1. What Changed, in One Number
If you've priced out an SB 9 project in San José any time before this year, you were probably designing to a 0.45 Floor Area Ratio (FAR) — the standard planners used to cap how much floor area you could build relative to your lot size.
That number just moved. Under Ordinance No. 31298 (planning file PP25-001), which amends San José Municipal Code Chapter 20.30, the city raised the SB 9 FAR ceiling to 0.65. The ordinance text is direct: "the maximum Floor Area Ratio for each lot shall be 0.65, calculated in accordance with Section 20.100.1020."
Two things to be clear about before anything else. First, this is not a general loosening of single-family zoning. It only changes what you can build through the SB 9 process — a lot split, and/or adding a second unit under SB 9's ministerial approval. An ordinary remodel or room addition on a standard San José single-family lot still runs under the regular R-1 zoning standards, which this ordinance doesn't touch. Second, this is not a change to SB 9 itself. SB 9 is the 2021 state law that forces cities to ministerially approve those lot splits and second units — no discretionary hearing required. What San José changed is its own objective design standards, the local rules that govern how big SB 9 units can actually be. State law sets the floor; the city still writes the specific numbers, as long as they don't undercut what the state guarantees (more on that guarantee in Section 3).
2. The New Math: Floor Area and Lot Coverage
FAR math is simple once you see it: max floor area = FAR × lot area. Raising the multiplier from 0.45 to 0.65 raises the ceiling on every lot size. Take a 6,000-square-foot lot — a common size across San José's single-family neighborhoods:
| Metric | Old standard (0.45 FAR) | New standard (0.65 FAR) | Change |
|---|---|---|---|
| Max floor area (FAR × lot) | 2,700 sq ft | 3,900 sq ft | +1,200 sq ft |
That's the difference between a tight two-unit layout and genuinely comfortable square footage across a main house and a second unit. But floor area was never the only constraint SB 9 projects had to clear — Ordinance No. 31298 also added San José's first explicit SB 9 lot-coverage cap, in a new section, §20.200.675, tiered by lot size:
| Lot size | Max lot coverage |
|---|---|
| 1,200 – 2,500 sq ft | 75% |
| 2,501 – 9,000 sq ft | 65% |
| Greater than 9,000 sq ft | 60% |
For that same 6,000-square-foot lot (the middle tier), the coverage cap works out to 0.65 × 6,000 = 3,900 sq ft of footprint — the same figure as the new floor-area ceiling at that lot size. That match is a coincidence of this particular lot size, not a universal rule. The practical point: FAR and lot coverage are two separate ceilings, and a real project has to fit under both at once, along with everything in Section 4 below. A design that pencils on floor area alone can still fail on footprint.
3. Two More Rules Worth Knowing
The lot-split rule. SB 9's other headline feature — beyond adding a second unit — is the ministerial lot split: dividing one parcel into two. Municipal Code §20.30 subsection C.4 states: "Floor Area and lot coverage tabulation calculations shall apply to the entire undivided lot, irrespective of any subsequent subdivision into separate parcels." In plain terms: the FAR/coverage budget is calculated on the original, pre-split parcel — not recalculated fresh on each smaller lot after the split. Because FAR is a flat 0.65 either way, this doesn't change the floor-area math. Where it matters is coverage: without this rule, a smaller post-split lot could otherwise jump into a higher coverage-percentage tier just by being smaller. This rule closes that gap.
The 800 sq ft guarantee. This one's a protection, not a limit. Municipal Code §20.30 subsection C.3 states the FAR/coverage math "shall not preclude a second dwelling unit with a maximum eight hundred (800) square feet" on a lot with an existing or proposed dwelling. Even on a small lot where the math gets tight, the city can't use these standards to zone out an 800-square-foot second unit entirely — the same state-law-driven floor described in Section 1: San José sets its own numbers, but not so restrictively that they defeat what SB 9 is designed to allow.
4. Allowed ≠ Buildable — What Still Has to Fit
A 0.65 FAR is a ceiling, not a promise. It tells you the maximum floor area the code permits — it does not mean any given lot can actually build to that number. The real, buildable envelope on a specific parcel is the intersection of FAR and lot coverage and everything else that still applies to SB 9 projects in San José:
- Setbacks — including the 4-foot side/rear minimums referenced in the ordinance
- Height limits — 25 feet within the rear 20 feet of the lot
- Parking requirements
- Tree protection rules
- Fire-access requirements
On plenty of real lots, the 65% coverage cap or a setback will bind before the 0.65 FAR does. This ordinance raises the ceiling — it doesn't remove the walls.
5. What This Means If You Own or Are Buying a Lot in San José
If you're evaluating an SB 9 project — a lot split, a second unit, or both — on a San José parcel, two things follow directly from this change:
- Any feasibility study still using 0.45 FAR is out of date. The current ceiling is 0.65, and the coverage tiers above now apply where none did before. Have the numbers re-run against the current standard before you rely on them.
- More floor area on paper is not the same as more buildable house. Before you get attached to a design built around the new ceiling, confirm it against lot coverage, setbacks, height, parking, tree, and fire-access rules for your specific parcel — those haven't loosened.
If you're a buyer eyeing a San José single-family lot with SB 9 potential in mind, the same caveat applies in reverse: the theoretical envelope on a listing is larger than it was a year ago, but "theoretical" is doing real work in that sentence. Confirm actual buildable square footage with someone who's run the numbers against your specific lot, not the FAR alone.
Two scope reminders. These exact FAR and coverage numbers are San José's own local objective design standards, not the SB 9 statute — a neighboring city implementing SB 9 will very likely use different numbers, so don't carry this 0.65 across city lines. And because the ordinance took effect recently, don't assume every checklist or online resource has caught up yet; verify against the current Municipal Code rather than an older summary.
Sources: City of San José Ordinance No. 31298 (planning file PP25-001), amending Municipal Code Chapter 20.30 and adding §20.200.675 — staff memo and draft ordinance text, Legistar File #26-038. Retrieved via San José's Legistar system (library.municode.com and sanjoseca.gov blocked automated retrieval directly). Effective-date detail is approximate by design; verify current Municipal Code text before relying on any specific figure for a live project. This is general information, not project-specific feasibility advice — confirm setbacks, height, parking, tree, and fire-access requirements against your actual parcel before designing to these numbers.