My client had three days to decide on a 17,000 square foot lot in Mill Valley. With the approvals in the right order, the property can become two lots with up to 7,500 square feet of floor area, 50 percent more than the zoning allows as one lot.
What my client wanted
He had just won the lot, listed at $955K and bid past $1.7M in a single day. Two houses from the 1950s sat on it, one of 800 square feet and one of 1,200. He had three days to commit, with a five-figure deposit riding on the decision.
He called me with one question: what can SB 9 actually let me build on this lot?
The constraint
On paper it looked like a clean SB 9 lot split. But under certain conditions, SB 9 says you cannot demolish or alter the existing units on a property like this. “Demolish” is clear. “Alter” is not well defined anywhere. Can you add a window? Move a wall?
I went to the Marin County planning counter and put the question to them directly. Two planners gave me two different answers, so I asked for the county’s written policy, and they took the question to the community development director.
How I handled it
While that ran, I worked the ordinance from where my client wanted to end up. SB 9 lets the owner of a single-family lot split it into two lots, with two units on each lot, approved ministerially: the county checks the application against written standards, with no hearing.
The rule on altering the existing houses applies only once the lot becomes an SB 9 property. That makes the order of the steps the strategy:
Remodel and add onto the existing houses first, through standard design review.
Then split the lot under SB 9.
By the time the restriction applies, the work on the houses is already legal and finished.
The lot split is where the hidden value is. As a single lot in this zone, the property is allowed 5,000 square feet of floor area. Divided in two, each new lot would be allowed 2,500. Using in-depth knowledge of the county zoning ordinances and state law, there are procedural ways to develop it as two lots with up to 7,500 square feet of floor area and up to four units.
When I described the rule to the county as a hindrance, the planner corrected me, and he had it right:
“It’s not a restriction. It’s a grant. The whole thing is an allowance.”A Marin County planner
The result
Three days of research and phone calls. At the end my client had a clear answer, went ahead with the purchase and put his money down on solid ground.
Is this possible on your property?
What SB 9 can do on a lot is rarely visible from the listing. It depends on the zoning, what already stands on the lot, historic mapping and any recent tenancy history. A lot split also asks the owner to sign an affidavit to live there for three years. A thorough parcel review answers these questions, ideally before you commit.
Send me the address and your goals for the property. You will get a preliminary parcel review: which approval paths are open, roughly what each one yields in floor area, and the order of steps that gets closest to what you want. If you are a broker with a listing like this one, send me the listing and I’ll tell you what the lot allows.
Send me the address. I’ll tell you what the lot allows.
Send Scott the addressHow the ministerial path works
