42 Topside Way
Mill Valley 94941 · Strawberry · Unincorporated Marin · Coordinates: 37.88090, -122.50106
Executive Verdict · Public-Records Synthesis
Zoned RSP-5 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and zero mapped flood, fire, or fault hazard overlaps; benchmark value $2,316,000 ($2,038,000–$2,594,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned RSP-5 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 15,420 sq ft lot.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$28,050 contributory est.)
Public building records show issued construction/renovation work on this parcel (9 total permits, latest Dec 17, 2025).
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)
- ! Delayed or open permit activity on this parcel
Plumbing / water heater / sewer (168685): Issued after 2 mo — slower than 90% of plumbing / water heater / sewer permits in Unincorporated Marin (median 0d, 90th pct 0d, n=2,211).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (review-time benchmark)
- ! 4 slow or stalled nearby projects within ½ mile
Closest lead: New home (410 ft N, entitled). 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 (~$27,084/yr at $2,316,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,257/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:
- 15,420 sq ft (0.35 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 42 TOPSIDE WAY
Zoning & Land Use
RSP-5 — Residential Single Family Planned (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned RSP-5 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned RSP-5, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned RSP-5, a single-family residential zone. The lot is 15,420 sq ft by the assessor, room for two lots of at least 1,200 sq ft, each at least 40% of the original.
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: $2,038,000 – $2,594,000 · 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
- Plumbing / water heater / sewer (168685) (Issued)On this parcel
Issued after 2 mo — slower than 90% of plumbing / water heater / sewer permits in Unincorporated Marin (median 0d, 90th pct 0d, n=2,211).
- New garage / accessory structure (83941) (Applied)On this parcel
Pending in review for 7.3 yr (16.3× the 164d median) — slower than 90% of new garage / accessory structure permits in Unincorporated Marin (median 164d, 90th pct 485d, n=356).
- New home (Entitled)410 ft N
In "Entitled" for 5.1 yr (since Sep 30, 2021), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- Demolition at 171 Great Cir Dr (Applied)0.1 mi N
In "Applied" for 15 mo (since Aug 14, 2025), exceeding the 55d median and 261d 90th percentile for demolition permits in Unincorporated Marin (n=130).
Entity-resolved builders & contractors in ½ mile: Dan Young Construction (1 on parcel, 1 in ½ mi · Remodel / interior alteration); Home Team Services Remodeling (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer); Bellows Plumbing Heating And Air (1 on parcel, 1 in ½ mi · HVAC / heat pump); Golden Gate Home Improvement (1 on parcel, 1 in ½ mi · Windows / doors / siding); King Electric (1 on parcel, 1 in ½ mi · Electrical / panel).
Permit & Project History on This Parcel (9 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B45210 | Plumbing / water heater / sewer | Issued | Iss. Dec 17, 2025 | $19,800 | Minor bathroom improvements consisting of like-for-like replacement of existing finishes and fixtures. Work includes rem… |
| 168685 | Plumbing / water heater / sewer | Issued | Iss. Jul 1, 2021 | $300,000 | Repl & Expand 2-Level Decks; Fire Pit, Heaters |
| B25680 | Electrical / panel | Issued | Iss. May 7, 2021 | $7,160 | Upgrade electric meter panel to 400-amp/ 320-amp actual — Service Upgrade |
| 166384 | Plumbing / water heater / sewer | Issued | Iss. Nov 25, 2020 | $10,500 | Generator |
| B22491 | HVAC / heat pump | Issued |