How site plan decisions affect TCAC scoring, C.3 stormwater on tight infill lots, parking reductions under AB 2097, ADA compliance, and the 18–24 month...

Affordable housing in California rides on TCAC scoring, C.3 compliance, AB 2097 parking reductions, and an 18-to-24-month funding cycle that punishes any civil surprise. The site plan has to earn every TCAC point on the checklist while staying buildable on an infill lot.

Density and Site Coverage

Multifamily site planning starts with the density calculation. How many units can the zoning allow? What's the maximum lot coverage? How much open space is required? These numbers set the upper bound on what the architect can design, and they cascade directly into the civil engineer's scope: more units means more parking, more impervious surface, more stormwater treatment, more utility demand, and more grading complexity.

On typical Bay Area infill sites — quarter-acre to half-acre parcels in established neighborhoods — the density bonus law (Government Code 65915) is often the mechanism that makes the project financially feasible. A density bonus allows 20–50% more units than the base zoning in exchange for affordable housing commitments. From the civil engineer's perspective, the bonus units add load to every system: water, sewer, storm, electrical, and parking.

Parking and Access

Parking is the most space-intensive element of a multifamily site plan. At 1.5 spaces per unit — a common suburban requirement — a 60-unit project needs 90 parking spaces. At 300 square feet per space (including drive aisle share), that's 27,000 square feet of paving: nearly two-thirds of an acre dedicated entirely to car storage. On a tight site, parking often dictates the building footprint more than the architecture does.

AB 2097, effective January 2024, prohibits cities from imposing minimum parking requirements on projects located within a half-mile of a major transit stop. This has transformed site planning for transit-adjacent projects in the Bay Area: without a parking mandate, the site plan can prioritize open space, stormwater treatment, and building coverage over parking. But even with reduced parking, some spaces are still typically provided, and each one needs to meet dimensional, accessibility, and EV readiness requirements.

Stormwater on Tight Sites

C.3 compliance on a multifamily infill site is one of the most challenging aspects of the civil design. The impervious area ratio is often 75–90%, which means the bioretention treatment area (at 4% of impervious) is 3–4% of the total site. Finding room for a bioretention basin that's large enough to treat the required area, receives runoff by gravity, and doesn't conflict with foundation setbacks or utility corridors requires careful coordination with the architect and landscape architect from day one.

Flow-through planters along building frontages are a common solution on constrained multifamily sites. They treat runoff from the adjacent roof and sidewalk, occupy linear space that would otherwise be landscape buffer, and can be integrated into the architectural aesthetic. The civil engineer designs the planter dimensions, media depth, underdrain system, and overflow connection; the landscape architect selects the plants and surface treatment.

Utility Coordination

A 60-unit multifamily building needs domestic water, fire service, sanitary sewer, storm drain, gas, electrical, and telecom. Each utility has its own lateral from the street, its own meter or point of connection, and its own set of design standards. On a 40-foot-wide street frontage, fitting all of these laterals without violating the minimum horizontal separation requirements between utilities is a spatial puzzle that the civil engineer solves on the composite utility plan.

The Bottom Line

Every project has its own constraints — site geometry, soil conditions, agency jurisdiction, schedule pressure. What doesn't change is the physics: water flows downhill, utilities need clearance, and code requirements aren't negotiable. The projects that go smoothly are the ones where the civil engineer is involved early enough to shape the site plan around these realities rather than retrofitting solutions after the architecture is locked.

At Calichi Design Group, we've built our practice around getting these details right the first time. Our team has permitted projects in dozens of jurisdictions across the West Coast and Pacific, and we know which agencies want what, which reviewers flag what, and which shortcuts actually cost more time than they save.

If you're starting a project and want to avoid the most common civil engineering pitfalls, reach out for a conversation. We'll give you an honest assessment of what your site needs and a fixed-fee proposal — usually within a week.