San Ramon T1-11 Siding

T1-11 is the grooved vertical panel siding that shows up on a lot of San Ramon homes built in the 1980s and 1990s. You see it on original siding in the established neighborhoods off Bollinger Canyon Road, on garage walls and side elevations, and on fences and sheds throughout the valley. It was economical and quick for builders, and it gives a clean, slightly rustic vertical-groove look. After a few decades of valley sun and sprinkler overspray, though, it tends to give out in predictable ways.

Bay Area Siding Company is a Larkspur-based siding and window contractor. We handle T1-11 in both directions: tearing out failing panels and replacing them with a more durable material, or re-installing new T1-11 where the grooved look is what you (or your HOA) want.

Get a straight assessment: call (415) 619-5167 or request a bid.

How T1-11 fails on a San Ramon house

T1-11 is a plywood or OSB panel with grooves milled into its face. It is essentially engineered wood sheet goods, and it stays healthy only as long as its paint or stain film keeps water out. Once that film breaks down, the panel starts absorbing moisture at its weakest points. On San Ramon homes, the common failure points look like this:

• Swollen, flaring bottom edges. The lower cut edge of each panel wicks water from irrigation and wet-season runoff. It puffs up, splits, and eventually crumbles near the foundation line.
• Delaminating plies. On plywood versions, the face veneer lifts and separates in patches, often starting at the grooves where paint is thinnest.
• Paint that won't stay put. The south- and west-facing walls take the brunt of the long, dry summers, and the grooves shed paint faster than flat surfaces do. Some owners find they're repainting the same wall every few years.
• Soft spots at sprinkler height. A lawn head that has hit the same panel for twenty-plus years can leave that section spongy to the touch.
• Seams and vertical joints opening up. Gaps at the panel butt joints and trim let water get behind the face.
• Woodpecker and insect damage. Soft, weathered panels are easy targets.

A single damaged panel, caught early, can sometimes be cut out and patched. When the swelling and delamination repeat around the house, patching turns into a loop, and replacement becomes the better investment.

The technical point most T1-11 quotes skip

This matters more with T1-11 than with almost any other siding. T1-11 is often installed as a combination siding-and-sheathing panel. The rated panel is nailed directly to the wall framing and serves as both the exterior finish and the wall's bracing, with no separate sheathing layer behind it. On other homes, it was installed over sheathing like any ordinary cladding. You can't tell which you have from the curb.

That difference changes the scope:

• T1-11 over separate sheathing. Removing the panels works like a normal re-side. The old cladding comes off to the sheathing/substrate, we inspect and correct the water-resistive barrier (WRB) and the flashing at windows, doors, and penetrations, and the new siding goes on.
• T1-11 as the only layer. Removing the panels opens the wall to the framing. In that case, new structural sheathing typically has to go on first, because the old panels may have been providing the wall's bracing. Then come the WRB, the flashing, and the new siding. This is a larger job, and the structural requirements are something we confirm with the building department instead of assuming.

We check this during the site visit, usually by looking at an exposed edge, an attic or garage wall, or a small inspection opening. That way your bid reflects the real scope, and you don't get a mid-project change order.

What to replace T1-11 with

You have real options, and the right one depends on budget, the look you want, and what your HOA allows.

• LP SmartSide. This engineered wood is treated to resist moisture and decay, and it's offered in panel and lap profiles. It's the natural step up for owners who like T1-11's wood character and want much better durability. It still needs periodic painting.
• Fiber cement, including James Hardie. Fiber cement is noncombustible, rot- and pest-resistant, and stable under heat and UV. It comes in vertical panel or board-and-batten styles for a similar look, or lap siding if you want a change. A factory finish like Hardie's ColorPlus can also simplify HOA color matching. Details are on our San Ramon James Hardie page.
• Vinyl. Vinyl is the lower-maintenance, budget-conscious choice where the association permits it. In strong sun, pick colors and lines carefully.
• Wood. Natural board-and-batten or cedar is premium and repairable, but it carries the most upkeep.

When putting T1-11 back makes sense

Sometimes the right answer is new T1-11. Examples include matching an addition or garage wall to the rest of the house, or keeping a consistent look within a community. Modern panels installed correctly hold up far better than the originals did. "Correctly" means:

• over a proper WRB, with flashing at every opening
• with sealed, primed edges, especially the bottom cut
• with Z-flashing at horizontal joints
• with adequate clearance above grade and hardscape
• finished promptly and kept painted

We'll also point out the trade-off honestly. Even done well, T1-11 asks more of you over time than fiber cement or treated engineered wood.

San Ramon approvals: HOA first, then the City

Many San Ramon homes sit within a homeowners association, including Gale Ranch, Windemere, and the broader Dougherty Valley communities. Association architectural guidelines typically control exterior materials, profiles, and color. If you're changing from grooved panel to lap siding, or from a stained finish to a painted one, expect the review committee to want to see it. We prepare material and color specs with that review in mind.

The building permit side runs through the City of San Ramon Building and Safety Services division (Community Development). We confirm the permit scope for your project with the city. That's especially important when a T1-11 removal requires new structural sheathing.

Fire exposure depends on the parcel

T1-11 is a wood product, so it's combustible. Most of San Ramon is valley floor that generally falls outside higher fire hazard severity zones. Some parcels along the eastern Tassajara hill edges, however, can fall within higher-hazard zones on maps maintained by the San Ramon Valley Fire Protection District. Where a designation applies, California Building Code Chapter 7A can govern the exterior wall covering and may steer the choice toward noncombustible or ignition-resistant materials, such as fiber cement. Whether and how it applies depends on your parcel and the scope of work. We check the designation before recommending a material.

What drives the cost

We don't publish prices, because T1-11 jobs vary more than most. The biggest factor is whether the panels sit over sheathing or serve as the sheathing, since new structural sheathing adds material and labor. After that, cost depends on:

• the replacement material and finish
• the square footage and number of stories
• how much trim, window, and door flashing work the walls need
• any localized damage found near leaky windows or sprinkler zones
• HOA profile or color requirements

We measure, inspect, and then price.

How the job goes

1. We assess the walls, confirm how the T1-11 was installed, and discuss materials.
2. We line up HOA approval and the city permit.
3. On install days, we remove the old panels and correct the WRB and flashing. We add sheathing where required and install and finish the new siding.
4. We finish with trim, sealing, and a walkthrough.

Replacing windows at the same time can make sense, since the openings are already exposed. See San Ramon window replacement. For the broader material decision, start with San Ramon siding replacement, browse our projects, or see other Contra Costa service areas.

FAQ

Can I just paint over my swollen T1-11? Paint can protect sound panels, but it won't reverse swelling or delamination. Once the bottom edges have flared or the plies are separating, the damaged material needs to come out. Paint over it only buys a little time.

Why might my T1-11 replacement need new sheathing? On many homes, T1-11 was installed directly on the framing as a combination siding-and-sheathing panel, so it may be part of the wall's bracing. Removing it can mean installing structural sheathing before the new siding. We confirm which case applies before bidding.

Will my San Ramon HOA let me switch from T1-11 to lap siding? It depends on your association's architectural guidelines. Some communities are flexible and others want the existing profile maintained. We can prepare the specs your committee needs to review, then coordinate the city permit.

Is new T1-11 a bad idea? Not necessarily. Installed over a proper WRB with sealed edges, flashing, and ground clearance, it performs far better than original builder installs. It still needs more maintenance than fiber cement or treated engineered wood, and it may not suit a parcel in a designated fire hazard zone.

Ready to deal with failing T1-11? Call (415) 619-5167 or request a bid.