Multifamily and Duplex Properties for Sale in Emerald Hills: Zoning and Rent Rules

What multifamily in Emerald Hills looks like

Emerald Hills is a hillside neighborhood of single-family homes, so income property here rarely means an apartment building. It means a house with a permitted second dwelling unit or guest house, a home with a newer ADU or JADU, or a lot large enough to consider an SB 9 split. The returns come from adding or legalizing units within tight hillside limits, which makes permit history the first thing to check. For financing small income properties, see financing 2-4 unit properties; for larger buildings in nearby Redwood City, see apartment building loans.

Where the zoning allows it

Emerald Hills is unincorporated, so the County’s Title 8 code applies. The district that carries the Emerald Lake Hills rules is RH Residential Hillside.

Floor area is the binding limit. Because the cap counts every building on the site, an ADU or guest house uses up the same floor area allowance as the main house unless state ADU law overrides it. On a 10,000-square-foot lot, the RH limit is 3,000 square feet for everything. Check whether state ADU rules let a unit exceed the local limit on that lot.

ADUs. The County’s ADU page puts inland ADU rules in Chapter 8.392. It sets four-foot side and rear setbacks and imposes no owner occupancy for ADUs, though a JADU without its own sanitation needs a recorded owner-occupancy restriction. See our ADU investment guide.

SB 9. State lot split and two-unit rules may apply to qualifying single-family parcels, subject to hillside, fire and access exclusions. See our SB 9 lot split guide.

Rent rules: state law only

There is no local rent ordinance in Emerald Hills. The Attorney General’s rent cap page, updated July 16, 2026, places San Mateo County in the San Francisco Area. Covered units may rise up to 6.3% for increases from August 1, 2025 and 8.8% from August 1, 2026 through July 31, 2027. Many Emerald Hills rentals are single-family homes owned by individuals, which can be exempt from the cap and just-cause rules if the lease contains the required notice. A home plus an ADU, where the owner lives in one unit, can also be exempt. Verify each case. See our AB 1482 guide and just cause eviction guide.

Emerald Hills rental property rules

• The 55-permit limit. RH limits new residential building permits in Emerald Lake Hills to 55 per calendar year, under a rule dating to Ordinance 3194 of October 31, 1989. Disaster rebuilds, remodels under 50% of replacement value and deed-restricted affordable housing are excepted. The code text does not say how ADUs are counted, so ask County Planning before relying on a new unit.
• Design review. Emerald Lake Hills has a County Design Review Officer. Under an ordinance the Board adopted in June 2026, design review outside the Coastal Zone became staff-level and ministerial on July 23, 2026, which should make review of new units more predictable.
• Short-term rentals. Unincorporated hosts register for transient occupancy tax through HdL. Check County short-term rental rules, and whether ADU rules prohibit short stays, before relying on that income.
• Transfer tax. The County’s documentary transfer tax is $1.10 per $1,000, with no city tax.

Sewer, slopes and fire access

The Emerald Lake Heights Sewer Maintenance District, formed in 1947 and governed by the Board of Supervisors through Public Works, provides sewer maintenance and replaces deteriorating lines in unincorporated Emerald Lake Hills. Confirm whether a parcel is connected or on septic, and what connection or capacity fees apply to a second unit.

Slopes drive construction cost. RH caps grading at 1,000 cubic yards per site and measures height from natural grade. One side yard must allow fire access to the rear of the lot. Narrow, winding roads can also affect fire department access requirements for new units. Older homes with converted lower floors or garage units warrant a permit search and a seismic retrofit review; buildings with three or more units and elevated decks need SB 721 balcony inspections.

Underwriting an Emerald Hills income property

1. Pull County permits for every unit; count only legal second units and ADUs.
2. Measure total floor area and coverage against the RH limits before planning additions.
3. Ask Planning how the 55-permit cap would treat a planned unit.
4. Classify each unit under AB 1482, including any single-family exemption notice, and model covered increases at or below 8.8%.
5. Collect leases and estoppel certificates.
6. Rebuild expenses with reassessed taxes, sewer district charges, wildfire insurance and slope maintenance in our rental property analysis.

Questions people ask

Sources & notes

1. Title 8, Chapter 8.110 RH Residential Hillside (GoCodebook)
2. San Mateo County Planning, zoning regulations
3. San Mateo County Planning, ADUs
4. San Mateo County Planning, Emerald Lake Hills Design Review Officer
5. San Mateo County LAFCo, Emerald Lake Heights Sewer Maintenance District
6. San Mateo County, transient occupancy tax
7. San Mateo County Assessor-County Clerk-Recorder, documentary transfer tax
8. California Attorney General, rent caps

Note: We did not review the zoning map, so some Emerald Hills parcels may be in other County districts. ADU points come from the County ADU page as summarized on our San Mateo County guide. We did not review fire hazard maps or the County short-term rental rules.

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

Related: Emerald Hills real estate guide · Commercial real estate in Emerald Hills · Multifamily investing guide · Investor services