends on the parcel and scope, which we confirm with the Town and the fire district before speccing.

Permits and cost

Permits run through the Contra Costa County Department of Conservation and Development, with Town Planning or Engineering sign-off on most exterior work; we coordinate it. Cost depends on whether you are replacing with a new material or re-installing panels, how much substrate and framing repair the tear-off reveals (T1-11 failures often mean more hidden damage than expected), the number of stories and elevations, and hillside access. We price the actual home.

FAQ

Can you just replace a few bad T1-11 panels? Sometimes, if the failure is isolated and the rest is sound and well-sealed — but on a home where the paint won't hold along the lower courses, spot repairs usually chase a problem that keeps moving. We will tell you honestly whether a patch or a full re-side is the better spend.

What should I replace old T1-11 with? Most Moraga homeowners move to fiber cement (noncombustible, rot-proof) or LP SmartSide engineered wood (warm wood look, paintable, far more decay-resistant). If you want to keep the vertical panel look, both offer profiles that get you there without the original panel's fragility.

Can I keep the T1-11 look? Yes — either by re-installing new T1-11 (which must be primed all around and kept painted on schedule) or by using an engineered-wood vertical panel that mimics it with much less maintenance. On a fire-designated hillside parcel, we would steer you to a noncombustible option.

Does a T1-11 re-side need a permit in Moraga? Plan on it. Review runs through the Contra Costa County Department of Conservation and Development, with Town Planning or Engineering sign-off on most exterior work. We handle the paperwork.

Start your Moraga T1-11 project

Call (415) 619-5167 or request a bid. We serve Moraga and the wider Contra Costa area — see finished work in our project gallery. Weighing replacements? Compare fiber cement, LP SmartSide, and wood, or start at Moraga siding replacement.