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Atherton, Woodside, Portola Valley and Hillsborough Building Rules

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

Atherton’s building rules cap a house on a lot of an acre or more at 18% of the lot area, hold the main building to 30 feet unless the owner accepts larger setbacks or wins a special structures permit from the Planning Commission, and protect native oaks of 48 inches in circumference anywhere on the lot. Hillsborough, Woodside and Portola Valley each add a named design review body, which Atherton’s R-1A standards section does not: Hillsborough’s Architecture and Design Review Board, Woodside’s Architectural and Site Review Board, and Portola Valley’s Architectural and Site Control Commission.

For an estate buyer planning a remodel or rebuild, these rules decide how much house a lot can carry, and so part of what the land is worth. This page compares the four towns’ published floor-area, height and review rules as of October 2026, explains what to check before you write an offer on a teardown, and notes what each town does not publish, such as review timelines. Code text changes, so confirm every figure with the town’s planning staff for your parcel.

The four towns side by side

Town	Review body	House size rule	Height
Atherton	Town planner checks compliance; Planning Commission decides special structures permits	18% of lot area on lots of one acre or more; smaller lots (lot × 0.163) + 726 sq ft, minimum 2,250; upper floors no more than 7.5% of lot	30 ft standard; up to 34 ft with added setbacks or a special structures permit
Hillsborough	Architecture and Design Review Board holds a public hearing on new houses; a new house over 8,000 sq ft also needs City Council review	25% of net lot area for the first acre plus 15% of the net lot area over one acre	Envelope rising 22 ft above grade at the setback lines, then sloping inward at 45 degrees to a 32 ft maximum
Woodside	Architectural and Site Review Board, advisory to the Planning Director or Planning Commission	Main-residence caps by zone: 4,000 to 6,000 sq ft as a base outside R-1, up to 5,500 or 8,800 sq ft on larger parcels by exception (see below)	Check the zoning district
Portola Valley	Architectural and Site Control Commission	Adjusted maximum floor area from parcel size, average slope, geology or flood classification and zoning; main house plus required covered parking no more than 85% of it	Check the zoning district

Atherton figures are from the town’s municipal code (current through Ordinance 679, May 20, 2026). Hillsborough and Woodside figures are from the towns’ municipal code text as reproduced in GoCodebook’s code library (text as of October 4, 2026), a third-party copy, so confirm them against the official code. Portola Valley’s come from the town’s floor-area handout.

Atherton: generous lots, fixed formulas

Atherton’s R-1A standards in section 17.32.040 set floor area by formula. On a lot of one acre or more, total floor area is limited to 18% of the lot; a 1.5-acre lot (65,340 square feet) allows about 11,761 square feet. Floor area above the first floor of the main building may not exceed 7.5% of the lot, which pushes most of a large house onto one level.

The standard height limit is 30 feet, with sidewalls and columns at 22 feet. An owner can go to 34 feet, and 28-foot sidewalls, by adding five feet of setback for each foot of extra height, or by obtaining a special structures permit, which the Planning Commission decides on a town planner’s recommendation. Front and rear setbacks for main buildings are 60 feet on standard lots, and accessory structures are capped at 1,200 square feet per acre, not counting pools, tennis courts, garages and paving.

The code section we read describes the town planner reviewing applications for compliance and does not set up a separate architecture board for houses in R-1A. Our look at Atherton’s super-luxury market covers prices; this page covers what the rules let you build.

Hillsborough: design review for every new house

Hillsborough’s code, section 17.32.030, limits total covered floor area to 25% of net lot area for the first acre plus 15% of the net lot area beyond it, so a net acre allows about 10,890 square feet. A house must also have at least 2,500 square feet. Section 17.32.060 caps combined structural and hardscape coverage at 50% of net lot area, and at 40% of the street-line setback area, with a separate structural coverage table that scales with lot size.

Setbacks are a 25-foot strip along the street line and a 20-foot strip along other lot lines. For a house of 8,000 square feet or more, section 17.24.020 increases those setbacks by 15 feet in total, with at least five feet added on the street side. Height is set by an envelope in section 17.28.010: it starts at existing grade at the setback lines, rises 22 feet, then slopes inward at 45 degrees to a 32-foot maximum.

The Architecture and Design Review Board, five members under Chapter 2.12, holds a public hearing on new dwellings, teardown renovations, larger additions and tennis courts, among other projects, and can approve, conditionally approve or deny them. A new main house over 8,000 square feet is not approved until the City Council reviews it after a public hearing, under section 17.32.040. These figures come from the code text as a third party reproduces it, so have the town confirm them for your parcel.

Woodside: rural character and sliding caps

Woodside’s Architectural and Site Review Board has five members appointed by the Town Council, including a licensed architect and a licensed landscape architect when qualified candidates are available. It reviews residential applications for community character, site planning, building design and landscape, checks them against the town’s 2012 Residential Design Guidelines and General Plan, and makes recommendations to the Planning Director or Planning Commission. It meets on the first and third Mondays at 4:30 p.m.

Woodside’s zoning code, section 153.206, caps the main residence separately from total floor area. Outside R-1, the base cap is 4,000 square feet in SR and 6,000 square feet in RR and the SCP zones. On larger parcels an exception lets the cap rise on a sliding scale:

Zone	Base main-residence cap	Exception starts at	Exception cap	Full cap reached at about
R-1 (outside the Glens)	10% of lot area + 1,000 sq ft, up to 3,000 sq ft	0.458 acres	4,200 sq ft	0.69 acres
SR	4,000 sq ft	0.519 acres	5,500 sq ft	1.5 acres
RR	6,000 sq ft	1.439 acres	8,800 sq ft	4.5 acres
SCP-5	6,000 sq ft	1.450 acres	8,800 sq ft	7.5 acres
SCP-7.5	6,000 sq ft	2.669 acres	8,800 sq ft	11.25 acres
SCP-10	6,000 sq ft	3.680 acres	8,800 sq ft	15 acres

The last column is our arithmetic from the code’s formulas, not a figure the code prints. Below the starting size, SR, RR and SCP lots are held to the total floor area limits for nonconforming lots, and the code bars subdividing a lot below the acreage its exception relied on. The section also lists larger setbacks for big parcels that use the exception, and it was last amended by Ordinance 2025-647, effective May 8, 2025.

The exception is granted by the body and under the criteria named in sections 153.912 to 153.918, which we did not open. Ask planning staff which review your project would need.

Portola Valley: floor area adjusted for the land

Portola Valley does not use a single percentage. The town computes an adjusted lot size and an adjusted maximum floor area from four inputs: parcel area, average slope, geologic or flood-area classification, and zoning district, under zoning ordinance section 18.48.010. Steep or geologically constrained land therefore supports less house than the same acreage on gentle ground.

Within that maximum, the main residence plus required covered parking may use no more than 85%, leaving 15% for accessory structures, and every lot needs at least two covered spaces of at least 400 square feet. Impervious surface is counted separately and includes paving, pools, artificial turf, compacted gravel and wide gravel paths. The Architectural and Site Control Commission, five appointed commissioners meeting on the second and fourth Mondays, reviews specified structures, additions, clearing, excessive grading and the destruction of trees and shrubbery under Chapter 18.64.

Trees, geology and other site limits

Trees can shape a site plan as much as floor area. Atherton defines a heritage tree to include valley, coast live and blue oaks anywhere on a lot with a trunk circumference of at least 48 inches, or 15.2 inches in diameter, measured 54 inches above natural grade. Other trees of that size outside the main buildable area also qualify, and a protection zone around each can extend onto neighboring property.

Portola Valley’s commission reviews the destruction of trees and shrubbery as part of site control, and Woodside’s board reviews landscape elements. Ask each town for its tree rules and any arborist report requirement before you plan a footprint.

Geology and hazards also matter. Portola Valley writes geology directly into its floor-area formula, and parts of the Peninsula hills fall within state-mapped hazard zones; our page on earthquake fault zones in California explains how those maps work in a sale.

Before you write an offer on a teardown or remodel

Get the lot’s real numbers. Net lot area, slope and any easements change the floor-area result. A survey beats a listing’s acreage.
Run the formula with the town. Ask planning staff to confirm the allowed floor area, height and setbacks for the parcel, and whether existing structures count against them.
Find out which review applies. Board review, Planning Commission permits or a Council hearing add steps. None of the town pages we read publish a standard timeline, so ask staff for typical review times.
Order an arborist’s tree survey. Protected trees can fix where a house can go.
Check geology and utilities. Slope, landslide or fault mapping, sewer or septic, and water service can each limit or delay a project.
Write contingencies to match. Allow enough investigation time to get these answers, or price the uncertainty in.

Our guide to buying a teardown in the Bay Area covers financing and demolition questions, and the San Mateo County property workbook helps organize the parcel records.

Selling an estate lot or older house

If your property’s value rests partly on what a buyer could build, document it. Gather the survey, prior approvals, permit history and any arborist or geotechnical reports, and ask an architect for a written floor-area calculation under the current code.

Clear, documented numbers give buyers less to discount and reduce price arguments later. Our guide to selling a luxury home covers presentation and pricing, and buyers can start with buying a luxury home.

Questions people ask

How big a house can I build in Atherton?

On a lot of one acre or more, total floor area is limited to 18% of the lot. Smaller lots use (lot area × 0.163) + 726 square feet, with a 2,250-square-foot minimum, and upper floors are limited to 7.5% of the lot.

What is the height limit in Atherton?

The standard limit for main buildings is 30 feet. Up to 34 feet is possible with five feet of added setback per extra foot, or with a special structures permit from the Planning Commission.

What does Woodside’s ASRB do?

The Architectural and Site Review Board reviews residential and non-residential applications for community character, site planning, building design and landscape, and makes recommendations to the Planning Director or Planning Commission.

What is Portola Valley’s ASCC?

The Architectural and Site Control Commission is a five-member body that reviews specified structures, additions, clearing, excessive grading and the destruction of trees and shrubbery. It meets on the second and fourth Mondays of the month.

Does Hillsborough require design review?

Yes, for new houses and several other project types. The town code has the Architecture and Design Review Board hold a public hearing, and a new main house over 8,000 square feet also needs City Council review after a public hearing.

How big a main house can I build in Woodside?

The code caps the main residence at 4,000 square feet in SR and 6,000 in RR and SCP zones, rising by exception on larger parcels to 5,500 or 8,800 square feet. Total floor area limits still apply.

What counts as a heritage tree in Atherton?

Valley, coast live and blue oaks anywhere on a lot with a trunk circumference of at least 48 inches measured 54 inches above grade, plus other trees of that size outside the main buildable area.

How long does design review take in these towns?

None of the town pages we read publish a standard timeline. Ask planning staff for typical times for your project type and build them into your contract and schedule.

This is general information, not legal advice. Zoning and design rules are applied parcel by parcel, so confirm the numbers with the town’s planning department and have a California land use attorney or architect review any project the purchase depends on.

If you are weighing an estate purchase or sale in these towns, Diamond can help you gather the parcel facts before you commit; contact us or explore our luxury real estate services. For the wider county picture, see the San Mateo County guide, and for estates south of the county line, our Santa Clara County luxury homes page.

Sources & notes

Last reviewed October 2026 by Matthew Martinez.