Geological diversity — fill vs bedrock
SF has wildly varied soil. Bedrock in Pacific Heights, Russian Hill, Twin Peaks, parts of Bernal Heights and Glen Park. Engineered fill in SOMA and Mission Bay. Man-made fill in the Marina (much of it 1906 earthquake debris, which is why the neighborhood liquefied in Loma Prieta). Reclaimed marshland in parts of Mission and the Western SOMA. For foundation work, geology dictates everything: a Pacific Heights foundation repair is straightforward; a Marina foundation requires structural review of the surrounding fill before anyone sets a footing. We map the soil before we map the scope.
Building stock by era
Pre-1906 survivors are rare in the central city — most of what wasn't burned in the fire was rebuilt after. Post-1906 to pre-WWII is the vast majority of SF housing stock: balloon-frame construction, unbraced cripple walls, no anchor bolts, original concrete now nearing a century in service. Post-WWII tract construction defines the western Sunset and parts of the Excelsior; mostly slab-on-grade. Modern construction (1990s and later) is code-compliant and rarely needs structural retrofit. We work all four eras regularly and the bid changes meaningfully with the construction date.
DBI & permitting specifics
SF DBI is rigorous but workable when the paperwork is in order. The Mandatory Soft Story Retrofit Ordinance — wood-frame buildings with five or more residential units and two or more stories over a soft or weak story (typically ground-floor parking or open lobby), permitted before January 1, 1978 — has been mandatory for affected owners since the 2013 ordinance. The Hillside Development Ordinance triggers on steep slopes. Existing-conditions surveys are non-negotiable for additions. Many SF buildings are condos or co-ops where board approval is needed in addition to DBI; we provide paperwork-ready packets including scope, schedule, hoist plans, and neighbor-notice templates. Treating the board as a stakeholder rather than an obstacle saves weeks.
Seismic priorities for older homes
Cripple-wall bracing and anchor bolting are baseline retrofit work for any pre-1980 SF home. Soft-story shear panels are required for buildings under MSSP. Hold-downs at shear walls become critical on hillside lots in Bernal Heights, Twin Peaks, and Glen Park, where lateral loads work harder against the structure. Brick chimneys are a common SF seismic risk; we coordinate with chimney specialists when the engineer's plans call for bracing or replacement. We do not bundle chimneys into structural retrofits unless the drawings explicitly require it.
Hillside neighborhoods & access
Bernal Heights, Glen Park, Twin Peaks, Russian Hill, Pacific Heights, Cole Valley — common retaining wall, foundation, and underpinning work. Soils plus slope plus tight access make these jobs longer than nominal. We can typically reach 90% of SF hillside lots with a small-equipment plan: mini-excavator, walk-behind compactor, concrete pumped from the street where access is too tight for a chute. Where equipment can't reach, we hand-dig. It costs more; we'll be specific in the bid. Parking permit windows, neighbor notification timing, and DBI rough-inspection scheduling on these lots all matter — we coordinate the plan before crews mobilize, not after a neighbor complaint stops the day's work. The result is hillside jobs that finish on the calendar we set, not the calendar your neighbors set for us.
Drainage & atmospheric rivers
SF rainfall is concentrated. Atmospheric river events overwhelm older drainage systems and reveal which retaining walls have working daylight outlets and which were back-built without drainage paths. Every wall we build in SF gets gravel backfill, perforated drain pipe, geotextile fabric, and a daylight outlet sized for the storm event, not the average. The same approach applies to slabs near downhill structures — drainage tie-ins designed for the once-in-five-year event, not the median.
