A homeowner reads that their district requires 10,000 square feet per lot, checks the county record, and finds their own lot is 8,059. The obvious conclusion is that splitting it is off the table. The obvious conclusion is wrong, and the reason is that two different minimums are in play.
Short answer: The district minimum for this zone is 10,000 square feet (14.04.010), and this lot is already below it. But an urban lot split runs on its own numbers: each resulting parcel must be at least 1,200 square feet, and one of the two may not be smaller than 40 percent of the original (15.155.030). On 8,059 square feet, both tests are met with room to spare.
The property
| Item | Value |
|---|---|
| City | San Rafael |
| Lot area | 8,059 square feet |
| Zoning district | R10, single family residential |
| Zoning source | MarinMap, the official regional GIS |
The assessor record for this parcel carries no lot dimensions or building detail, so this analysis works from lot area alone. That is enough for the split question, which is entirely an area test.
Key numbers
| Standard | Requirement | Applied to this lot | Source |
|---|---|---|---|
| District minimum lot area | 10,000 square feet | lot is 8,059, below it | 14.04.010 |
| Urban lot split, minimum per parcel | 1,200 square feet | both parcels clear it easily | 15.155.030 |
| Urban lot split, size balance | one parcel at least 40 percent of the original | smaller parcel at least 3,224 square feet | 15.155.030 |
| Zones where splits are allowed | R2a, R1a, R20, R10, R7.5, R5 | R10 qualifies | 15.155.030 |
| Use of new parcels | residential only | residential | 15.155.030 |
| Rental term on new units | longer than 30 days | no short term rentals | 15.155.030 |
Two minimums, two jobs
The 10,000 square foot figure is the district standard, and it describes the kind of lot the zone was drawn around. The urban lot split provisions set a different floor for parcels created by a split, and the code lists the qualifying zones by name — R10 among them (15.155.030).
Work the arithmetic on this lot:
- 40 percent of 8,059 square feet is 3,224 square feet, so the smaller of the two parcels cannot fall below that
- the widest permissible split is therefore about 3,224 and 4,835
- an even split lands near 4,029 and 4,030
- both ends of that range sit far above the 1,200 square foot floor
So the binding constraint here is the 40 percent balance rule, not the minimum size. On a lot this size the floor never comes into play; it would only start to matter on a parcel under 3,000 square feet.
What comes with the split
Three conditions travel with it and are easy to miss. The new parcels are limited to residential uses. Any unit created through the split must be rented for terms longer than thirty days, which rules out short term letting — and that restriction applies retroactively to an existing accessory unit on a parcel that later uses these provisions. And accessory dwelling units remain available on the new parcels, with a permit issued before July 18, 2022 for a house with an accessory unit not by itself preventing an applicant from developing two units (15.155.030).
One provision is worth knowing before anyone worries about the existing house: no setback is imposed for a structure that already exists, or for one rebuilt in the same location and to the same dimensions (15.155.030). A split does not force the current house to move.
Where the ordinary standards still apply
The lot split chapter states that the applicable objective development standards in the zoning and subdivision titles continue to apply to an urban lot split. San Rafael also allows measured relief from some of them — the maximum lot coverage may be increased by up to 10 percent of the lot area where that is necessary for significantly improved design, and a single family residence may add up to 100 square feet of floor area in conjunction with such a request (14.24.020).
What this does not settle
Whether a particular parcel qualifies depends on tests this analysis does not reach: prior subdivision history, whether the owner intends to occupy, the presence of protected tenancies, and site conditions such as flood or fire hazard mapping. Frontage, access and utility connections for a new parcel are separate questions again. Nothing here is a determination that a split will be approved — only what the written standards ask of a lot this size. Confirm with San Rafael planning. The San Rafael overview collects the rest.
