21 De Silva Island Dr
Mill Valley 94941 · Strawberry · Unincorporated Marin · Coordinates: 37.88776, -122.51487
Executive Verdict · Public-Records Synthesis
Zoned RMP-1.5-BFC in Unincorporated Marin with likely ministerial ADU eligibility and zero mapped flood, fire, or fault hazard overlaps; benchmark value $2,127,000 ($1,872,000–$2,382,000).
Upsides & Opportunities
- ✓ Ministerial ADU / JADU pathway likely eligible
Zone RMP-1.5-BFC allows residential use qualifying for ministerial ADU review under state law.
Source: Unincorporated Marin zoning · CA Gov. Code 66314
- ✓ 1 documented municipal building permit on file
On-parcel permit history is indexed through Mar 23, 2023, letting you verify roof, HVAC, electrical, or structural work against seller disclosures.
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
- ✓ Above-average reinvestment in Strawberry
43 substantial renovation & housing permits over 24 months (28.4 per 1,000 parcels vs. 16.4 citywide baseline) (#1 of 22 neighborhoods).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (Strawberry)
Watchouts & Due Diligence
- ! Mapped flood awareness zone (Zone X: minimal flood hazard)
all of the lot of the parcel intersects Zone X: minimal flood hazard. Outside mandatory federal SFHA insurance rules, but check local drainage and finished-floor requirements.
Source: FEMA National Flood Hazard Layer (parcel polygon)
- ! 5 slow or stalled nearby projects within ½ mile
Closest lead: Accessory dwelling unit at 25 Vista Del Sol (0.36 mi N, applied). Inspect timeline history before assuming near-term completion.
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) · HCD APR (½-mile radius)
- ! Year 1 Prop 13 tax reset (~$24,911/yr at $2,127,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,076/mo). Confirm exact Mello-Roos / CFD special assessments on the county tax bill.
Source: CA Const. Art. XIIIA (Prop 13) · County Tax Collector
Parcel & Assessor
- Lot size:
- 1,002 sq ft (0.02 ac)
- Assessor use:
- Single Family Attached
- Addresses on lot:
- 21 DE SILVA ISLAND DR
Zoning & Land Use
RMP-1.5-BFC — Residential Multiple Planned (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned RMP-1.5-BFC (multifamily residential): state law allows ADUs where homes are allowed. On a multifamily lot the state allowance is different: ADUs in non-living space of the building, plus up to eight detached ADUs.
- SB 9: two homes on the lotUnlikely
Zoned RMP-1.5-BFC (multifamily residential), not a single-family residential zone.
- SB 9: split into two lotsUnlikely
Zoned RMP-1.5-BFC (multifamily residential), not a single-family residential zone.
Mapped Hazard Zones on This Lot
- CAL FIRE Fire Hazard Severity Zone
- Not in a State-mapped fire hazard severity zone
- FEMA National Flood Hazard Layer
- Zone X: minimal flood hazard (all of the lot) · FIRM panel 06041C0469F, effective March 16, 2016
- CGS Alquist-Priolo Earthquake Fault Zone
- Not in an Alquist-Priolo Earthquake Fault Zone
Surrounding Rent & Value Benchmarks (Public Records)
Range: $1,872,000 – $2,382,000 · Status: Off market
HUD Small Area FMR (ZIP 94941) · FY 2026
Studio $2,730 · 1BR $3,270 · 2BR $3,960 · 3BR $5,060 · 4BR $5,240
Developments Deserving Closer Investigation & Active Area Builders
- Accessory dwelling unit at 25 Vista Del Sol (Applied)0.36 mi N
In "Applied" for 2.1 yr (since Oct 11, 2024), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- Accessory dwelling unit at 315 Richardson Dr (Applied)0.46 mi NE
In "Applied" for 2 yr (since Oct 31, 2024), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- New commercial building at 574 Redwood Hwy Frontage Rd Formerly (Issued)0.33 mi N
Active in "Issued" for 11.4 yr (first record Jun 15, 2015) with no new permit activity recorded in 11.1 yr.
- New home at 315 Richardson Dr (Issued)0.46 mi NE
Active in "Issued" for 12.1 yr (first record Oct 2, 2014) with no new permit activity recorded in 11.1 yr.
Entity-resolved builders & contractors in ½ mile: Romans Plumbing (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer); Owner Builder (8 in ½ mi · Remodel / interior alteration); Owner (6 in ½ mi · Remodel / interior alteration); Wci Gc (3 in ½ mi · Commercial tenant improvement); Flint Construction (3 in ½ mi · New garage / accessory structure).
Permit & Project History on This Parcel (1 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B33121 | Plumbing / water heater / sewer | Issued | Iss. Mar 23, 2023 | $4,175 | WATER HEATER REPLACEMENT IN EXISTING LOCATION (INTERIOR CLOSET) — Replace Plumbing Fixtures(s) |