Kentfield T1-11 Siding

T1-11 is the grooved plywood or OSB panel siding that went up on a lot of mid-century Kentfield homes, cabins, and outbuildings — vertical sheets with the reveal cut in to look like board-and-batten, fast to install and easy on a budget. Decades on, most of the T1-11 conversations we have in this valley are about what to do now that it's failing: reseal and keep it, or replace it with something that survives the climate better.

Bay Area Siding Company works with T1-11 across Marin from Larkspur, minutes from Kentfield. This page is the honest version of that decision. For the wider material picture — fiber cement, engineered wood, and the rest — see the Kentfield siding replacement overview.

Not sure whether yours is worth saving? Call (415) 619-5167 or request an estimate.

Why T1-11 struggles in this particular valley

T1-11 is wood, and wood panel siding lives or dies by its finish. As long as the paint or stain is intact and the top edges and joints stay sealed, it does its job. The moment water gets in — a failed bead of caulk, an unsealed cut edge, a top edge that wicks — the panel swells, the plies delaminate, and the grooves start to hold moisture.

Kentfield is about the hardest place in the Bay Area to keep T1-11 sealed. It records one of the region's highest annual rainfall totals, the creek-valley air stays humid, and the tree canopy throws deep shade that keeps north and creek-facing walls damp for days after a storm. That's exactly the environment that finds every unsealed edge. So the T1-11 that's coasting along in a dry inland town is often visibly delaminating here at the same age.

Repair, or replace?

Spot repair and refinishing can make sense when the panels are largely sound — solid, no delamination, no soft spots you can press into — and the problem is a tired finish or a few failed joints. We reseal edges and joints, replace isolated damaged sheets, and get it repainted. It buys years, and it's the budget path.

Replacement is usually the smarter money once the failure is widespread — swollen or delaminating panels, soft grooves, staining or musty smells on the interior walls behind them, or original panels simply at the end of their life. The common upgrade path in Kentfield is to replace failing T1-11 with a material that handles the moisture better:

• Fiber cement — noncombustible and dimensionally stable when damp; the strongest choice on a fire-exposed hillside parcel.
• LP SmartSide — engineered wood, treated against moisture and pests, keeping a warm wood look with far less fragility than plywood panel.

Some owners of cabins, sheds, or intentionally rustic homes want to re-install T1-11 for the look. We do that too — with the sealing, edge detailing, and clearances that give the new panels a fighting chance in this climate.

The fire angle on the slopes

On the wooded parcels toward Kent Woodlands, replacement carries an extra consideration. Those lots carry real wildfire exposure, and Cal Fire's updated Fire Hazard Severity Zone maps are moving through local review and adoption in Marin. Where a parcel falls under a fire-hazard designation, California Building Code Chapter 7A can favor noncombustible cladding — and plywood T1-11 is combustible. That's often the deciding push toward fiber cement on a hillside re-side. Whether Chapter 7A applies depends on your parcel and scope, so we confirm it with Marin County rather than assume. Kent Woodlands design review, through its property owners association, can also weigh in — flag it early.

How the work goes

On a replacement we remove the old panels to the sheathing and substrate, inspect and repair any concealed rot — common where T1-11 has been leaking — install a proper water-resistive barrier (many older panel-sided homes never had one), and detail the flashing at every opening, penetration, and transition for the valley's rainfall before the new cladding goes up. Framing is only involved if the sheathing itself has failed. Kentfield is unincorporated, so permitting runs through the Marin County Community Development Agency, Building and Safety Division at the San Rafael Civic Center. We handle it.

What affects the cost

We price after seeing the walls, not online. The variables: repair vs. full replacement, the size and height of the structure, hillside access, how much concealed rot appears once panels come off, the replacement material you choose, whether trim and windows are integrated, and any County or association review.

Frequently asked questions

Can my T1-11 be saved, or does it need to come off? It depends on condition. If the panels are solid and the problem is a worn finish or a few bad joints, we can reseal, patch, and repaint. If they're swollen, delaminating, or soft — common on older, frequently-wet Kentfield walls — replacement is the better investment.

What should I replace failing T1-11 with? Most Kentfield homeowners move to fiber cement or LP SmartSide. Fiber cement is noncombustible and best for fire-exposed hillside lots; SmartSide keeps a warm wood look with better moisture resistance than plywood panel. We'll compare them for your home.

Can I keep the T1-11 look? Yes — we can re-install T1-11 where you want the rustic panel look, on a cabin, shed, or home, with the edge sealing and flashing that help it last in this damp climate.

Does replacing T1-11 in Kentfield need a permit? Yes. Kentfield is unincorporated, so the work is permitted through the Marin County Community Development Agency's Building and Safety Division, and Kent Woodlands homes may also face design review. We manage it.

Get your T1-11 assessed in Kentfield

Call (415) 619-5167 or request an estimate. We'll tell you honestly whether to reseal or replace, weigh the upgrade materials against your exposure, and handle any fire or association review. See our project gallery and the Marin service area.