In Hillsborough, a Lot's Maximum Square Footage Is a Ceiling, Not a Promise. This Year's Design Review Record Shows Why

On April 6, 2026, Hillsborough's Architecture and Design Review Board voted on a new Modern home at 2555 Summit Drive. The design would have replaced a 1968 single-story ranch of about 4,100 square feet with a 7,915-square-foot house on a 40,762-square-foot lot. The lot's maximum was 10,190 square feet, so the proposal sat more than 2,000 square feet under the limit. The motion to approve still failed, 2 to 3.

The board then voted unanimously to continue the project "to address massing and visual prominence." Members had discussed a 70-foot frontage and its effect on the feel of the street, along with the height and how the house would sit next to its neighbor. The house was approved four weeks later on a 3 to 2 vote, after the architect revised the design. That made three meetings across roughly three and a half months.

That one project explains a lot about pricing an older Hillsborough home. If part of the price rests on what could be built there, the useful figure is what the board approved on lots like it this year. The maximum the zoning formula allows is a different and larger number.

The Town has already told buyers this

Hillsborough's Development Standards, revised July 2026, set maximum house size at 25 percent of net lot area for the first acre, plus 15 percent of net lot area beyond one acre. That formula is how a listing gets to its "could build up to" figure. The same document then warns against relying on it:

"The ADRB cautions prospective buyers from purchasing a home based on the assumption that the maximum permitted square footage (based on these standards) can be built."

The standards add that a project nearing the 25 percent ratio may be judged "too massive or too bulky." They also say the board expects more architectural quality and detailing from larger houses. Every exterior change in town goes through design review, including re-roofing, fencing and color changes. New houses, major remodels and teardowns also need a preliminary review before a formal hearing.

The Residential Design Guidelines chapter on design review lays out the sequence. Applicants speak with a planner first and notify adjacent owners. Plans and the fee are due at least 10 full working days before the requested meeting. Formal review is a public hearing, and its outcome can be appealed to the City Council. An approval lapses if no building permit is issued within one year, with one possible one-year extension.

What 2026's approvals actually looked like

The Town's approved meeting minutes show how far apart the formula and the approved house can be, and how long it takes to close that gap.

At 2555 Summit, the approved house used about 78 percent of the lot's stated maximum. At 210 Uplands Drive, the approved 14.35 percent ratio is well below the 25 percent rate that applies to a lot's first acre. Even the fastest approvals in the table took several months from first review to final vote. Pinehill took about six months, and its approved house grew from the 4,012 square feet shown at preliminary review.

None of these projects asked for the maximum, and the board still sent two of them back. A buyer who prices a lot at its full formula figure is assuming a result this year's record does not show.

What sent projects back

The continuances and critical comments in 2026 came from a short, repeated list of concerns, and almost none of them involved square footage:

• Massing and visual prominence. This was the stated reason 2555 Summit Drive was continued in April.
• Neighbor privacy and screening. 210 Uplands Drive was continued in June so the applicant could revise the landscape plan after neighbors raised screening and privacy concerns. It was approved in August on condition that the first phase of planting go in before construction.
• A clear architectural style. The second-story addition at 3 Sherwood Court was continued on Aug. 31. The board asked for a clearer architectural character because the design read as partly modern and partly farmhouse. It was listed for continued formal review on the Oct. 5 agenda.
• Garages and parked cars. At 2480 Summit Drive, a teardown proposed for a new Modern home of about 5,524 square feet, the board was generally unsupportive at its August preliminary review. Members cited a front-facing garage, the massing, an unclear style and a design that felt commercial rather than residential. At 715 Brewer Drive, an 8,315-square-foot Georgian design drew general support. The board asked for more work on garage and carport visibility, parking and the street wall.

The 2480 Summit Drive teardown shows that a smaller house does not guarantee an easy hearing. It is one of the smaller new homes on this year's agendas, and it received one of the year's most critical preliminary reviews. The Town's standards point the same way. They say unenclosed parking "need[s] to be treated with sensitivity" so that neither the street nor the neighbors look at parked cars.

Where the square footage goes

Because the board reviews how big a house looks, some of the rules about how floor area is counted matter as much as the cap. Under the standards, basement area with exterior walls less than 2 feet above natural grade counts at 33 percent. Once those walls are 2 feet or more above grade, the area counts at 100 percent. Rooms with ceilings above 12 feet count the first 300 square feet normally and every square foot beyond that at 150 percent. Height tops out at 32 feet, inside an envelope that rises 22 feet at the setback lines and slopes inward at 45 degrees.

The board's comments followed the same logic. At 2900 Ralston Avenue, an addition and renovation totaling 12,542 square feet, members praised the design for reducing bulk by placing area below grade. The project was approved.

There is also a procedural threshold at 8,000 square feet. For houses that size or larger, whether new or reached through an addition, the City Council makes the final design review decision. The Building and Planning Director may waive that step only if there is no unresolved public concern and the board approved the project with no dissenting votes. The 2555 Summit Drive house was approved at 7,996 square feet. 715 Brewer Drive was listed for formal review on Oct. 5 at about 8,535 square feet, which puts it above that threshold.

Why this matters in a $6 million market

In October 2026, MLSListings data showed a median single-family sale price in Hillsborough of $6,075,000 across 10 closed sales. Homes sold in a median of 9 days at 108 percent of list price, and the market held 1.5 months of inventory. The San Mateo County Association of Realtors' September 2026 report showed the same $6,075,000 median across 12 sales. In that month, sellers received 98 percent of list price on average and homes took an average of 42 days to sell. With only about a dozen sales a month, those swings reflect which homes happened to close more than any change in direction.

The homes that sold in September averaged 5,053 square feet on lots averaging 33,044 square feet. That works out to a floor area ratio of about 15 percent, against the 25 percent the formula allows on the first acre. On paper, a lot that size could hold roughly 8,260 square feet, more than 3,000 square feet above the average house that sold.

That unused allowance is what makes an older Hillsborough house tempting to price as a future rebuild. This year's record suggests valuing that potential with a discount. Approved houses came in well below the formula, two of the four in the table above needed a third meeting, and the board's concerns were massing, privacy and style rather than total square footage. In a market where homes sold in a median of 9 days in October, a buyer may have to settle on a price before an architect has drawn anything.

Before you write an offer on a house you plan to rebuild

1. Use 2026 approvals as your benchmark. Price the future house at a size the board has recently approved on comparable lots, not at the formula maximum.
2. Look at the neighbors' side yards. Privacy and screening drove the longest delays this year, and the board has made planting a condition of approval.
3. Ask your architect how the basement would be counted. Under the standards, wall height above natural grade decides whether below-grade space counts at 33 percent or in full.
4. Ask the Planning Division where a planned house falls relative to 8,000 square feet. That size triggers City Council review unless the waiver conditions are met.
5. Plan for several months of meetings. This year's approvals took two or three meetings, and an approval lapses if no building permit is issued within a year.

Everything above describes the Town's published standards and its public meeting record. It is general information and not legal or financial advice. Confirm what applies to a specific property with the Town's Planning Division and your own architect or attorney.

If you are weighing an older Hillsborough home on what it could become, or getting ready to sell one, Ryan LeDoux and the LeDoux Group can compare your lot with this year's design review record and help you set a price. Request your free home valuation.