Multifamily and Duplex Properties for Sale in Portola Valley: Zoning and Rent Rules

What multifamily in Portola Valley looks like

Portola Valley has very little traditional multifamily housing. Its rental market is mostly single-family homes, homes with ADUs, and a small amount of institutional or affiliated housing. That began to change in 2024 and 2025, when the town created multifamily and mixed-use districts for its 2023–2031 Housing Element sites. An investor here is usually buying a house with an ADU, a rare duplex, or land in one of the new districts. For two to four units, see financing 2-4 unit properties; for larger projects, apartment building loans.

Where the zoning allows it

Section 18.06.010 lists the town’s districts. These allow two or more homes on a parcel:

By-right affordable housing. Under Section 18.15.025, a housing development in R-MF of at least 20 units an acre, with 20% or more of its units affordable to lower-income households, is permitted without discretionary action. The ASCC still checks it against objective standards. The R-MF chapter was most recently amended by Ordinance 2025-452, adopted April 23, 2025.

Named sites. The R-MF chapter calls out two sites:

• Glen Oaks. Density and floor-area ratios are calculated on an estimated four developable acres.
• Dorothy Ford Park. A 2.48-acre portion of the park site, excluding the little league field and its parking lot, may be developed as high-density housing. There, owner-occupied or rental multifamily is allowed by right when at least 20% of units are affordable to lower-income households.

Design rules. At least 15% of units in an R-MF project must meet universal design standards. Affordable units must use the same exterior materials and details as market-rate units. The chapter’s purpose statement also calls for fire-resilient design.

ADUs and SB 9. ADUs and JADUs follow Chapter 18.25, which we did not review in detail; state ADU law sets the minimum. SB 9 applies to qualifying single-family lots, though geologic and fire hazard limits can rule out a split. See our ADU investment guide and SB 9 lot split guide.

Rent rules: state law only

The Attorney General’s rent cap page, updated July 16, 2026, places San Mateo County in the San Francisco area, with increases on covered units capped at 8.8% from August 1, 2026 through July 31, 2027. Portola Valley is not on the AG’s list of cities with local rent ordinances. Many rentals here are single-family homes, which may be exempt from AB 1482’s cap when the owner is not a corporation and gives the required notice. See our AB 1482 guide and just cause eviction guide.

Portola Valley rental property rules

Regulatory agreements. Projects using the by-right path or the Dorothy Ford Park provisions carry lower-income unit requirements, so expect recorded affordability terms that limit rents on those units. Ask for every regulatory agreement before buying.

Transfer tax. The County’s documentary transfer tax is 55 cents per $500; the County names only the City of San Mateo as adding a city tax, and we found no town tax. Confirm with escrow.

Short-term rentals. We did not verify Portola Valley’s short-term rental rules; confirm with the town before planning short stays.

Geologic hazards, fire and creeks

Geologic maps. The Town Council approved a Geologic Map and a Ground Movement Potential Map on November 8, 2017, and adopted them as policy for town decisions. Land use policies for each mapped area are in Resolution 2746-2017. A buyer planning an ADU, a second unit or any addition should locate the parcel on both maps first and budget for geotechnical work.

Fire. The R-MF chapter builds fire-resilient design into its purpose. Expect defensible-space and building-hardening requirements on hillside parcels, and confirm insurance availability early.

Slopes and creeks. The S-D slope density combining district can lower allowable density on steep land. The town’s Floodplain combining district (18.32) and creek setback chapter (18.59) apply near creeks.

Older homes. Older wood-frame homes and cottages warrant a seismic retrofit review. Any building of three or more units with elevated decks needs SB 721 balcony inspections.

Underwriting a Portola Valley multifamily purchase

1. Confirm the district and density range, and whether the parcel is in the town or unincorporated County.
2. Locate the parcel on the 2017 geologic and ground movement maps.
3. Classify units under AB 1482 and model covered increases at or below 8.8%, and apply any regulatory agreement rents to affordable units.
4. Confirm ADU permits and any recorded covenants.
5. Collect leases and estoppel certificates.
6. Rebuild expenses with reassessed taxes, wildfire insurance and geotechnical monitoring in our rental property analysis.

Questions people ask

Sources & notes

1. Portola Valley Chapter 18.06, Districts (GoCodebook)
2. Portola Valley Chapter 18.15, R-MF
3. Portola Valley Chapter 18.23, MU
4. Town of Portola Valley, Geologic and Ground Movement Potential Maps
5. California Attorney General, rent caps
6. San Mateo County ACRE, documentary transfer tax

Note: We did not review the AH or ADU chapters, short-term rental rules, the map PDFs or Resolution 2746-2017 itself, or the status of any Housing Element site project.

General information, not legal or tax advice. Last reviewed October 2026 by Matthew Martinez.

Related: Portola Valley real estate guide · Commercial real estate in Portola Valley · Multifamily investing guide · Investor services