229 Rosemont Ave
Mill Valley 94941 · Almonte · Unincorporated Marin · Coordinates: 37.88440, -122.52734
Executive Verdict · Public-Records Synthesis
Zoned R1-B1 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and zero mapped flood, fire, or fault hazard overlaps; benchmark value $2,134,000 ($1,878,000–$2,390,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned R1-B1 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 7,884 sq ft lot. Local precedent is active with 7 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$8,677 contributory est.)
Public building records show issued construction/renovation work on this parcel (6 total permits, latest Nov 14, 2025).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
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)
- ! 6 slow or stalled nearby projects within ½ mile
Closest lead: New home at 217 Cleveland Ave (360 ft NW, issued). 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 (~$24,991/yr at $2,134,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,083/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:
- 7,884 sq ft (0.18 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 229 ROSEMONT AVE
Zoning & Land Use
R1-B1 — Residential Single Family (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned R1-B1 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned R1-B1, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned R1-B1, a single-family residential zone. The lot is 7,884 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: $1,878,000 – $2,390,000 · 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
- New home at 217 Cleveland Ave (Issued)360 ft NW
Active in "Issued" for 9.7 yr (first record Feb 21, 2017) with no new permit activity recorded in 2.3 yr. High-impact scale (1 housing unit, $875,000 declared valuation across 1 permit).
- Accessory dwelling unit at 131 Yale Ave A (Issued)0.26 mi N
Active in "Issued" for 4.8 yr (first record Jan 19, 2022) with no new permit activity recorded in 3.4 yr. High-impact scale (1 housing unit, $1,000,000 declared valuation across 1 permit).
- New home at 125 Morning Sun Ave (Issued)0.34 mi N
Active in "Issued" for 8.1 yr (first record Oct 15, 2018) with no new permit activity recorded in 7.8 yr. High-impact scale (1 housing unit, $900,000 declared valuation across 3 permits).
- New commercial building at 100 Harvard Ave (Issued)0.41 mi NW
Active in "Issued" for 23 mo (first record Dec 26, 2024) with no new permit activity recorded in 18 mo. High-impact scale ($6,500,000 declared valuation across 1 permit).
Entity-resolved builders & contractors in ½ mile: Ernest Ongaro And Sons (3 on parcel, 3 in ½ mi · Electrical / panel); Tesla Energy (1 on parcel, 1 in ½ mi · Solar / battery storage); Window And Door Factory Of California (1 on parcel, 1 in ½ mi · Windows / doors / siding); Arrow Deck And Construction (1 on parcel, 1 in ½ mi · Other); Owner Builder (86 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (6 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B44786 | Plumbing / water heater / sewer | Issued | Iss. Nov 14, 2025 | $3,574 | Remove(E)NG WH in the crawl space and Install(N) NG WH in the same location. — Replace Plumbing Fixtures(s) |
| B44011 | Electrical / panel | Issued | Iss. Sep 23, 2025 | $6,003 | Remove (E) 100A main panel located in garage, install (N) 200A main outside of garage in same location. Remove 2 (E) sub… |
| B43934 | HVAC / heat pump | Issued | Iss. Sep 17, 2025 | $21,488 | Replace furnace with air handler, install heat pump NEW in backyard. Replace 11 runs of ducting located in crawl space —… |
| B35650 | Windows / doors / siding | Issued | Iss. Oct 4, 2023 | $15,000 | Replace 9 windows like for like — Non-structural Door/Window Replacement |
| 169358 |