San Mateo County Luxury Homes for Sale

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

San Mateo County’s estate homes are concentrated in four large-lot towns, Atherton, Hillsborough, Woodside and Portola Valley, with more on the hillsides of the bayside cities and along the Coastside around Half Moon Bay. What matters most is that each estate town runs its own design review: Hillsborough’s board hears every new house and teardown, Woodside’s board advises on every residential application, and Atherton caps floor area as a share of the lot. If the home is in the City of San Mateo, a city conveyance tax of 0.5% (1.5% at $10 million or more) applies on top of the county tax.

This page covers where estates are and what to check. It gives no prices or market statistics; ask us for a current comparable-sales review.

At a glance

Item	What applies in San Mateo County
Who sets the rules	Each of the county’s 20 cities and towns inside its limits; the county in unincorporated areas such as Emerald Hills and the Midcoast
Estate-town design review	Hillsborough Architecture and Design Review Board; Woodside Architectural and Site Review Board; Portola Valley Architectural and Site Control Commission
Atherton floor area (R-1A)	18% of lot size on lots of one acre or more (Code 17.32.040)
Transfer tax	County $1.10 per $1,000; City of San Mateo adds 0.5% below $10 million and 1.5% at $10 million or more (Clerk-Recorder)
FAIR Plan residential limit	$3 million per location; water, liability and theft need a separate policy (CDI)
2026 one-unit conforming loan limit	$1,249,125; larger loans are jumbo (FHFA county list)

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Where to look in San Mateo County

Atherton. Atherton real estate consists largely of single-family homes on large lots, governed by the town’s R-1A standards, and Atherton does not appear on Caltrain’s current station list. Estate infrastructure, from long driveways to older pool and drainage systems, is covered in our guide to existing estate infrastructure in Atherton.

Hillsborough. Hillsborough real estate is a town of large-lot single-family estates on hillside and flat sites, on water from a BAWSCA member. See our Hillsborough estate site inspections guide.

Woodside and Portola Valley. Woodside real estate and Portola Valley real estate offer large-lot and acreage homes, some with equestrian facilities; our page on Woodside residential and equestrian property covers what differs. Confirm the water provider and any well or septic system by parcel.

Bayside cities and hills. Menlo Park real estate, Burlingame, San Mateo real estate and unincorporated Emerald Hills real estate above Redwood City include larger homes on city lots and hillside parcels, closer to Caltrain and US 101.

The Coastside. Half Moon Bay real estate, El Granada real estate, Montara real estate and Moss Beach include coastal homes and rural parcels in the Coastal Zone, served by Coastside County Water District or the Montara Water and Sanitary District. For vacant or rural coastal parcels, see Coastside land.

Several unincorporated areas carry a city mailing address. Confirm jurisdiction by parcel; our unincorporated San Mateo County page explains the check.

What to check before you buy

Town design review

If you plan to rebuild, add on or landscape, the town’s review process sets your timeline. Here is what the codes and town pages say:

Town	Review body	What it reviews
Hillsborough	Architecture and Design Review Board, five members (Chapter 2.12)	New dwellings; additions over 500 sq ft or visible second-story additions; teardowns (50% or more of exterior walls removed); accessory structures of 500 sq ft or more; tennis courts; landscaping for new homes and teardowns
Woodside	Architectural and Site Review Board, five members (town page)	Residential projects for neighborhood character, site layout, building design and landscaping; recommends to the Planning Director or Planning Commission
Atherton	Town planner checks R-1A standards (Code 17.32.040)	Setbacks, height, floor area and accessory structure limits

In Hillsborough, smaller exterior changes go to staff review, swimming pools and repainting are exempt, and board decisions can be appealed to the city council within 15 days, per the code. Woodside’s board advises rather than decides, and can suggest changes or conditions.

Atherton’s R-1A standards are specific. Front and rear yards for the main building are 60 feet minimum on standard lots; main buildings are limited to 30 feet in height, or 34 feet with a special structure permit; floor area is 18% of lot size on lots of an acre or more, with no more than 7.5% of lot size above the first floor; and accessory structures are limited to 1,200 square feet per acre of lot area, not counting pools, tennis courts and garages. Before you buy a home with expansion in mind, run the floor-area math on the actual lot.

Our estate town design review guide compares the four towns in more depth, including Portola Valley’s commission.

Coastal Zone homes

On the Coastside, development generally needs a coastal development permit. The California Coastal Commission explains that once it certifies a Local Coastal Program, the city or county issues most of these permits, while the Commission keeps appeal authority over certain projects. In the unincorporated Coastal Zone, short-term rentals need a county permit and are limited to 180 rented nights a year, not counting nights the owner is present, under Zoning Code Chapter 8.368 (third-party reproduction; confirm with county planning).

Fire hazard zones and insurance

The State Fire Marshal’s fire hazard severity zone maps classify land as Moderate, High or Very High. State Responsibility Area maps took effect April 1, 2024, and Local Responsibility Area maps, which cover incorporated towns, were released in phases from February 10 to March 24, 2025. Wooded hillside estates are worth checking on the map viewer.

In a High or Very High zone, Civil Code 1102.19 requires the seller to provide documentation of compliance with defensible space rules, or a written agreement under which the buyer obtains it. See our AB 38 defensible space inspection guide.

Get insurance quotes during your contingency period. The California FAIR Plan covers residential property up to $3 million per location as a limited fire policy, per the Department of Insurance, so water, liability and theft need a separate difference-in-conditions policy. For a large estate, compare that limit with the rebuild estimate. See our FAIR Plan guide for homebuyers.

Sewer laterals and utilities

Some Peninsula cities and sanitary districts have sewer lateral rules that can apply at sale; read our sewer lateral requirements at sale before you negotiate repair credits. On rural Woodside, Portola Valley and south coast parcels, ask for well and septic permit records and confirm requirements with San Mateo County Environmental Health.

Owning and financing an estate home

Transfer tax. The county documentary transfer tax is $1.10 per $1,000, per the Clerk-Recorder. The City of San Mateo adds a conveyance tax under Municipal Code 3.48.010: 0.5% of value below $10 million and 1.5% at $10 million or more, effective December 22, 2022. Confirm whether any other city levies one with your title officer. See California transfer tax.

Jumbo financing. San Mateo County’s 2026 one-unit conforming loan limit is $1,249,125, per FHFA, the national ceiling. Above that, a loan is jumbo and follows the lender’s own rules. Limits reset each year. See our jumbo loans guide.

Private and off-market sales. Many estate owners prefer discretion. We handle private and off-market sales and can explain what that approach trades away in exposure.

Questions people ask

Does Hillsborough require design review for a new house?

Yes. New dwellings, teardowns, additions over 500 square feet and visible second-story additions go to the five-member Architecture and Design Review Board.

What counts as a teardown in Hillsborough?

A renovation that removes 50% or more of the exterior walls, under Chapter 2.12. It is reviewed like a new dwelling.

How much house can I build on an Atherton lot?

In R-1A, floor area is 18% of lot size on lots of one acre or more, with no more than 7.5% of lot size above the first floor.

What is the height limit in Atherton?

30 feet for main buildings, or 34 feet with a special structure permit, under Code 17.32.040.

Does Woodside’s review board approve projects?

It recommends. The Architectural and Site Review Board advises the Planning Director or Planning Commission and can suggest changes or conditions.

What transfer tax applies in the City of San Mateo?

0.5% of value below $10 million and 1.5% at $10 million or more, on top of the county’s $1.10 per $1,000.

Can I rent a Coastside home short term?

In the unincorporated Coastal Zone, only with a county permit and no more than 180 rented nights a year.

Where does a jumbo loan start in San Mateo County?

Above $1,249,125 for a one-unit home in 2026, per FHFA.

Sources & notes

Notes: Hillsborough’s code was read from a third-party reproduction; confirm with the town. Portola Valley’s commission and any Hillsborough City Council size threshold were not verified for this page. Atherton side-yard rules (Table 17.38.010) and minimum lot sizes were not reviewed. Transfer taxes in cities other than San Mateo, and water, well and septic arrangements in Woodside, Portola Valley and the south coast, must be confirmed by parcel. Rules change; verify before you buy.

General information, not legal, tax or lending advice. Updated November 2026. Primary sources are linked in this guide.

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