Belmont Neighborhoods by Their Lots: Lot Sizes, Flood Zones and Fire Zones

San Mateo County’s public parcel layer gives an outline and a property use code for every parcel. We took the 6,685 parcels with the county’s single-family use code, 1,500 square feet or more, inside our nine Belmont neighborhood guides, measured each lot from its outline, checked its center against FEMA’s flood map and checked each lot against CAL FIRE’s fire hazard severity zone maps. The layer has no year built, house size or city-limit line, so this post covers our nine guides rather than the city as a whole. Parcel outlines downloaded October 2026; the county’s use codes were last updated in June 2020. There are no addresses or owner details here.

The short answer

• Across our nine Belmont guides, the median single-family lot is 6,570 sq ft.
• Largest and smallest lots (guides with at least 150 single-family lots): largest in Belmont Heights (8,960 sq ft), McDougal (8,530 sq ft) and Cipriani (6,750 sq ft); smallest in Western Hills & Carlmont (3,900 sq ft), Sterling Downs & Homeview (5,080 sq ft) and Downtown Belmont (6,300 sq ft).
• Flood zones: 104 of the 6,685 lots (2%) have their parcel center in a FEMA high-risk flood zone (95 in AE and 9 in A); the most are in Island Park (95) and McDougal (7).
• Fire zones: 1,612 lots (24%) are at least partly in a CAL FIRE fire hazard severity zone: all Moderate; none are High or Very High. The most are in Belmont Heights (637) and Plateau-Skymont (492).

Neighborhood by neighborhood

Largest median lot first. “Single-family lots” counts parcels with the county’s single-family use code whose center falls inside each guide’s outline; no lot falls in two guides. Each name opens its guide. Island Park and Western Hills & Carlmont have small medians because many of their detached houses sit on small planned-development lots.

What stands out

• Belmont Heights has the biggest lots: a median of 8,960 sq ft, about 1.4 times the median across our guides.
• Fire zones concentrate in Belmont Heights: 637 of its 749 lots (85%) touch one.
• Flood-zone lots concentrate in Island Park: 95 of its 102 lots (93%), in zone AE.

Flood zones, neighborhood by neighborhood

Single-family lots in FEMA high-risk zones inside each guide’s outline, the share of the guide’s lots they make up, and the zones; most first. The other six guides have none.

What the flood zones mean

• Zone A: a 1%-a-year chance of flooding, where FEMA hasn’t set a base flood elevation.
• Zone AE: the same 1%-a-year risk, with a base flood elevation set.
• Zone X: moderate to minimal risk, outside the 1%-a-year floodplain.
• Insurance: if the house itself is in an A or V zone, lenders on federally backed mortgages require flood insurance; a flood zone determination for the address settles it. In zone X it’s optional.

Fire hazard zones, neighborhood by neighborhood

CAL FIRE maps how severe the wildfire hazard is across California, in three classes: Moderate, High and Very High. Single-family lots inside each guide’s outline, by the highest zone that touches any part of the lot; most severe first. No lot touches a Very High zone. The other five guides have none in any zone.

What the fire zones mean

• Hazard, not risk. CAL FIRE’s Office of the State Fire Marshal says the maps describe hazard: the physical conditions, like vegetation, terrain, fire history, embers and typical fire weather, over 30 to 50 years. They don’t count home hardening, defensible space or fuel reduction, which change the risk to a particular home (OSFM).
• Two kinds of map. Inside city limits (Local Responsibility Areas) we used CAL FIRE’s 2025 map; where the state is responsible for wildfire protection (State Responsibility Areas), its State Responsibility Area map. Land outside the three classes is shown as non-wildland or unzoned (OSFM).
• What a zone can bring. Depending on the zone and the kind of area, stricter building standards for new construction and additions, defensible-space rules, and a line on the seller’s natural hazard disclosure. Belmont’s building department can say which apply to a specific address.

Reading it right

• A use code isn’t a zoning district. We counted parcels the county codes as single-family residences, 1,500 square feet or more; the codes date from June 2020, so a few newer houses may be missing or coded otherwise, and townhomes and condos aren’t counted.
• Lot sizes are measured from the county’s parcel outlines, so they can differ from a survey by a few percent.
• We checked the center of each lot against FEMA’s National Flood Hazard Layer. A lot can straddle two zones, and maps change, so check the current FEMA map for the exact address.
• The flood zone covers the land, not the house. A house can sit above the base flood elevation even in a high-risk zone. An elevation certificate settles it and can lower the insurance price.
• The fire zone describes the land around a house, not how the house is built or how the lot is kept. CAL FIRE’s zone viewer shows any parcel, and a seller’s natural hazard disclosure report states the zones for that property.
• A median isn’t a verdict. It describes the lots, not which neighborhood is right for you.

Go deeper

Belmont Housing Market by the Numbers covers prices and bidding, The Most Expensive Streets in San Carlos & Belmont goes street by street, and San Carlos vs. Belmont compares the two cities. Flood & Fire Zones by Neighborhood compares every guide we write, and the Belmont city guide links every neighborhood guide.

Buying, selling or rebuilding in a flood or fire zone?

A Property Nerd can pull the zoning, the lot, the flood and fire zones, any elevation certificate and the recent sales on your street before you write an offer, set a price or plan a rebuild. Call (408) 373-1660 or (650) 383-8606, or book a strategy call. Commissions are negotiable, and we offer bundled services, so ask us what’s included.