Novato: building on adobe clay
Much of Novato sits on what longtime residents and builders call adobe, a dark, highly expansive clay. In winter it swells and seals. Rain that would soak into sandy soil sits on the surface or perches a few inches down. In summer it shrinks and opens cracks wide enough to lose a garden trowel in. Foundations on adobe ride that cycle every year. Cracked slabs, sticking doors, separating trim, and stair-step cracks in stucco are often more about soil moisture swings than about the foundation itself.
Good drainage on adobe is about consistency. Water should never pond against the foundation in winter, and it should be moved away in a controlled way instead of soaking the soil under one corner of the house. Downspouts are the first suspect. One leader dumping beside the footing can swell that corner of the house every storm. Running every downspout in a solid tightline to an approved outlet is often the single most valuable fix on a Novato lot.
Indian Valley & San Marin
The west Novato neighborhoods of Indian Valley and San Marin run from the valley floor up into the hills. Valley-floor lots tend to have flat, slow-draining adobe yards that stay soggy for weeks. Hillside lots get seasonal seepage moving downslope through the clay toward the uphill side of the house. Typical projects include:
- Perimeter French drains built for clay, with non-woven fabric, washed crushed rock, and rigid SDR-35 pipe
- Regrading and lowering planters so soil and hardscape slope away from the foundation
- Curtain drains on hillside lots, cut to the clay contact uphill of the house
- Crawlspace sump systems for raised-foundation homes where water collects under the house
Bel Marin Keys
Bel Marin Keys is a lagoon community built on reclaimed bayland east of Highway 101. Groundwater is shallow, the soils are soft bay clays, and gravity outlets are limited because there is very little elevation to work with. Water that collects under or around a home usually needs to be pumped out rather than drained. Outlet options are shaped by the community's lagoon and stormwater system, so check Bel Marin Keys Community Services District rules and Marin County permits before discharge is designed.
Tiburon Peninsula: steep bedrock view lots
The Tiburon Peninsula and Belvedere are built on steep Franciscan bedrock, including serpentinite exposed along the ridge around Ring Mountain. Thin soils over rock mean water runs off and through the hillside fast. It travels along fractures in the rock and along the contact between rock and the soil above, then shows up wherever a house is cut into the slope.
- Seepage from rock cuts. Lower levels, garages, and stem walls cut into rock often weep from the cut face after storms. Drainage placed directly against the cut, behind a waterproofed wall, captures that water before it reaches the interior.
- Tall walls and stacked levels. View homes typically depend on tall retaining walls and multi-level foundations, all of which need wall drainage to relieve hydrostatic pressure.
- Serpentine instability. Saturated serpentine soil is slick and prone to movement, so trench design, filter fabric, and outlet locations need care.
- Engineering and permits. Steep lots and deep excavation frequently require geotechnical review and a permit from the Town of Tiburon or City of Belvedere.
Discharge on the peninsula should almost always be piped in closed, solid lines down to the street or an approved storm connection. Releasing concentrated water onto a steep, rock-and-serpentine slope is one of the fastest ways to start erosion on your lot or the one below it.
Corte Madera: Christmas Tree Hill & the bayside flats
Christmas Tree Hill rises steeply above central Corte Madera, with view homes on narrow, winding streets and lots stepped into the hillside. Drainage issues here look like the peninsula's: water moving downslope through shallow soil over rock, seepage against uphill foundation walls, and old retaining walls with little or no drainage behind them. Tight streets and steep driveways often mean hand trenching and careful staging.
Downhill, Corte Madera's neighborhoods near the bay marsh have the opposite problem: shallow groundwater, slow-draining bay soils, and street drainage that can back up during king tides and heavy storms. Crawlspace dewatering with a sealed sump and battery backup, plus pumped discharge with a check valve, is the standard approach. Curb cores and street work need an encroachment permit from the Town of Corte Madera.
Seeing cracks, seepage, or standing water? Call (415) 555-0100 or request an estimate from a local drainage specialist.
Drainage services in Novato, Tiburon & Corte Madera
- Hillside French & Curtain Drains → Deep interceptor curtain drains, French drains, and downspout tightlines designed for Marin clay and serpentine slopes.
- Crawlspace Waterproofing & Sump Pumps → Interior perimeter drains, cast-iron sump pumps with battery backup, and reinforced vapor barriers for wet Marin crawlspaces.
- Retaining Wall Drainage → Back drains, weep hole relief, and pressure relief for leaning or weeping hillside retaining walls.
Frequently asked questions
What is adobe clay and why does it matter for my Novato foundation?
Adobe is the local name for highly expansive clay soil. It swells when wet and shrinks and cracks when dry. Foundations on adobe move with those cycles, so the goal of drainage is to keep moisture around the foundation consistent: no water ponding against it in winter, and no soil pulled bone-dry by thirsty plants in summer.
Can a French drain fix soggy yards in San Marin or Indian Valley?
Yes, if it is built for clay. Adobe seals ordinary pea-gravel drains quickly. A durable drain uses non-woven filter fabric, washed crushed drain rock, rigid perforated PVC with consistent fall, and cleanouts. Most importantly, it needs a real outlet, because a drain with nowhere to go just stores water in the trench.
My Tiburon home is built on rock. Why is there water in my lower level?
Bedrock is rarely solid. Franciscan rock on the peninsula is fractured, and water travels along those fractures and along the contact between rock and the soil above it. Where a lower level or garage is cut into the hillside, that water seeps out of the cut face. Drains placed against the rock cut, plus a sump where gravity outlet is not possible, are the usual fix.
Do Tiburon and Belvedere hillside drainage projects need engineering?
Many do. Steep view lots, tall retaining walls, and excavation near foundations on slide-prone slopes often need a geotechnical or civil engineer, and a permit from the Town of Tiburon or City of Belvedere. Your contractor should tell you at the site visit whether engineering is likely.