In Hillsborough, the Renovation Ceiling Bites Hardest on the Lots You Can Actually Buy

Look at four projects that came before Hillsborough's Architecture and Design Review Board on the same night this March, and a pattern shows up that no listing sheet will ever mention. A 1985 Mediterranean on a 67,668 square foot lot proposed a renovation and new basement that would bring the home to 13,589 square feet, using roughly 94 percent of the 14,506 square feet the town would allow on that parcel. Two unrelated teardown proposals, on lots of 23,285 and 28,378 square feet, landed within a hair of each other at 24.97 percent and 24.9 percent floor area ratio. A fourth, on a much larger parcel implied by its own numbers to run around 62,700 square feet, proposed a rebuild using just 6.4 percent of the lot.

The pattern is not about architecture. It is about where the ceiling actually presses. On the biggest estate lots, the town's floor area limit barely enters the conversation, because the house a family wants to build doesn't come close to the cap. On the mid-size lots, the ones that make up a meaningful share of what actually trades hands in Hillsborough, that ceiling is often the first real constraint on the project, tighter than the budget and tighter than the architect's imagination.

That distinction matters for anyone shopping a Hillsborough property with renovation or rebuild potential in mind. The question is not whether you can afford the addition. It's whether the parcel has room left to grow into.

What one March agenda night made visible

The Architecture and Design Review Board's public agendas are a matter of record, and the Town of Hillsborough publishes them ahead of every hearing. Here is what came before the board on March 2, 2026, laid out plainly:

Three of these four are full demolitions of mid-century ranch homes, which tells its own story about what's aging out of Hillsborough's housing stock right now. But the number worth sitting with is the floor area ratio column. Two projects on similarly sized lots converge on almost exactly one quarter of the parcel, whether that's the legal ceiling or simply where two separate architects independently decided to stop. The project on the largest lot doesn't come close to that ratio, because the house the owner wants doesn't need to.

Why the ceiling moves with the lot, not the price

If you're comparing two Hillsborough listings on the assumption that the pricier one has more room to build, the FAR math says otherwise. A 67,668 square foot lot with an existing 8,820 square foot home already sitting at 94 percent of its allowed floor area has almost no expansion room left, regardless of what the current owner paid or what a buyer might be willing to spend on construction. A more modestly priced lot in the 23,000 to 28,000 square foot range, occupied by a dated ranch home under 4,000 square feet, may have far more legal room to grow into, even though the purchase price looks like the more attainable option on paper.

This is worth knowing before you fall for a listing's photos of a "great bones" ranch on a big parcel. The size of the lot tells you the ceiling. The size of the existing house tells you how much of that ceiling is already spoken for. The gap between the two is the only number that actually determines whether your renovation dream is a permit application or a fantasy.

It's also worth knowing that Hillsborough moved early to keep this math from changing much. In December 2021, ahead of California's SB9 taking effect on January 1, 2022, the town adopted objective development standards for building size, lot coverage, setbacks, and height specifically to apply before the state law arrived. SB9 opened the door statewide to splitting single-family lots into two parcels with two units each. Hillsborough's large minimum lot sizes and its own standards mean that door stays narrow here compared to denser Peninsula cities. For most buyers, the realistic play on a Hillsborough parcel is renovating or rebuilding within the existing lot, not subdividing it, which makes the floor area ceiling the number that actually governs your options.

The clock nobody puts on the listing sheet

Even once the FAR math works in your favor, Hillsborough's process runs on a calendar that has almost nothing to do with how good your architect is. A few mechanics worth knowing before you write an offer with renovation plans in mind:

1. Additions over 500 square feet, second-story additions of any size visible from the public right of way, and any new house all require a hearing before the five-member ADRB, a volunteer board appointed by the City Council whose members typically bring design or construction backgrounds. New houses need a preliminary review before a formal application can even be submitted.
2. Story poles marking the proposed building's bulk and roof heights must go up at least two weeks before the hearing, and a licensed surveyor or civil engineer, not the project architect, has to certify within five days that they're installed to plan.
3. The town mails public notice to every property owner within a 500-foot radius, 15 days before the scheduled hearing.
4. If the board approves the project, the story poles have to stay up through a 15-day appeal window, and come down no later than 20 days after the board's final action. If a project gets continued more than three weeks, the poles come back down and have to be recertified before it returns.
5. Miss any of these deadlines and the project doesn't get pulled forward. It gets pushed to the next available meeting.

That last point is the one that actually costs people time. The ADRB doesn't meet every week or even every month. Its 2026 calendar runs January 26, March 2, April 6, May 4, a cancelled June 1, June 15, August 3, August 31, October 5, a November date still pending, and December 7. There is no meeting at all in February. There is no meeting at all in July. As of this writing in mid-September, the board's next scheduled hearing is October 5, more than a month after its last one on August 31.

None of this is a reflection of how contentious a given project is. It is simply the structure of the calendar, and it means the honest answer to "how long before I can start construction" starts with counting how many hearing dates stand between you and approval, not how many weeks your contractor needs to draw plans.

What this means before you write an offer

If a Hillsborough property is appealing partly because of what you could build on it, a few questions belong in your due diligence alongside the inspection and the disclosures:

• What is the lot's actual floor area ratio ceiling, and how much of it does the current structure already use? A call to the Planning Division, where ADRB-level and administrative-level applications route to different staff contacts such as Liz Ruess and Cynthia Richardson, can get you the specifics for a given parcel before you write an offer contingent on renovation potential.
• Does your planned addition trigger a full ADRB hearing, or does it qualify for administrative review? Minor additions under 500 square feet with no change to architectural style or exterior materials can often be approved by staff directly, without a public hearing or the 500-foot notification radius, and frequently without story poles. That distinction alone can be the difference between a project measured in weeks and one measured in seasons.
• Does the current listing's price reflect a lot with real room left under the ceiling, or one already built out close to its legal maximum? Two homes at the same price point can have entirely different renovation futures depending on where that math lands.

A few questions worth asking before falling in love with the potential

Does every home addition in Hillsborough need to go before the board? No. Minor additions under 500 square feet that don't change the architectural style or exterior materials can be approved administratively by Planning staff. Anything larger, any second story visible from the street, and any new house requires the full ADRB process with a public hearing.

How long do story poles actually have to stay up? At minimum, two weeks before the hearing through the 15-day appeal period afterward, and they must come down within 20 days of the board's final decision. If the project gets continued for more than three weeks, the poles go back up and get recertified.

What happens if I miss a filing deadline? The application doesn't lose its place in line so much as it loses its date. An incomplete submission gets pushed to the next meeting the board has scheduled, which given the calendar's gaps can mean waiting well over a month for the next opportunity.

Renovation potential is one of the more genuinely useful things a builder's eye can tell you before you're locked into a Hillsborough purchase. Working through the framing, the additions, and the remodels that actually get through this town's process has shaped how Julie Baumann Homes looks at a listing's real upside, not just its curb appeal. If you're weighing a Hillsborough property with a project in mind, Let's Connect before you write the offer, not after.